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