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Chapter 20The Archaea- “ancient”
12-23-2008
Archaea
highly diverse with respect to morphology, physiology, reproduction and ecologybest known for growth in anaerobic, hyper-salineand high-temperature habitatsalso found in marine arctic temperature and tropical watersSpherical, rod-shaped, spiral, irregular or pleomorphicSingle cells or aggregated filaments (upto 200μm)
Phylogenetic relationships
Figure 20.1
Bacteria
Cell Wallslack muramic acid and D-amino acids but can be stained gram+ or gram-pseudomurein (peptidoglycan-like polymer: L-amino acids with complex polysaccharides) found in some methanogenic speciescomplex polysaccharides, proteins or glycoproteinsfound in some other species
G(+) G(-)
Fig. 3.30
Lipids and Membranes
Bacteria/Eucaryotesfatty acids attached to glycerol by ester linkages
Archaeabranched chain hydrocarbons attached to glycerol by ether linkagessome have diglyceroltetraethers
bilayer membrane
monolayer membrane
The lipids combine various way to yield membranes of different rigidity and thickness
Archaealmembranes may contain a mix of the lipids to maintain stability-
Archaealmembranes-lipids
C40 tetraethers
C20 diethers
Fig. 3.11
Geneticsbinary fission, budding, fragmentationChromosomes (variation in G/C contents- 21~ 68%)
Smaller genomes comparing to eubacteriasome have histones that bind DNA to form nucleosome-like structures
~30% of genes (code for proteins involved in transcription, translation or DNA metabolism ) shared with eucaryotesmany genes (involved in metabolic pathways) shared only with bacteria
evidence for lateral gene transfer
Molecular biology
Eukaryotic type DNAPBacterial type RNA (polygenic RNA)Eukaryotic type RNAP, promoter, and tRNARibosomes
70S (bacterial-like)shape variable, differing from both bacterial and eukaryotic ribosomes
Eukaryotic type elF2 and SRP (signal recognition particle) for protein secretion
Figure 20.2
Carrying eucaryotic type promoter
BER (B responsive element)-purine-rich region before the TATA box
Metabolismgreat variationorganotrophy, autotrophy, and phototrophyUnique glucose catabolism, pathways for CO2 fixation
Some have the ability to synthesize methane
TaxonomyTwo phyla
Crenarchaeota: “spring”“ the ancestor of the archaea? ”
Euryarchaeota: “wide”most are extremely thermophilicmany are acidophilic and sulfur dependent
Phylum Crenarchaeota
most are extremely thermophilic (70-80°C)many are acidophiles(pH 2-3)many are sulfur-dependent (solfatara)
as electron acceptor or as electron source
almost all are strict anaerobes
grow in geothermally heated water or soils that contain elemental sulfur
Figure 20.5 (a)
Two best studied Crenarchaeota
Sulfolobusirregularly lobed, spherical shaped
cell walls contain lipoproteins and carbohydrates
Thermoproteuslong thin rod, bent or branchedGlycoprotein cell wall
70-97 °CpH 2.5-6.5
Figure 20.7
Phylum Euryarchaeotainformally divided into five major groups
methanogenshalobacteria: require at least 1.5 M NaCl (8%)
H. Halobium- bacteriorhodopsins for photosynthesis
Thermoplasms: lack cell wall and grow in coal minesoptimal growth at 55-59oC (PH 1-2, even at PH 0)
extremely thermophilic S0-metabolizerssulfate-reducers
MethanogensAnaerobic environments rich in organic mater
animal rumens, anaerobic sludge digesters, within anaerobic protozoa
Ecological and practical importance
important in wastewater treatmentproduce significant amounts of methane
as clean burning fuel and energy sourcegreenhouse gas ( global warming)
can oxidize ironcontributes to corrosion of iron pipes
Methanogenesisproduce methane, a clean burning fuel and an excellent energy source
can be an ecological problem:10,000 billion tons of methane hydrate buried in the ocean floor methane consuming microbes?
Methanotrophs
Box 20.2
~100 species using fluorescent probe for
specific DNA sequencesMethane consuming Archaea surrounding by a layer of bacteria: cooperate metabolically oxidized as much as 300 million tons of methane annually
The Halobacteriaextreme halophiles (Dead sea)
require at least 1.5 M NaClcell wall disintegrates if [NaCl] < 1.5 M
growth optima ~ 3-4 M NaClaerobic, respiratory, chemoheterotrophs with complex nutritional requirements
Figure 20.12b
Halobacterium salinarium
has unique type of photosynthesis
not chlorophyll baseduses modified cell membrane (purple membrane)
contains bacteriorhodopsinabsorption of light by bacteriorhodopsin drives proton transport for ATP synthesis
halorhodopsin
Rhodopsin
Figure 20.13-The Photocycle of Bacteriorhodopsin
- chromophore + 7 membrane spanning domain-widely distributed among
procaryotes- found in marine bacterioplankton
- also found in cyanobacteria
- low O2 , high light intensity
As light driven proton pump isomerization
The ThermoplasmsThermoacidophiles (55-59°C; pH 1-2)
grow in refuse piles of coal minescell structure
lack cell wallsshape depends on temperature
59°C – irregular filamentat lower temperatures – spherical
may be flagellated and motilecell membrane strengthened by diglycerol tetraethers, lipopolysaccharides, and glycoproteinsnucleosome-like structures formed by association of DNA with histone like proteins
Figure 20.14
The ThermoplasmsExtremely Thermophilic S0-Metabolizers
Thermococcus and Pyrococcusmotile by flagellaoptimum growth temperatures 88 – 100°Cstrictly anaerobic; reduce sulfur to sulfide
Sulfate-reducing ArchaeaArchaeoglobuscell walls consist of glycoprotein subunitsoptimum 83°Cisolated from marine hydrothermal vents
Chapter 21Bacteria:
The Deinococci and Nonproteobacteria Gram
Negatives
Aquificae and Thermotogaeall thermophilicprocaryotes with optimum growth temperatures above 85°C belong to theArchaea
AquificaeThermotogae
Figure 21.1
Phylum Aquificae
the deepest (oldest) branch of BacteriaAquifex pyrophilus
gram-negative rodgrowth optimum of 85°C and maximum of 95°Cmicroaerophilicchemolithoautotroph
A. aeolicusgenome ~1/3 size of E. coli
Phylum Thermotogaesecond deepest branchbest studied Thermotoga
hyperthermophilesoptimum 80°C; maximum 90°C
grow in active geothermal areasmarine hydrothermal vents and terrestrial solfataric
springs
horizontal gene transfer~24% of coding sequences are similar to archaeal genes~16% similarity to Aquifex
Deinococcus-ThermusDeinococcus is best studied
spherical or rod-shapedin pairs or tetradsG(+)/ no typical G(+) cell wall
lacks teichoic acidlayered with outer membraneL-ornithine in peptidoglycan
plasma membrane has large amounts of palmitoleic acid
Deinococcus…Mesophilic and aerobicextraordinarily resistant to desiccation and radiation
Deinococcus radioduranscan survive 3-5 million rad (100 rad can be lethal to human)two circular chromosomes, a megaplasmid, a small plasmidNo novel DNA repair system?
has most efficient RecA and numerous repeatsdifferent chromosomal structureaccumulation of high level of Mn+2
DNA toroid
Photosynthetic Bacteria
three groups of gram-negative photosynthetic bacteria
Anoxygenic photosynthesisthe purple bacteriathe green bacteria
Oxygenic photosynthesisthe cyanobacteria
use water as an electron donor and generate oxygen during photosynthesis
differences in absorptionspectra correlateswith ecologicaldistribution
Figure 21.4
Phylum Cyanobacteriathe largest and most diverse group of photosynthesis bacteriaPhycobilisome
phycocyanin and phycoerythrin
Vary greatly in shape and appearance (Table 21.3)
Figure 21.7 (a)
Typical G(-) cell wall
Oxygenic Photosynthetic Bacteria
Figure 21.8
顫藻
- Unicellular rods or cocci
- Non-filamentous aggregates
-Filamentous
Motility of Cyanobacteria- lacking flagellaPhototaxis- use gas vacuoles to position in optimum illumination in water
Gliding motility (Box 21.1)- occurs on a solid surfaceVia cytoplasmic fibrils or filamentsMyxococcus xanthus (δ-proteobacteria)
type IV pili at the front pole pull cells forward S (social) motilityslime ejection at the rear pole to push the cells along the surface A (adventurous) motility
Swimming with unknown mechanismSynechococcus swim up to 25 μm/sec
Myxococcus xanthus has 2 motilitysystems for gliding
Current opinion in Microbiology (2007)10:1-6
A engine S engine
S motility
A motility
Ecology of Cyanobacteriatolerant of environmental extremes
thermophilic up to 75°Ccan cause blooms in nutrient-rich ponds and lakes
some produce toxinsoften form symbiotic relationships
Lichens: symbionts with protozoa and funginitrogen-fixing species with plants
An eutrophic pondFigure 21.11
Genus Chlamydianonmotile, coccoid, G(-) bacteria
cell walls lack muramic acid and peptidoglycan (however, they are pencillinsensitive)very small genomes (~ 1/3 of E. coli)
obligate intracellular parasitesextracellular elementary body (EB) intracellular reticulate body (RB; initial body) energy parasite
Figure 21.13b
Life cycle of Chlamydia
Important pathogens
C. trachomatis 砂眼causes trachoma, nongonococcal urethritis(花柳), and other diseases in humans
C. psittaci 鸚鵡熱causes psittacosis in humans and many other animals including parrots, turkeys, sheep, goat and cats
C. pneumoniaecommon cause of human pneumoniaassociated with atherosclerosis
Fig. 38.22
Phylum Spirochaetes
gram-negative bacteria slender, long with flexible helical shape
creeping (crawling) motility- axial filamentTreponema pallidium and syphilis 梅毒- metabolic crippled (lack TCA cycle …)Borrelia burgdorferi and Lyme disease
Figure 38.8 (b) and (c)
Lyme disease- localized stagedevelops 1 week to 10 days, expanding, ring-shaped, skin lesion, flu-like symptoms
disseminated stageoccurs weeks or months after infectionneurological abnormalities, heart inflammation, and arthritis
late stageoccurs years later, demyelination of neurons, behavioral changes, and symptoms resembling Alzheimer's disease and multiple sclerosis
Tick
Axial filament-
Figure 21.15 (a1) and (a2)
Figure 21.15 (b)
Complex of axial fibrils (periplasmic flagella)
current thought:axial fibrils rotate, causingcorkscrew-shaped outer sheathto rotate and move cell throughsurrounding liquid
Figure 21.16
Spirochete Motility