Abstracts / Comparative Biochemistry and Physiology, Part A 126 (2000) S1 S163 S 17

COPING WITH OSMOTIC CHALLENGES: O S M O R E G U L A T I O N T H R O U G H A C C U M U -

L A T I O N A N D R E L E A S E O F C O M P A T I B L E S O L U T E S I N B. S U B T I L I S

B r e m e r E.

U n i ve r s i t y o f Ma rbu rg , Dept . o f B i o l o g y , L a b o r a t o r y for M i c r o b i o l o g y , K a r l - v o n - F r i s c h Str., D - 3 5 0 3 2

M arbu r g , G e r m a n y ; E-mai l : b r e m e r @ m a i l e r . u n i - m a r b u r g . d e Bacteria lack systems for active water transport; therefore, cellular water content is governed by osmosis and is strongly affected by changes in environmental osmolality. Cells maintain vital turgor by dynamically modulating the pool of osmotically active solutes in their cytoplasm. To prevent the dehydration of the cytoplasm under hyperosmotic conditions, many microorganisms that do not permanently live in high osmolality habitats amass specific organic osmolytes, the so- called compatible solutes. These compounds are highly congruous with cellular functions and are accumulated by non- halophilic bacteria in preference to inorganic ions that are deleterious in high concentrations. In its natural habitats, Bacillus subtilis is frequently subjected to restrictions in the availability of water and it has consequently developed sophisticated stress response systems to cope effectively with high osmolality surroundings. An increase in the salinity of the environment triggers the induction of a large stress regulon that is under the control of the alternative transcription factor Sigma B. The SigB-controlled stress response network provides cross-protection for non-growing cells against a variety of environmental insults, including severe osmotic up-shocks. Since the induction of the SigB regulon is only transient, the general stress regulon is an inadequate defense for protecting B. subtilis cells growing for prolonged periods in osmotically adverse surroundings. Under these circumstances, the synthesis and uptake of compatible solutes play a key role in the cellular adaptation to hypertonicity and the accumulation of these compounds permit cell growth over a wide range of osmotic conditions (1). Initially, large amounts of potassium are acquired via two Ktr-type transport systems, which is then foflowed by the massive production of the osmoprotectant proline via an osmotically controlled biosynthetic pathway. In addition, B. subtilis can also synthesize the potent compatible solute glycine betaine from an exogenous supply of the precursor choline when it is osmotically challenged. Furthermore, a wide variety of preformed compatible solutes are scavenged from environmental resources through five osmotically regulated transport systems. - To prevent the bursting of the cell and to readjust turgor, these compounds are rapidly released through mechanosensitive channels when B. subtilis is suddenly exposed to an osmotic down-shock.

(1) Kempf, B. and E. Bremer (1998) Arch. Microbiol. 170:319-330.

PHOTOPERIOD, MELATONIN AND THE CONTROL OF MATURATION IN FARMED FISH Por t e r M., Randa l l C., M a g w o o d S., Fu t te r W. and B r o m a g e N.

Ins t i tu te o f Aqua c u l t u r e , Un ive r s i t y o f Stir l ing, > Stir l ing, F K 9 4 L A , Sco t l and

One of the most striking characteristics of fish is their seasonality, with the timing of developmental and maturational events dominated and in turn coordinated by the seasonal changes in daylength, temperature, food supplies, rainfall, etc. Of the series of environmental factors implicated in this control, daylength is generally considered the most important although for many fish species it is likely that an array of environmental cues rather than a single factor cooperate with for example photoperiod to synchronise developmental events. For commercial farms this seasonality is a major constraint to their all year round production of fish of consistent size and quality for the retail markets.

In this review we discuss the ways in which fish respond to environmental change and how this knowledge can be used by commercial farms to control maturation and hence spread production. Data will be presented for a range of species including salmonids, bass, cod and flatfish and will include the uses of light manipulation in sea cage culture.

We know that reproduction is profoundly affected by environmental change and that this is achieved by corresponding alterations in the activity of the GnRH-GtH-gonadal axis. However, at present the linkage between the environment and controlling neuroendocrine cascade remains unclear. There is considerable evidence for the involvement of the pineal hormone melatonin in these processes, but its role remains to be clarified. Data will be presented on how diel melatonin secretion is affected by photoperiod, temperature and other factors, how its removal or addition affects reproduction and how these might interact with endogenous circadian and circannual rhythms. Also reviewed will be recent reports of the presence of melatonin binding and receptor activity in the brain and their co-localisation with the range of neurones implicated in the control of GnRH-GtH function. This will also consider the possible relationships of the various neuroendocrine and endogenous rhythmic processes to the array of clock and other genes which are thought to be involved in the measurement and coordination of daily and calendar time. (The authors are grateful to the NERC, the EC, a BBSRC CASE award, the BTA and a number of commercial farms for supporting parts of this work).