Cold adaptation in Arctic and Antarctic fungi

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Review

Blackwell Science Ltd

Research review

Cold adaptation in Arctic and

Antarctic fungi

Clare H. Robinson

Division of Life Sciences, King’s College, University of London, Franklin-Wilkins Building, 150

Stamford Street, London SE1 9NN, UK

Author for correspondence:

Clare H. Robinson Tel: +44 (0)20 7848 4352 Fax: +44 (0)20 7848 4500 Email: [email protected]

Received:

27 October 2000

Accepted

:

15 February 2001

Summary

Growth and activity at low temperatures and possible physiological and ecologicalmechanisms underlying survival of fungi isolated from the cold Arctic and Antarcticare reviewed here. Physiological mechanisms conferring cold tolerance in fungi arecomplex; they include increases in intracellular trehalose and polyol concentrationsand unsaturated membrane lipids as well as secretion of antifreeze proteins andenzymes active at low temperatures. A combination of these mechanisms is neces-sary for the psychrotroph or psychrophile to function. Ecological mechanisms for sur-vival might include cold avoidance; fungal spores may germinate annually in spring andsummer, so avoiding the coldest months. Whether spores survive over winter or aredispersed from elsewhere is unknown. There are also few data on persistence ofbasidiomycete vs microfungal mycelia and on the relationship between low tem-peratures and the predominance of sterile mycelia in tundra soils. Acclimation of my-celia is a physiological adaptation to subzero temperatures; however, the extent towhich this occurs in the natural environment is unclear. Melanin in dark septatehyphae, which predominate in polar soils, could protect hyphae from extreme tem-peratures and play a significant role in their persistence from year to year.

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Key words:

Arctic, Antarctic, fungi, psychrophile, psychrotroph, adaptation, survival.

Introduction

In 1967, Farrell and Rose wrote ‘the existence of micro-organisms that are capable of growing well at near-zerotemperatures … has been recognized for almost a century’(Farrell & Rose, 1967), although this group of microorganismswas relatively neglected until the 1950s. There are severalreasons for the continuing interest in low temperature tolerancein fungi. One is the importance of these organisms as agentsof spoilage of refrigerated and frozen foods, and a second istheir potential commercial value as sources of cold-activeenzymes (Margesin & Schinner, 1994). These cold-tolerantfungi also have a biogeographical and ecological significance.Despite the general similarities of species spectra of decomposer

microfungi between tundra and other biomes, it is the psychro-philic fungal component of some tundra areas that distinguishesthem from other ecosystems (Flanagan & Scarborough, 1974).

The physiological and ecological mechanisms in cold-tolerant fungi that permit low temperature growth are still notfully understood (Russell, 1990; Smith, 1993; Cairns

et al.

,1995b; Snider

et al.

, 2000; Weinstein

et al.

, 2000), and havenot been previously reviewed. Russell (1990) discussed mainlythe biochemistry of adaptations of microorganisms to lowtemperatures with largely bacterial examples, whereas theaim here is to review the now quite large number of examplesof growth and activity of Arctic and Antarctic fungi atlow temperatures, and to outline the possible physiologicaland morphological mechanisms underlying fungal survival

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at such temperatures. This paper is also unique in collatingexamples from the Arctic and the Antarctic.

Definitions

In this review, the definitions of psychrophiles and psychro-trophs follow those of Morita (1975) and Gounot (1986),developed mainly with reference to bacteria. Both psychro-philic and psychrotrophic fungi have the ability to grow at0

°

C. Psychrophilic fungi have an optimum temperature forgrowth of

c

. 15

°

C or lower, and a maximum temperature forgrowth of 20

°

C or below, whereas psychrotrophic fungi havea maximum temperature for growth above 20

°

C.Biologists generally accept the definition of the Arctic

as those lands beyond the climatic limit of trees (Bliss &Matveyeva, 1992). Terrestrial ecosystems in Antarctica includea great variety of habitats from ice-free areas of the continentto the comparatively warm sub-Antarctic. Antarctic latit-udes are colder than their equivalent northern counterparts(Convey, 1996), especially in summer. The cold Arctic consistsof the northern fringes of Ellesmere Island and its ‘neighbours’,Svalbard, Franz Joseph Land, Novaya Zemlya and the NewSiberian Islands, all in the region of 80–85

°

N, whereas thecomparable cold (or maritime) Antarctic comprises the west-ern side of the Antarctic Peninsula and islands of the ScotiaArc (South Shetland, South Orkney and South SandwichIslands) at only 55–68

°

S. The remainder of the Antarcticland mass falls within the continental zone, which has mean

monthly temperatures only rarely and locally exceeding 0

°

Cin summer (Lewis Smith, 1984; Convey, 1996). A large pro-portion of the relatively small ice-free area of continental Ant-arctica consists of cold deserts, where microbial communitydevelopment is mainly restricted to three types of habitat:endolithic communities inside rocks, freshwater communitiesin transient water bodies, and hypersaline ice-covered lakes(Wynn-Williams, 1990). These continental desert communit-ies are not considered further here. There are no comparableterrestrial ecosystems in the Arctic, although similar temper-atures are experienced on nunataks in the Greenland icecap(Convey, 1996). The current review encompasses studies ofmycorrhizal and filamentous decomposer fungi plus yeastsfrom cold Arctic and Antarctic environments, thereforeincluding basidiomycetes, ascomycetes and microfungi (butnot lichenized fungi). The range of temperatures experiencedin examples of cold Arctic and maritime Antarctic environ-ments is shown in Fig. 1.

Examples of growth, activity and viability of fungi at low temperatures

Psychrotophs

The majority of isolates tested for growth, activity andviability appear to be psychrotrophic (Table 1). Latter & Heal(1971) showed that strains from a single fungal species maydiffer in their physiology depending on their climatic origin.

Fig. 1 Temperatures in examples of cold Arctic and maritime Antarctic environments. (a) Mean daily September 1993 to July 1994 soil temperatures at 3 cm depth at a polar semi-desert site at Ny-Ålesund, Svalbard, Norway, 79°N (after Coulson et al., 1995) (b) Daily surface soil temperature ranges (maximum and minimum values) during 1987 in the centre of a polygon at Jane Col, Signy Island, South Orkney Islands, 60°S (Davey et al., 1992).


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Table 1

Examples of growth, activity and viability of fungi at low temperatures

TaxonTest temperature (

°

C) Psychrophile/psychrotroph? Isolation site Type of experiment Reference

A. Examples of ‘growth’ experiments

(1) Arctic sites54 isolates, mainly mitosporic fungi Growth at 0 and 25, mainly

psychrotrophicBarren soils, Franz Joseph Land, 79

°

50’ to 81

°

50

′

NMalt extract agar medium Bergero

et al . (1999)

Phoma herbarum

Growth at 2.5–20 Higher growth rate at 2.5 than 5, psychrotrophic

Soil, Truelove Lowland, Devon Island Canada, 75

°

33

′

N, 84

°

40

′

WSand + glucose-mineral agar medium

Widden & Parkinson (1978)

(2) Antarctic sites31 isolates, mainly mitosporic fungi Growth at 4 and 35. All isolates grew

at 4, most optima at 15 or 20, mainly psychrotrophic

Plant and soil, Subantarctic Macquarie Island (55

°

30

′

S, 158

°

57

′

E); Antarctic Casey Station (64

°

17

′

S, 100

°

32

′

E)

Tomato agar medium, Lilly & Barnett’s synthetic medium

Kerry (1990)

Humicola marvinii

Growth at –2.5, optimum at 15, no growth at 20–22, psychrophilic

Fellfield soils, Signy Island, 60

°

43

′

S, 45

°

38

′

WMalt extract + mycological peptone nutrient agar medium

Weinstein

et al

. (1997)

14 taxa, mainly mitosporic fungi All grew at 1, no higher temperatures tested, pyschrophilic/psychrotrophic?

Soil, Signy Island, 60

°

S, 45

°

W Czapek Dox + trace elements agar medium

Latter & Heal (1971)

35 isolates, mainly mitosporic fungi Growth at 0–35, 33 strains grew at 5, 31 strains grew at 0. Most optima at 15 or 20, mainly psychrotrophic

Mainly soil and moss, Victoria Land, 72

°

30

′

S to 77

°

52

′

SPotato dextrose agar medium Zucconi

et al

. (1996)

B. Examples of ‘activity’ experiments

(1) Arctic sites

Phialophora hoffmanni

Cladosporium cladosporioides

Occurs at 1, optima between 18 and 20+, psychrotrophic

Soil and litter, Point Barrow, 71

°

17

′

N, 156°41

′

W

in vitro

pectinase activity Flanagan & Scarborough (1974)

Geomyces pannorum

Occurs at –4, optima at 5, psychrophilic Soil and litter, Point Barrow, 71

°

17

′

N, 156°41

′

W

in vitro

cellulase activity Flanagan & Scarborough (1974)

(2) Antarctic sites

Verticillium lecanii

Active at 5, 15 and 25, psychrotrophic Moss samples in continental Antarctica

in vitro

chitinase activity Fenice

et al

. (1998)

C. Example of ‘viability’ experiment from an Antarctic site

Soil fungi Greater number of colonies when plates incubated at 10, rather than 25, psychrotrophic?

Six sites at Signy Island, 60

°

S, 45

°

W Soil dilution and Warcup plates Bailey & Wynn-Williams (1982)

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The predominance of psychrotrophy, rather than psychrophily,in Arctic and Antarctic environments may be because, whilethese fungi still have the ability to grow around 0

°

C, tem-peratures of substrata at some times of the year are muchhigher than low air temperatures. For example, Möller &Dreyfuss (1996) wrote ‘Although average air temperatures inthe maritime Antarctic are around freezing point, local soiltemperatures and microclimates may rise to 15

°

C throughsolar radiation’. Thus a relatively small percentage of fungalstrains, estimated to be 10–20% of fungal species and strainsfrom Alaskan tundra sites (Flanagan & Scarborough, 1974),and 10% of tested isolates from two Antarctic sites on KingGeorge Island, South Shetlands, Antarctica (Möller & Dreyfuss,1996), appears to be truly psychrophilic. The low proportionof psychrophilic isolates in the strict sense from Arctic andAntarctic environments may be because the isolations havenot been performed in winter when low temperatures prevail,or have not been performed from substrata experiencingsolely low temperatures.

An important point to note when obtaining fungal speciesfrom low temperature environments is that the isolation tem-perature may bias their frequency of isolation. Very differentmicrofungal species spectra were obtained from forest soilsin Rhode Island when two different isolation temperatures(0 and 25

°

C) were used (Carreiro & Koske, 1992). Mostfungi isolated at 0

°

C were psychrotrophs, although somepsychrophiles, mostly

Mortierella

and

Mucor

spp., were alsoisolated. Isolations at 25

°

C resulted in mostly mesophileswith growth minima between 5 and 10

°

C and maxima above25

°

C. Cold temperature also appeared to have a selectiveeffect on

Geomyces pannorum

because the isolation frequencyincreased as incubation of the soil and agar plates approached0

°

C (Ivarson, 1973).

Physiological effects of low temperature and freezing on fungi

Low temperature is a relative term (Smith, 1993). In biologyit is usually identified with subzero temperatures with a lowerlimit of –70

°

C, below which no life processes persist. FromFig. 1 it is apparent that the examples chosen can be definedas low temperature environments. Soil temperatures at 3 cmdepth at a polar semi-desert site in Ny-Ålesund, Svalbard,Norway (78

°

56

′

N, 11

°

50

′

E) were below zero for 272 days,with minimum monthly winter temperatures ranging from–5.6 to –25.0

°

C (Coulson

et al.

, 1995, Fig. 1a). Summertemperatures are likely to be more conducive to fungalgrowth, since at 5 cm depth, mean, minimum and maximumsummer soil temperatures at a similar site were 6.1, 1.4 and11.4

°

C (Wookey

et al.

, 1993). Similarly, mean daily soilsurface temperatures at Jane Col, Signy Island (60

°

43

′

S,45

°

38

′

W) were below zero for a large part of the year(Fig. 1b), with 25 freeze-thaw cycles per annum. At 3 cmdepth, the lowest monthly minimum temperature in the

same polygon centre was –7.6

°

C in July, August and Octo-ber (Davey

et al.

, 1992).Cooling to low temperatures reduces the rate at which

chemical reactions occur, increases the viscosity of water,denatures protein and increases the relative permittivity ofwater thus reducing attraction between ions of oppositecharge, and markedly affecting acidic and basic residues ofproteins. In relation to the lower growth temperature limit ofpsychrophiles, there are no substantiated reports of microbialgrowth at temperatures below –12

°

C, which is consistentwith the known physical state of aqueous solutions at subzerotemperatures (Russell, 1990; Mazur, 1980). Dilute aqueoussolutions will generally supercool to –10

°

C, occasionally to–20

°

C, and most cells remain unfrozen at –10 to –15

°

C eventhough these temperatures are 9–14 degrees below the freez-ing point of their cytoplasm and there is extracellular ice in thegrowth medium. Nucleation of the supercooled cytoplasmicwater does not occur above this temperature because smallice-nuclei are barred from entering the cell by the plasmamembrane. Supercooled water has a higher vapour pressurethan that of extracellular ice, so water will move out of the cell,thereby concentrating the intracellular milieu. At temper-atures below –10 to –15

°

C, the cell water begins to freeze,further concentrating intracellular salts up to 3 molal. Theresulting ionic imbalance, altered pH and lowering of wateractivity have a toxic effect on the microorganism, which willeither prevent it from functioning or possibly kill it. Thusthe lower growth temperature limit of psychrophiles is fixed,not by the cellular properties of cellular macromolecules, butinstead by the physical properties of aqueous solvent systemsinside and outside the cell.

Cryoinjury is largely dependent on the rate of cooling, thecell type (whether it is sensitive or resistant to cold), and thecomposition of the suspending medium (Smith, 1993). Mostwork has been carried out with a view to using ultralow tem-perature for long-term preservation of viability and stability offungi, aiming to minimize the two damaging factors of dehyd-ration and intracellular freezing. Early studies established thatslow cooling in the presence of a cryoprotectant such as glycerolor dimethyl sulfoxide (DMSO) and storage at temperaturesbelow –139

°

C, quite often in liquid nitrogen or the vapour aboveit, gave best results when applied routinely (Smith, 1993).

Environmental factors related to low temperature: freeze-thaw and desiccation

It may not be adaptation to low temperature

per se

whichinfluences fungal survival in such environments but rather, forexample, to freeze-thaw cycles or desiccation. Temperaturefluctuations around 0

°

C are characteristic of the substrataof Arctic and Antarctic environments. Indeed, Coulson

et al

. (1995) found that at 3 cm depth in a high Arctic polarsemi-desert soil, 30 freeze-thaw cycles occurred during winter.Vishniac (1996) stated ‘Many investigators have examined


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the ability of their filamentous isolates to grow at near freezingtemperatures, but not their ability to survive freeze-thawing.It is generally thought that unprotected hyphomycete hyphaedo not survive freezing, while spores often do’. By contrast,Lyakh

et al

. (1984), cited in Wynn-Williams (1990), haveshown that after periodic freezing to –13

°

C and thawing theAntarctic yeast

Nadsoniella nigra

var.

hesuelica

, 33% of thepopulation was viable after one cycle and 10% was still viableafter 10 cycles.

Desiccation is possibly as important an influence on sur-vival as low temperatures, and the adaptations to both factorsmay be similar. Water (and substrate) availability rather thantemperature is reported to regulate microbial activity in themaritime and sub-Antarctic (Wynn-Williams, 1990). Simi-larly, continental Antarctica is a cold desert and free water isonly present intermittently (McRae & Seppelt, 1999).

Physiological mechanisms of cold tolerance

Several physiological mechanisms of cold-tolerance by fungihave been proposed, and it is possible that a combination ofthese strategies is employed. For example, Table 2 shows aselection of characteristics that would be advantageous to soilorganisms for winter survival in Arctic soils (Hodkinson &Wookey, 1999), and it is likely that physiological mechanismsconferring these characteristics occur in fungi.

Trehalose and cryoprotectant sugars

Trehalose is an important storage compound in fungalvegetative cells and spores (Lewis & Smith, 1967), and is themost widely distributed disaccharide in fungi (Thevelein,1984). In fungal vegetative structures, trehalose is usuallyfound together with sugar alcohols and glycogen. This alsooccurs in reproductive structures, but in this case trehaloseis often present in much higher concentrations than otherstorage carbohydrates (Thevelein, 1984). According to Cooke& Whipps (1993), trehalose appears to be a general stressprotectant in the cytosol, and it is known to stabilizemembranes during dehydration (Goodrich

et al.

, 1988).More recently, several authors have also shown accumulations

of trehalose in fungal hyphae in response to low temperatures

.

Concentrations of trehalose were shown to double in excisedalpine mycorrhizal roots when they were exposed to low tem-peratures (Niederer

et al.

, 1992) and comparative studies ofarctic and temperate strains of

Hebeloma

spp. have indic-ated substantial accumulations of trehalose in the arcticspecies when grown at low temperature (Tibbett

et al.

,1998a). Similarly,

Humicola marvinii

, a psychrophile, isolatedfrom fellfield soil at Jane Col, Signy Island in Antarctica,grown at 5

°

C and 15

°C in liquid medium accumulatedtrehalose intracellularly to a greater extent at 5°C than at15°C (Weinstein et al., 2000). In the same study, Mortierellaelongata, a psychrotrophic fungus isolated as above andincubated at 5°C, showed intracellular trehalose concentrationswhich were increased by 75% compared with incubation at15°C (Weinstein et al., 2000).

Polyols

Glycerol and mannitol may increase in concentration tomaintain turgor pressure against heat-mediated decreases inexternal water potential (Cooke & Whipps, 1993). Mannitolis thought to be important in protection against water stress(Lewis & Smith, 1967), and may be a cryoprotectant(Weinstein et al., 1997). Jennings (1984) thought of polyolsas ‘… acting as “physiological buffering agents” [in fungi] inthat they … probably maintain a suitable milieu for enzymeactivity’. Evidence for a potential cryoprotectant role ofpolyols comes from a study by Weinstein et al. (1997), usingan Antarctic isolate of Humicola marvinii compared with H.fuscoatra which had been isolated from Gossypium sp. andpurchased from a culture collection. In still liquid cultureincubated for 8 wk at 15°C, the quantity of total sugarsproduced by the two isolates was not significantly different.However, the amounts of individual sugars and polyolsproduced by the two species differed greatly (Table 3). Theclearest differences were in mannitol, known for its cryo-protectant properties, which was found at high levels in

Table 2 Ecophysiological characteristics of Arctic soil organisms exhibiting good winter survival (Hodkinson & Wookey, 1999)

Winter survival – high survival characteristics

Capacity to dehydrateProduce antifreezesHigh supercooling activityHigh chill toleranceFreeze toleranceBehavioural selection of microhabitatLive in habitats with snow coverSurvive anoxia (being encased in ice)

Table 3 Polyol and sugar production (mg–1 100 mg d. wt) produced after 8 wk at 15°C by Humicola marvinii isolated from maritime Antarctic soil, and Humicola fuscoatra isolated from Gossypium and bought from a culture collection (Weinstein et al., 1997). Differences in polyol and sugar production by the two fungi are statistically different at the 99.8% confidence level in all cases

Polyol/sugar H. marvinii H. fuscoatra

Glycerol 0.35 0.80Erythritol 0.27 0.11Trehalose 7.76 4.51Mannitol 41.07 0.51Glucose 0.18 8.07Fructose Not detected 5.03Arabitol 0.21 Not detected


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H. marvinii but which was scarce in H. fuscoatra. Conversely,H. fuscoatra produced glucose and fructose, compounds notknown for their cryoprotectant properties, while H. marviniiproduced no fructose and very little glucose.

Lipids/fatty-acids

There is considerable evidence to suggest that membranecomposition can determine the ability of fungi to grow overspecific temperature ranges (Cooke & Whipps, 1993). Thestructure and composition of membranes is likely to affect thetemperature at which their properties change from an inact-ive gel phase to an active, crystalline phase. In psychrophilicyeasts, for example species of Candida, Leucosporidium andTorulopsis, constituent fatty acids are more unsaturated thanthose of mesophiles and lowered incubation temperaturesincrease this degree of unsaturation (Kerekes & Nagy, 1980).A similar pattern of change has also been found for someMucor species (Dexter & Cooke, 1984a,b). However, withother Mucor species, membrane phospholipids rather thangeneral fatty acids (which can include storage lipids) differbetween psychrophiles, mesophiles and thermophiles (Hammonds& Smith, 1986), with levels of membrane phospholipidunsaturation decreasing from psychrophile, to mesophile tothermophiles. Proteins and sterols within membranes can alsoinfluence their stability (Dexter & Cooke, 1985).

Experimental evidence for an increase in unsaturated lipidcontent with low temperature is provided by Weinstein et al.(2000). A psychrotrophic isolate of Geomyces pannorumgrown at 5°C exhibited altered lipid composition comparedwith the same isolate grown at 15°C, with increases in unsatur-ated lipid content and overall unsaturation index. Mortierellaelongata, also grown at 5°C in the same study, showed anabsence of detectable ergosterol but presence of stearidonicacid, a fatty acid only previously reported in another speciesof psychrotrophic zygomycete (Weinstein et al., 2000). Snowmoulds, which are pathogenic to winter cereals and ley grassin taiga and boreal zones characterized by a persistent snowcover on frozen soil throughout the winter and temperaturesin the range –3 to +3°C (Jamalainen, 1974; Gaudet et al.,1999), must also have mechanisms to maintain the fluidity oftheir membrane structures and thereby grow actively at lowtemperatures. Since membrane fluidity varies with the degreeof unsaturation of lipids, the abundance of polyunsaturatedfatty acids (18 : 2 and 18 : 3) among the phospholipids ofMicrodochium nivale would enhance the ability of the organ-ism to survive at lower temperatures (Istokovics et al., 1998).

Antifreeze proteins

Extracellular and intracellular antifreezes may allow fungi tobe active at subzero temperatures and they may slow thegrowth of ice if crystallization does occur. Fungi require themaintenance of an aqueous environment for growth to secrete

enzymes and absorb carbon and nutrients. Moreover anti-freezes may be essential for inhibiting the recrystallizationof ice and promoting fungal survival through freeze-thawcycles. In addition to preventing hyphae from freezing attemperatures just below zero, antifreezes produced by fungimay keep substrates from freezing since these compoundswould be otherwise unavailable for use (Snider et al., 2000).Antifreeze proteins (AFPs), which are thought to contributesignificantly to survival at subzero temperatures by modifyingthe growth of ice, are found in bacteria (Xu et al., 1997),plants (Sidebottom et al., 2000), invertebrates (Duman et al.,1991) and fish (Griffith & Ewart, 1995). Although thereappear to be no reports to date of AFPs or antifreeze activityin fungi from cold Arctic and Antarctic environments, an AFPshowing epitopic homology to one found in the Atlanticwinter flounder, was found in the hyphae of three psychro-philic snow moulds, the ascomycete Sclerotinia borealis,and two basidiomycetes, Coprinus psychromorbidus and Typhulaincarnata (Newsted et al., 1994). However, the proteins fromthis study do not appear to have been characterized morefully, and the best recent evidence of antifreeze activity insnow-mould fungi comes from the work of Snider et al. (2000),from which the following information is taken. Isolates ofTyphula incarnata, T. ishikariensis and T. phacorrhiza showedantifreeze activity in all fractions (the growth mediumof 2% malt extract broth, the soluble hyphal fraction, andthe insoluble hyphal fraction). No antifreeze activity wasfound in isolates with peak growth temperatures above 14°C(M. nivale, S. borealis and S. homeocarpa), whereas anti-freeze activity was detected in isolates with peak growthtemperatures at 4, 10 (Typhula species), or 14°C (Coprinuspsychromorbidus). The antifreeze activity found in the growthmedium of T. phacorrhiza isolate Tp94614 was shown toarise from protein molecules. The ice crystal structuresassociated with snow mould species showed differentgrowth patterns from those previously observed, which sug-gests that these AFPs may bind to different planes of the icecrystal lattice than those found with AFPs from fish, insectsand plants.

Enzyme activity at low temperatures

The growth of psychrotrophs and psychrophiles at lowtemperatures has led to the search for enzymes with psy-chrophilic or ‘cold active’ properties (Cairns et al., 1995b),and conversely isolation of cold-active enzymes may alsocontribute to an understanding of how these fungi thrive atlow temperatures (Weinstein et al., 2000). From a furtherecological viewpoint, interest in ‘cold active’ enzymes has beenspurred by the fact that low diversity of fungal species in soilsin continental Antarctica (McRae & Seppelt, 1999) and sub-Antarctic islands (Steiman et al., 1995) is hypothesized to beoffset by a wide variety of enzymes produced by each species(Fenice et al., 1997).


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The following section concerns examples of cold-activeenzymes found in decomposer and mycorrhizal fungi in coldArctic and Antarctic environments. Enzyme activity has beenfound at low temperatures in soil fungi isolated from Antarc-tica. In a study by Weinstein et al. (1997), using the psy-chrophile Humicola marvinii isolated from fellfield soil inAntarctica and H. fuscoatra isolated from the rhizosphere ofGossypium sp. in Nigeria, H. marvinii was capable of solubil-izing inorganic phosphate and producing extracellular pro-tease enzymes in agar media at 15°C, whereas H. fuscoatrawas not. Using similar plate-screening techniques on soil fungi,33 strains (23 mitosporic fungi, three ascomycetes, three sterilemycelial strains and four yeast or yeast-like fungi) isolatedfrom different sites on Victoria Land, continental Antarctica,were tested for their ability to produce 12 extracellularenzymes at the relatively high temperature of 25°C (except forprotease at 20°C), or at the species’ optimum growth temper-ature if not 25°C (Fenice et al., 1997). Lipases were generallypresent, and in high quantities in almost all strains. Polygalac-turonase, as well as amylase and phosphatase, was common.Glucose oxidase, protease and DNAase appeared to be gener-ally low or absent.

The optimum temperatures for phosphatase and proteo-lytic activity by Arctic strains of fungi of an ectomycorrhizalgenus Hebeloma have been characterized in an excellent seriesof papers by Tibbett et al. (1998a,b, 1999). Twelve Hebelomastrains, two from arctic tundra in Svalbard, seven from nearFairbanks, Alaska, two from French forests and one fromScottish forest were tested for phosphatase activity (Tibbettet al., 1998a). At temperatures lower than or equal to 12°C,arctic strains produced more extracellular and wall-boundacid phosphatase, yet grew more slowly than the temperatestrains. The authors suggested that low growth rates in arcticstrains may be a physiological response to cold wherebyresources are diverted into carbohydrate accumulation forcryoprotection. At near freezing temperatures, increasedextracellular phosphatase production may compensate for aloss of enzyme activity at low temperature and serve to hydro-lyse organic phosphorus in frozen soil over winter. In a sec-ond, related, paper, Tibbett et al. (1998b) grew Hebelomastrains of arctic and temperate origin at 22°C or 6°C, whichwere assayed for wall-bound and extracellular acid phospho-monoesterase (PNPPase) across a temperature range of 2–37°C. Only when grown at 6°C was a cold-active extracellularPNPPase induced in all the arctic strains and most of the tem-perate strains tested. Such enzymes are suggested to be anadaptation to low soil temperatures and may allow ectomyc-orrhizas access to soil PO4

3– monoesters at low temperatures.Cold-active proteases were also found to be produced instrains of Hebeloma representative of different climatic zonesgrown in axenic culture at either 2°C and 22°C or 6°C and22°C (Tibbett et al., 1999). Culture filtrates were assayedbetween 0 and 37°C for proteolytic activity, with growth atlow temperature inducing greater activity. Many of the strains

produced protease(s), which retained significant activity attemperatures as low as 0°C, and had a thermal optimumbetween 0 and 6°C with a second optimum at a higher tem-perature. The results suggest the potential exists for continuednutrient acquisition by ectomycorrhizal fungi at low temper-atures, since while ectomycorrhizal fungi remain viable below0°C, their growth must be severely limited by the subzerotemperatures and would be physically constrained in the fro-zen bulk soil.

From this account it is apparent that enzymes active atmoderately low temperatures are produced by species ofdecomposer and mycorrhizal fungi from cold Arctic and Ant-arctic environments.

Do the properties of psychrophilic enzymes explain physiological psychrophily?

Cairns et al. (1995b) stated that, while there are examples ofenzymes which exhibit impaired function at low temperatures,it appears that activity at 0–15°C at correspondingly loweredrates is common to many enzymes from all sources, psy-chrophilic and otherwise. The properties of these enzymescould maintain the metabolic fluxes necessary for reducedgrowth rates at low temperatures and explain this feature ofpsychrophily. Conversely, enzymes from psychrophiles showthresholds of thermal inactivation of 28°C and optimumtemperatures for catalysis of 40–60°C. These temperaturesdo not match and cannot explain the low optimum temperaturefor psychrophilic growth of 9–12°C. Cairns et al. (1995b)also wrote that the invertase from the snow-mould M. nivalisshowed no specifically cold-active properties and resembledinvertases from mesophiles in all respects examined. Takentogether with the growth data, a picture emerged of thisspecies as a generally metabolically mesophilic organism.From the enzymological perspective, according to Cairnset al. (1995b), this also appears to be generally true of enzymesisolated from psychrophiles so far. For example, although30% of the maximum activity of a polygalacturonase of thepsychrophilic snow mould fungus Sclerotinia borealis wasobserved at 5°C, the optimum temperature for activity was40–50°C (Takasawa et al., 1997). The same mesophilicphenomenon is exhibited by a purified chitinase of Verti-cillium cfr. lecanii A3, isolated from continental Antarctica.The enzyme was active over a broad range of temperatures(5–60°C), and although at 5°C its activity was still 50% ofthat recorded at the optimal temperature, this was relativelyhigh at 40°C (Fenice et al., 1998).

Against this metabolically mesophilic background, spe-cific psychrophilic character (low optimum temperature forgrowth) must be conferred by some, potentially as few as one,temperature-sensitive limiting factors which inhibit growthabove the low optimum. The factors conferring low optimumtemperature for growth remain to be identified, but could, forexample, be the loss of vital properties of intracellular proteins


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just above the upper limit of fungal growth (Cairns et al.,1995a; Hoshino et al., 1997). The available evidence doesnot implicate any enzyme as the sole determinant of obligatepsychrophily, or psychrotrophy.

The above discussions of trehalose, polyols, lipids and pro-teins show that there is not one single mechanism which leadsto tolerance of low temperatures by fungi (Weinstein et al.,2000). All the cell components of a psychrophile or psy-chrotroph must be functional for the fungus to grow at lowtemperatures, and cold adaptation must be an overall cellularphenomenon (Russell, 1990). By contrast, the upper growthtemperature limit of psychrophiles and psychrotrophs canresult from the lack of activity of a single enzyme.

It would be expected that, if the changes in cell constituentsoutlined above are adaptations to cold temperatures, therewould be a seasonal pattern in these cell constituents. Thereare few studies at this fine scale, with the notable exception ofMontiel (2000) who followed the concentrations of lowmolecular weight carbohydrates in winter, spring and summerfrom one alga, three mosses and three lichens. Seasonalchanges in total soluble carbohydrate concentration wereobserved in all species. In most cryptogams exhibiting seasonalchange, concentrations of soluble carbohydrates were higherin spring relative to winter. Montiel (2000) hypothesizedthat the relatively high concentrations of carbohydratesfunction as osmolytes in winter and physiological bufferingagents in spring. No information was provided for free-livingfungi.

Ecological mechanisms of cold avoidance and cold tolerance

Fungal survival in Arctic and Antarctic environments mayoccur because of cold avoidance, rather than cold tolerance.One method of cold avoidance would be for fungi to re-establish annually in spring or summer from spores in coldArctic and maritime Antarctic areas, once the coldest periodof the year has passed. This strategy may be of little benefitin continental Antarctica as positive air temperatures areexperienced only rarely and locally, and at inland sites themean daily temperature rarely rises above –10°C (Convey,1996), although soil temperatures may be considerably higherthan those recorded in air for brief periods.

Re-establishment every year from spores – cold avoidance rather than cold tolerance?

Bergero et al. (1999) stated that the major component of anArctic soil mycoflora should be active in one or more shortgrowing seasons interspersed with periods of prolongeddormancy. They thought only a minor component, such asthe small group of psychroligotrophic fungi found in theirstudy, may be expected to show continuous slow growth.Working with Antarctic fungi, Vishniac (1996) wrote ‘It is

generally thought that unprotected hyphomycete hyphae donot survive freezing, while spores often do’. However, there islittle work on whether fungi in Arctic and Antarctic soils andlitter do re-establish annually from spores. It may be that thisis a strategy used by microfungi, rather than basidiomycetes,to avoid periods of extreme winter cold. Also, there are fewdata on the longevity of basidiomycete mycelium over winteror several seasons, and there is little information on annualrecruitment from basidiospores. Referring to basidiomycetemycorrhizas ‘Arctic and alpine environments probably selectfor traits such as longevity and mycelial spread of individualfungal genets’ (Gardes & Dahlberg, 1996), although signi-ficant recruitment from spores is suggested by the work ofMatsumoto & Tronsmo (1995) concerning a basidiomycetesnow mould, Typhula ishikariensis from Norway. The popu-lation structures of this fungus at 23 sites in meadows andpastures were determined, based on vegetative compatibilitygroup. Except for two sites dominated by a single largevegetative incompatibility group, populations were generallydiverse, regardless of the cropping history of the site.

Would these spores be able to survive low temperaturesduring winter to be able to act as a ‘reservoir’ to germinateduring spring? In temperate agricultural soils AM fungi arethought to survive adverse environmental conditions as spores(Addy et al., 1997), although these authors showed thathyphae of Glomus spp. retained their infectivity followingprolonged freezing and that spores were not an effectiveinoculum in bioassays. Gams & Stalpers (1994) stated,

‘From cryobiological experience … we know that temperaturesbetween 0 and –40°C are not suited for long-term preservationof fungi. In a moist environment the surrounding water willfreeze between 0 and –10°C. When a thin layer of water with ahigh osmotic value remains present, the spore will dehydrate. Inthis condition it can survive for several years, but at temperaturesabove –40°C there is still some metabolic activity and damagewill occur to proteins and membranes. When spores freeze in dryconditions and no dehydration occurs, ice crystals will forminside the spores at temperatures between –20 and –40°C. Thesecrystals will increase in size and the resulting damage is usuallylethal … It is only at temperatures of liquid nitrogen or at least–130°C that a permanent preservation of living fungal materialis now possible, and only after a carefully determined freezingprotocol. While under dry conditions spores of Chaetomiumand some other ascomycetes, and also conidia of genera likeAspergillus and Penicillium are known to survive for somedecades’.

Seeming to contradict Gams & Stalpers’ (1994) abovestatement that it is unlikely that frozen spores would survivesubzero temperatures in the long term, viable fungi wererecovered from all sections of Greenland ice-cores studied byMa et al. (2000). Most isolates were recovered from 300- and500-yr-old sections, and only a few from 600 to 140 000 yrbefore present. Thus, survival of viable spores is uncertain at


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the subzero temperatures experienced in cold Arctic andAntarctic environments.

Are these spores dispersed from elsewhere?

A further cold avoidance mechanism used by fungi in Arcticand Antarctic environments could be re-colonization inspring from spores, or hyphal fragments, dispersed fromwarmer climates elsewhere. According to Vishniac (1996), theproblem of determining which fungi are indigenous isparticularly troublesome with regard to the hyphomycetesreported from continental Antarctica, as these fungal sporesare readily airborne. Are there enough spores transported inspring and summer from continental America each year toAntarctica, or from more temperate climates to the Arctic, toreplace dead ‘frozen’ mycelia or spores? Marshall (1997) foundspores of several fungi not normally native to Antarctica in airsamples collected at Signy Island in the maritime Antarctic.Their presence was associated with a specific weather pattern,occurring with an estimated mean annual frequency of 1.5,which allowed wind-borne transfer of exotic biologicalparticles to Antarctica from South America. Evidence fromthe occurrence of fungal propagules in the air suggested thatmost fungi that produce spores on Signy Island disperse theirspores during the summer. Chlamydospores were exceptionalin being dispersed in winter. These spores are much moreresilient to stress than most, having thick pigmented walls andare therefore better protected to survive extreme cold ofwinter and the increased levels of UV radiation associatedwith ozone depletion. Marshall (1998) continued his researchon the origin of fungal propagules at Signy Island by swabbingskuas to obtain keratinophilic fungi when they returned earlyin summer. Geomyces pannnorum was recovered in culturesuggesting that these birds may act as vectors for the transportof microorganisms between Antarctica and more northernlandmasses.

These results show that fungal spores are dispersed fromelsewhere to Antarctica, and a similar pattern of transport ofexotic airspora has been found at sites in the Arctic, althoughtotal concentrations of propagules were low in both the mari-time Antarctic (Marshall, 1997) and the Arctic. Sampling ofairborne pollen and spores at Ny-Ålesund on Svalbard in thesummer of 1986 revealed only very low concentrations of airspora (Johansen & Hafsten, 1988). The maximum diurnalconcentration of Cladosporium was merely 44 spores m–3 air,although of the fungal spores less than 2% belonged toCladosporium spp. (the rest were unidentified). The maximumconcentration measured in Tromsø, northern Norway, thatseason was about 80 and in Bodø about 600 spores m–3. Thetendency towards increased concentration of Cladosporiumspores during episodes of exotic pollen recording indicatedthat this spore type is subject to long-distance dispersal,perhaps from central Finland. Similarly, a survey of airsporacollected on Jan Mayen between 24 April and 31 August

1988, revealed only very small concentrations ( Johansen,1991). The highest diurnal average of Cladosporium was 27spores m–3 air. A cumulative diurnal mean of c. 2600 fungalspores m–3 air was recorded, constituting only one third of thetotal amount obtained on Svalbard in 1986. Cladosporiumconstituted 4.7% of the total fungus record. Alternaria madeup less than 0.1% of the airborne fungal spores recordedduring the sampling period, basidiospores 11.8% and un-identified fungal spores as much as 83.5%. The majority ofthese spores were small (2–4 µm) hyaline, unicellular globosespores, and hyaline fusiform spores. Detached hyphal frag-ments occurred, hyaline septate ones being more numerousthan dematiaceous ones and conidiophores were occasionallyobserved. The levels of hyphal fragments on Jan Mayen in1988 were small compared with, for instance diurnal averageconcentrations of 10–599 fragments m–3 air above grass inEngland (Pady & Gregory, 1963, cited in Johansen, 1991).Betula pollen indicated transport from Iceland and/or NorthAmerica and Greenland.

In summary, long and short distance transport of fungalpropagules is possible although the numbers of propagules arelow. Thus, some fungi may survive in Arctic and Antarcticenvironments by avoiding the extreme low temperaturesduring winter through annual germination from airsporaduring spring and summer. There is evidence, however, fromair samples of marked seasonality in spore dispersal. At theSvalbard site, spores of Cladosporium and other unspecifiedfungal taxa were recorded occasionally or very sparsely fromthe start of recording in late April and onwards, but did notbecome more frequent until the middle or later part of June.The seasonal maximum of Cladosporium spores was registered on1 August (44 spores m–3), whereas the bulk of ‘total’ fungalspores occurred after 10 August when concentrations up to600 spores m–3 were recorded. A similar pattern was observedin Jan Mayen (Johansen, 1991), with the seasonal peak infungal spores being from the middle of July to a maximum on27 August of 639 spores m–3 air. While sampling ceased on31 August, fungal spores were still observed and Johansen(1991) believed that future investigations should includeSeptember to cover the whole season before the onset of winter.However, the importance of spring and summer germinationof airspora as a cold-avoidance mechanism remains unclearsince, in most areas of the world (except Signy Island wherepeak dispersal was in early summer), peak concentrations ofCladosporium spores and other epiphytic saprotrophic fungi tendto occur at the end of the growing season, when the maximumsurface area of suitable host material is available for colonization.This is true even at high latitudes in the Northern hemispherewhere the more diverse flora and larger numbers of vascularplants produce host material in larger volumes than thecryptogam-dominated Antarctic flora (Marshall, 1997). Thus,the ‘foreign’ propagules dispersed in autumn would haveto survive the cold temperatures in winter, as would the‘native’ propagules. More research is necessary on whether


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annual seasonal germination occurs, if it is a cold-avoidancemechanism, if this occurs in both microfungi and basidio-mycetes, or if Arctic and Antarctic environments select for traitssuch as longevity and mycelial spread of individual fungalgenets of basidiomycetes.

Effect of low temperature on spore production

Despite the now relatively large number of reports of extensionrate of cold tolerant fungi at low temperatures (Table 1), thereappear to be no data on spore production by psychrotrophicand psychrophilic fungi in response to a range of temperatures.Are more spores produced by cold-adapted fungi at lowtemperatures than temperate isolates of the same species?Such studies would also be useful in understanding the roleof sterile mycelia in cold-tolerance (discussed below). In anexperiment using a temperate isolate of Penicillium hirsutumgrown on potato dextrose agar and kept at 20, 10, 4, 2, 0, –2and –4°C, sporulation and germination were retarded at lowtemperatures, and at –4°C no germination occurred (Bertolini& Tian, 1996). It is necessary to repeat this type of testfor psychrotrophic and psychrophilic fungi to see whetherincreased spore production occurs at low temperatures.

Mycelial acclimation to low temperatures in the field

From research in fungal cryopreservation, at fast rates ofcooling hyphae do not have time to lose water and freezeinternally. This is normally a lethal event (Smith, 1993). Theconventionally employed cooling rate for the cryopreservationof fungi is 1°C min–1, although this is species dependent(Morris et al., 1988; Corbery & LeTacon, 1997). Anotherexample of fungal acclimation to low temperatures in thelaboratory has been provided by Robinson & Morris (1984).Hyphae of Fusarium oxysporum f. sp. lycopersici transferredfrom 25 to 7°C and maintained at this temperature for 2 hwere more tolerant to subsequent cooling to –2°C thanhyphae that had not been pretreated in this manner. Doesthis acclimation occur in Arctic and Antarctic fungi in thefield and does it increase survival? There appear to be nodirectly relevant Arctic or Antarctic studies from thenatural environment, but some evidence is provided froman experiment using blocks of temperate field soil containingAM (arbuscular mycorrhizal) fungi which were either slowlycooled (2°C d–1 to 5°C) or held at room temperature (20°C)before freezing at –12°C (Addy et al., 1998). Infectivity ofAM fungi was greater in soil that was slowly cooled beforefreezing, hypothesized to result from cold acclimation ofextra-radical hyphae. The hypothesis was tested using in vitromycorrhizas, cultured in Petri plates with two compartmentsin which hyphae grew into a separate section. Metabolicactivity of these hyphae following freezing at –5°C wasassessed using a vital stain. The majority of cultures that wereslowly cooled as above before freezing contained active hyphae,

whereas hyphal activity was almost completely eliminated byfreezing in cultures that were not precooled. The authorsstated that, to their knowledge, this was the first report ofacclimation to cold temperatures by AM fungi. The specificmechanisms conferring freezing tolerance on AM fungiremain to be determined, and it is unclear whether thesetemperate isolates would respond to freezing as Arctic andAntarctic isolates would, or whether acclimation occurs innatural high latitude environments.

Seasonal patterns in mycelial biomass of psychrophiles and psychrotrophs

‘The biomass of psychrophiles may vary seasonally from lowvalues in spring to higher values in autumn’ (Flanagan &Scarborough, 1974). At one US tundra site, 67% of thefungal strains that grew from propagules isolated from soil inthe autumn were psychrophilic (Flanagan & Scarborough,1974). However, there are few studies concerning seasonalvalues of psychrophilic biomass from the field in cold environ-ments, or of a series of seasonal isolations and response to arange of temperatures of the fungi obtained. As Smith & Read(1997) have written, more studies through the year in thenatural environment of the fungi are much needed. They providenot only ecologically relevant information, but also valuablepointers for physiological investigations of hyphae and spores.

Other mechanisms of cold adaptation

Sterile mycelia and dark septate hyphae

Aspects of fungal life-history and morphology in Arctic andAntarctic fungi may be adaptations to cold tolerance. Examplesof abbreviated life cycles are found in fungi existing in harshenvironments, shown by the short-cycled rusts in theCanadian Arctic (Savile, 1953) and the predominance ofsterile fungi in tundra soils (Widden & Parkinson, 1979). Itis, however, not known whether these are responses to lowtemperature per se.

Fungi with dark septate hyphae dominate the soil micro-bial community in Antarctic, Arctic and alpine soils (Smith &Read, 1997). Melanins may protect dark septate hyphae fromextreme temperatures and drought, and so broaden theecological niche of these fungi (Jumpponen & Trappe,1998). These authors stated that such resistance to cold anddesiccation may play a significant role for persistence ofhyphae from year to year.

Conclusions

The majority of fungi isolated from Arctic and Antarctic soilsand litter are psychrotrophic. The physiological mechanismsconferring cold tolerance are complex and there is not onesingle adaptation as all the cell components of a psychrophile


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or psychrotroph must be functional for the fungus to grow atlow temperatures. By contrast, the upper growth temperaturelimit of cold-tolerant fungi can result from the lack of activityof a single enzyme. With respect to ‘cold active’ enzymes,while there are examples of enzymes that exhibit impairedfunction at low temperatures, it appears that activity at0–15°C at correspondingly lowered rates is common tomany enzymes from all sources, psychrophilic or other-wise. Conversely, psychrophilic fungi (defined as such bytheir low optimum temperature for growth) may producemesophilic enzymes. From an ecological viewpoint, more workis necessary on whether fungi germinate from spores annu-ally in spring and summer as a strategy to avoid the coldesttemperatures in Arctic and Antarctic environments, and thesignificance of long and short distance spore dispersal to thisstrategy is unclear. The longevity of basidiomycete myceliain Arctic and Antarctic environments through periods ofextreme cold is unknown, as is whether mycelial acclimationto low temperatures occurs in the field. More information isnecessary about the response of sporulation in cold-tolerantfungi at low temperatures, and whether sterile mycelia anddark septate hyphae, both predominant in Arctic and Antarcticecosystems, are adaptations to low temperatures.

Acknowledgements

Financial support from The Coalbourn Trust of the BritishEcological Society for the study of the ecology of Arctic sapro-trophic fungi, and from the Global Atmospheric NitrogenEnrichment Thematic Programme of the Natural Environ-ment Research Council, is gratefully acknowledged. The kindcomments of Peter D. Moore and Ron I. Lewis Smith greatlyimproved earlier drafts of this manuscript.

References

Addy HD, Miller MH, Peterson RL. 1997. Infectivity of the propagules associated with extraradical mycelia of two AM fungi following winter freezing. New Phytologist 135: 745–753.

Addy HD, Boswell EP, Koide RT. 1998. Low temperature acclimation and freezing resistance of extraradical VA mycorrhizal hyphae. Mycological Research 102: 582–586.

Bailey AD, Wynn-Williams DD. 1982. Soil microbiological studies at Signy Island, South Orkney Islands. British Antarctic Survey Bulletin 51: 167–191.

Bergero R, Girlanda M, Varese GC, Intili D, Luppi AM. 1999. Psychrooligotrophic fungi from Arctic soils of Franz Joseph Land. Polar Biology 21: 361–368.

Bertolini P, Tian SP. 1996. Low temperature biology and pathogenicity of Penicillium hirsutum on garlic in storage. Postharvest Biology and Technology 7: 83–89.

Bliss LC, Matveyeva NV. 1992. Circumpolar arctic vegetation. In: Chapin III FS, Jeffries RL, Reynolds JF, Shaver GR, Svoboda J, eds. Arctic ecosystems in a changing climate. An ecophysiological perspective. San Diego, CA, USA: Academic Press, 59–89.

Cairns AJ, Howarth CJ, Pollock CJ. 1995a. Submerged batch culture of the psychrophile Monographella nivalis in a defined medium; growth,

carbohydrate utilisation and responses to temperature. New Phytologist 129: 299–308.

Cairns AJ, Howarth CJ, Pollock CJ. 1995b. Characterisation of acid invertase from the snow mould Monographella nivalis: a mesophilic enzyme from a psychrophilic fungus. New Phytologist 130: 391–400.

Carreiro MM, Koske RE. 1992. Room temperature isolations can bias against selection of low temperature microfungi in temperate forest soils. Mycologia 84: 886–900.

Cooke RC, Whipps JM. 1993. Ecophysiology of fungi. Oxford, UK: Blackwell Scientific.

Convey P. 1996. The influence of environmental characteristics on life history attributes of Antarctic terrestrial biota. Biological Reviews 71: 191–225.

Corbery Y, LeTacon F. 1997. Storage of ectomycorrhizal fungi by freezing. Annales Des Sciences Forestières 54: 211–217.

Coulson SJ, Hodkinson ID, Strathdee AT, Block W, Webb NR, Bale JS, Worland MR. 1995. Thermal environments of Arctic soil organisms during winter. Arctic and Alpine Research 27: 364–370.

Davey MC, Pickup J, Block W. 1992. Temperature variation and its biological significance in fellfield habitats on a maritime Antarctic island. Antarctic Science 4: 383–388.

Dexter Y, Cooke RC. 1984a. Fatty-acids, sterols and carotenoids of the psychrophile Mucor strictus and some mesophilic Mucor species. Transactions of the British Mycological Society 83: 455–461.

Dexter Y, Cooke RC. 1984b. Temperature-determined growth and sporulation in the psychrophile Mucor strictus. Transactions of the British Mycological Society 83: 696–700.

Dexter Y, Cooke RC. 1985. Effect of temperature on respiration, nutrient uptake and potassium leakage in the psychrophile Mucor strictus. Transactions of the British Mycological Society 84: 131–136.

Duman JG, Xu L, Nevan LG, Tursman D, Wu DW. 1991. Haemolymph proteins involved in insect subzero temperature tolerance: ice nucleators and antifreeze proteins. In: Leed RE, Denlinger DL, eds. Insects at low temperatures. London, UK: Chapman & Hall, 94–127.

Farrell J, Rose AH. 1967. Temperature effects on microorganisms. Annual Review of Microbiology 21: 101–120.

Fenice M, Selbmann L, Zucconi L, Onofri S. 1997. Production of extracellular enzymes by Antarctic fungal strains. Polar Biology 17: 275–280.

Fenice M, Selbmann L, Di Giambattista R, Federici F. 1998. Chitinolytic activity at low temperature of an Antarctic strain (A3) of Verticillium lecanii. Research in Microbiology 149: 289–300.

Flanagan PW, Scarborough AM. 1974. Physiological groups of decomposer fungi on tundra plant remains. In: Holding AJ, Heal OW, MacLean Jr SF, Flanagan PW, eds. Soil organisms and decomposition in tundra. Stockholm, Sweden: Tundra Biome Steering Committee, 159–181.

Gams W, Stalpers JA. 1994. Has the prehistoric ice-man contributed to the preservation of living fungal spores? FEMS Microbiology Letters 120: 9–10.

Gardes M, Dahlberg A. 1996. Mycorrhizal diversity in arctic and alpine tundra: an open question. New Phytologist 133: 147–157.

Gaudet DA, Laroche A, Yoshida M. 1999. Low temperature-wheat-fungal interactions: a carbohydrate connection. Physiologia Plantarum 106: 437–443.

Goodrich RP, Handel TM, Baldeschwieler JD. 1988. Modification of lipid phase behaviour with membrane-bound cryoprotectants. Biochimica et Biophysica Acta 938: 143–154.

Gounot A-M. 1986. Psychrophilic and psychrotrophic microorganisms. Experientia 42: 1192–1197.

Griffith M, Ewart KV. 1995. Antifreeze proteins and their potential use in frozen foods. Biotechnology Advances 13: 375–402.

Hammonds P, Smith SN. 1986. Lipid composition of a psychrophilic, a mesophilic and a thermophilic Mucor species. Transactions of the British Mycological Society 86: 551–560.

Hodkinson ID, Wookey PA. 1999. Functional ecology of soil organisms in tundra ecosystems: towards the future. Applied Soil Ecology 11: 111–126.


Research review


Review352

Hoshino T, Tronsmo AM, Matsumoto N, Ohgiya S, Ishizaki K. 1997. Effects of temperature on growth and intracellular proteins of Norwegian Typhula ishikariensis isolates. Acta Agriculturae Scandinavica 47: 185–189.

Istokovics A, Morita N, Izumi K, Hoshino T, Yumoto I, Sawada MT, Ishizaki K, Okuyama H. 1998. Neutral lipids, phospholipids, and a betaine lipid of the snow mould fungus Microdochium nivale. Canadian Journal of Microbiology 44: 1051–1059.

Ivarson KC. 1973. Fungal flora and rate of decomposition of leaf litter at low temperatures. Canadian Journal of Soil Science 53: 79–84.

Jamalainen EA. 1974. Resistance in winter cereals and grasses to low-temperature parasitic fungi. Annual Review of Phytopathology 12: 281–302.

Jennings DH. 1984. Polyol metabolism in fungi. Advances in Microbial Physiology 25: 149–193.

Johansen S. 1991. Airborne pollen and spores on the Arctic island of Jan Mayen. Grana 30: 373–379.

Johansen S, Hafsten U. 1988. Airborne pollen and spore registrations at Ny-Ålesund, Svalbard, summer 1986. Polar Research 6: 11–17.

Jumpponen A, Trappe JM. 1998. Dark septate endophytes: a review of facultative biotrophic root-colonizing fungi. New Phytologist 140: 295–310.

Kerekes R, Nagy G. 1980. Membrane lipid composition of a mesophilic and psychrophilic yeast. Acta Alimentaria 9: 93–98.

Kerry E. 1990. Effects of temperature on growth rates of fungi from Subantarctic Macquarie Island and Casey, Antarctica. Polar Biology 10: 293–299.

Latter PM, Heal OW. 1971. A preliminary study of the growth of fungi and bacteria from temperate and Antarctic soils in relation to temperature. Soil Biology & Biochemistry 3: 365–379.

Lewis DH, Smith DC. 1967. Sugar alcohols (polyols) in fungi and green plants I. Distribution, physiology and metabolism. New Phytologist 66: 143–184.

Lewis Smith RI. 1984. Terrestrial plant biology of the Sub Antarctic and Antarctic. In: Laws RM, ed. Antarctic Ecology, Vol. 1. London, UK: Academic Press, 61–162.

Lyakh SP, Kozlova TM, Salivonik SM. 1984. Effect of periodic freezing and thawing of cells of the Antarctic black yeast Nadsoniella nigra var. hesuelica. Microbiology 52: 486–491.

Ma L-J, Rogers SO, Catranis CM. 2000. Detection and characterisation of ancient fungi entrapped in glacial ice. Mycologia 92: 286–295.

Margesin R, Schinner F. 1994. Properties of cold-adapted microorganisms and their potential role in biotechnology. Journal of Biotechnology 33: 1–14.

Marshall WA. 1997. Seasonality in Antarctic airborne fungal spores. Applied and Environmental Microbiology 63: 2240–2245.

Marshall WA. 1998. Aerial transport of keratinaceous substrate and distribution of the fungus Geomyces pannorum in Antarctic soils. Microbial Ecology 36: 212–219.

Matsumoto N, Tronsmo AM. 1995. Population structure of Typhula ishikariensis in meadows and pastures in Norway. Acta Agriculturae Scandinavica 45: 197–201.

Mazur P. 1980. Limits to life at low temperatures and at reduced water contents and water activities. Origins of Life 10: 137–159.

McRae CF, Seppelt RD. 1999. Filamentous fungi of the Windmill Islands, continental Antarctica. Effect of water content in moss turves on fungal diversity. Polar Biology 22: 389–394.

Möller C, Dreyfuss MM. 1996. Microfungi from Antarctic lichens, mosses and vascular plants. Mycologia 88: 922–933.

Montiel PO. 2000. Soluble carbohydrates (trehalose in particular) and cryoprotection in polar biota. Cryoletters 21: 83–90.

Morita RY. 1975. Psychrophilic bacteria. Bacterial Reviews 39: 144–167.Morris GJ, Smith D, Coulson GE. 1988. A comparative study of the

changes in the morphology of hyphae during freezing and viability upon thawing for twenty species of fungi. Journal of General Microbiology 134: 2897–2906.

Newsted WJ, Polvi S, Papish B, Kendall E, Saleem M, Koch M, Hussain A, Cutler AJ, Georges F. 1994. A low molecular weight peptide from snow mold with epitopic homology to the winter flounder antifreeze protein. Biochemistry and Cell Biology 72: 152–156.

Niederer M, Pankow W, Wiemken A. 1992. Seasonal changes of soluble carbohydrates in mycorrhizas of Norway spruce and changes induced by exposure to frost desiccation. European Journal of Forest Pathology 22: 291–299.

Pady SM, Gregory PH. 1963. Numbers and viability of airborne hyphal fragments in England. Transactions of the British Mycological Society 46: 609–613.

Robinson PM, Morris GM. 1984. Tolerance of hyphae of Fusarium oxysporum f.sp. lycopersici to low temperature. Transactions of the British Mycological Society 83: 569–573.

Russell NJ. 1990. Cold adaptation of microorganisms. Philosophical Transactions of the Royal Society London B 326: 595–611.

Savile DBO. 1953. Short-season adaptations in the rust fungi. Mycologia 45: 75–87.

Sidebottom C, Buckley S, Pudney P, Twigg S, Jarman C, Holt C, Telford J, McArthur A, Worrall D, Hubbard R, Lillford P. 2000. Heat-stable antifreeze protein from grass. Nature 406: 256.

Smith D. 1993. Tolerance to freezing and thawing. In: Jennings DH, ed. Stress Tolerance of Fungi. New York, USA: Marcel Dekker Inc, 145–171.

Smith SE, Read DJ. 1997. Mycorrhizal symbiosis, 2nd edn. London, UK: Academic Press Ltd.

Snider CS, Hsiang T, Zhao G, Griffith M. 2000. Role of ice nucleation and antifreeze activities in pathogenesis and growth of snow molds. Phytopathology 90: 354–361.

Steiman R, Frenot Y, Sage L, Seigle-Murandi, Guiraud P. 1995. Contribution à l’étude de la mycoflore du sol des Îles Kerguelen. Cryptogamie, Mycologie 16: 277–291.

Takasawa T, Sagisaka K, Yagi K, Uchiyama K, Aoki A, Takaoka K, Yamamato K. 1997. Polygalacturonase isolated from the culture of the psychrophilic fungus Sclerotinia borealis. Canadian Journal of Microbiology 43: 417–424.

Thevelein JM. 1984. Regulation of trehalose mobilisation in fungi. Microbiological Reviews 48: 42–59.

Tibbett M, Sanders FE, Cairney JWG. 1998a. The effect of temperature and inorganic phosphorus supply on growth and acid phosphatase production in arctic and temperate strains of ectomycorrhizal Hebeloma spp. in axenic culture. Mycological Research 102: 129–135.

Tibbett M, Grantham K, Sanders FE, Cairney JWG. 1998b. Induction of cold active acid phosphomonoesterase activity at low temperature in psychrotrophic ectomycorrhizal Hebeloma spp. Mycological Research 102: 1533–1539.

Tibbett M, Sanders FE, Cairney JWG, Leake JR. 1999. Temperature regulation of extracellular proteases in ectomycorrhizal fungi (Hebeloma spp.) grown in axenic culture. Mycological Research 103: 707–714.

Vishniac HS. 1996. Biodiversity of yeasts and filamentous microfungi in terrestrial Antarctic ecosystems. Biodiversity and Conservation 5: 1365–1378.

Weinstein RN, Palm ME, Johnstone K, Wynn-Williams DD. 1997. Ecological and physiological characterisation of Humicola marvinii, a new psychrophilic fungus from fellfield soils in the maritime Antarctic. Mycologia 89: 706–711.

Weinstein RN, Montiel PO, Johnstone K. 2000. Influence of growth temperature on lipid and soluble carbohydrate synthesis by fungi isolated from fellfield soil in the maritime Antarctic. Mycologia 92: 222–229.

Widden P, Parkinson D. 1978. The effect of temperature on growth of four Arctic soil fungi in a three-phase system. Canadian Journal of Microbiology 24: 415–421.

Widden P, Parkinson D. 1979. Populations of fungi in a high arctic ecosystem. Canadian Journal of Botany 57: 2408–2417.


Research review


Review 353

Wookey PA, Parsons AN, Welker JM, Potter JA, Callaghan TV, Lee JA, Press MC. 1993. Comparative responses of phenology and reproductive development to simulated environmental change in sub-arctic and high arctic plants. Oikos 67: 490–502.

Wynn-Williams DD. 1990. Ecological aspects of Antarctic microbiology. Advances in Microbial Ecology 11: 71–146.

Xu H, Griffith M, Patten CL, Glick BR. 1997. Isolation and

characterisation of an antifreeze protein with ice nucleation activity from the plant growth promoting rhizobacterium Pseudomonas putida GR12–2. Canadian Journal of Microbiology 44: 64–73.

Zucconi L, Pagano S, Fenice M, Selbmann L, Tosi S, Onofri S. 1996. Growth temperature preferences of fungal strains from Victoria Land, Antarctica. Polar Biology 16: 53–61.


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Cold adaptation in Arctic and Antarctic fungi