“微生物学”考试时间地点

时间： 2000年 1月 9日上午 8:00-10:00

地点：四教 4206

Detailed phylogenetic tree of the Archaeabased on 16S ribosomal RNA sequenceComparisons

Archaeal Membranes and Cell Wall Archaea lack fatty acids, instead have hydrocarbon moieties b

onded to glycerol by ether (instead of ester) linkages Glycerol diethers and diglycerol tetraethers are the major clas

ses of lipids present in Archaea Archaea do not contain muramic acid and D-amino acids, as i

n Bacteria A pseudopeptidoglycan is found in some archaea, it consists of

two amino sugars: N-acetylglucosamine and N-acetyltalosaminuronic acid, with only L-amino acids linkages

Some contain a thick wall consists only polysaccharide Some contain cell walls made of glycoprotein Some lack carbohydrate in their cell walls and have walls cons

isting of only protein.

Chapter 20 Prokaryotic Diversity: Archaea

Extremely Halophilic ArchaeaMethane-Producing Archaea: MethanogenesHyperthermophilic ArchaeaThermoplasma: A Cell-Wall-Less ArchaeanLimits of Microbial Existence: TemperatureArchaea: Earliest Life Forms?

Extremely Halophilic Archaea:inhabitants of highly saline environments such as

solar salt evaporation ponds and natural salt lakes

Hypersaline habitats:Great Salt Lake in Utah

Seawater evaporating ponds: the red-purpleColor is due to bacterioruberins and bacterio-rhodopsin of halobacterium

Environments for extremely halophile

Solar salt evaporation pondsNatural salt lakesArtificial saline habitats (surfaces of heavily salte

d food such as certain fish and meats)Require at least 1.5 M (9%) NaCl for growthMost species require 2-4 M (12-23%) NaCl for gr

owthSome can grow at pH of 10-12No harmful to human and animals

Physiology of Extremely Halophilic Archaea

All are chemoorganotrophsMost are obligate aerobesAll require large amount of sodium for growthAll stain gram negatively, binary fission growthMost are nonmotileHalobacterium and Halococcus contain large plasmidsPeptidoglycan replaced by glycoportein in the cell wallCellular components exposed to the external environment r

equire high Na+ for stabilityCellular internal components require high K+ for stabilityNa+ stabilize the cell walls.

Bacteriorhodopsin and Light-mediated ATP Synthesis

Bacteriorhodopsin

Methane-Producing Archaea: MethanogensMethane formation occurs under strictly anoxic cond

itions.CO2-type substrates (CO2, HCOO- and CO) can be us

ed as carbon sources.Methyl substrates (CH3OH, CH3NH2+, (CH3)2NH+, (C

H3)3NH+, CH3SH, (CH3)2S) are methanogenic carbon sources.

Acetotrophic substrates such as acetate can also be used to produce methane. Three classes of methanogenic substrates are know

n and all release free energy suitable for ATP synthesis

Diversity and Physiology of Methanogenic Archaea

16S ribosomal RNA sequence analyses classify methanogen into seven major groups

All methanogens use NH4+ as a nitrogen source A few species can fix molecular nitrogen Nickel is a trace metal required by all methanog

ens, it is a component of coenzyme Factor430

Iron and Cobalt are also important for methanogens.

Pictures on the left: morphological diversity of methanogens

Diversity and Physiology of Methanogenic Archaea

Picture on the left are hyperthermophilic and thermophilic methanogens

Methanococcus jannaschii (85oC optimal)

Methanococcus igneus (88o

C optimal) Methanothermus fervidus (8

5oC optimal) Methanothrix thermophila 60oC optimal)

Picture on the right: thin section of methanogenic Archaea:Methanobrevibacter ruminantiumMethanosarcina barkeri

Unique Methanogenic Coenzymes Methanofuran (MF): a low-molecular-weight coenzyme tha

t interacts in the first step of methanogenesis from CO2. Methanopterin (reduced form tetrahydro-methanopterin o

r MF): a methanogenetic coenzyme containing a substituted pterin (蝶呤 ) ring, a C1 carrier during the reduction of CO2 to CH4.

Coenzyme M: involved in the final step in methane formation, is the carrier of the methyl group that is reduced to methane by the F430-methyl reductase enzyme complex in the final step of methanogenesis.

Coenzyme F430: a yellow, soluble, nickel-containing tetrapyrrole that plays an intimate role in the terminal step of methanogenesis as part of the methyl reductase system.

Unique Methanogenic CoenzymesCoenzymes involved in redox reactions

Coenzyme F420: an electron donor in methanogenesis.

7-mercaptoheptanoylthreonine phosphate (HS-HTP): an electron donor in methanogenesis, is the final unique coenzyme of the methanogens to be considered.

Coenzymes unique to methanogenic Archaea

Coenzymes Unique to Methanogenic Archaea

The oxidized form of F420 absorbs light at 420 nm and fluresces blue-green. On reduction, the coenzyme becomes colorless.

The fluorescence of F420 is a useful tool for preliminary identification of an organism as a methanogen

Autofluorescence of the methanogen Methanosarcina barkeri due to the presenceof the unique electron carrier F420.

Pathway of methanogenesis from CO2

Autotrophy in Methanogens

How autotrophic methanogens combine aspects of biosynthesis and bioenergetics. Note how half of the acetyl-CoA molecule prod

uced comes from reactions leading to methanogenesis.

C1-carrying corrinoid-containing enzyme

Methanogenesis from methyl compounds and acetate

Utilization of reactions of the acetyl-CoA pathwayduring growth on methanol (a) acetate (b)

Energetic of MethanogenesisATP synthesis linked to a proton

motive force established during theterminal step of methanogenesis

Hyperthermophilic ArchaeaTemperature Optima above 80oC

Most isolated from geothermally heated soils or waters containing sulfur an sulfides

Most are obligate anaerobes Many grow chemolithotrophically, wit

h H2 as energy source

Hyperthermophilic from Volcanic Habitats Acidophilic Hyperthermophilic Archaea

Sulfolobus acidocaldarius

Acidianus infernus

The first such organism discovered, Sulfolobus, grows in sulfur-richhot acid springs at temperature up to 90oC and at pH values of 1-5.Acidianus, a facultative aerobe resembling Sulfolobus is also presentin acidic solfataric springs, it can also grow anaerobically.

Hyperthermophilic from Volcanic Habitats Acidophilic Hyperthermophilic Archaea

Spherical, obligately anaerobic, S0-respiring organism.

Grows best at neutral pH and 80-90oC

Desulfurococcus saccharovorans

Hyperthermophilic from Volcanic Habitats Acidophilic Hyperthermophilic Archaea

Thermoproteus and Thermofilum inhabit neutral or slightly acidic hot springs, are highly variable in length, ranging from 1-80 microns.

Both are strict anaerobes that carry out a S0-based anaerobic respiration. Most can grow chemolithotrophically.

Thermoproteus neutrophilus

Thermofilum librum

Thermofilum librum

Hyperthermophilic from Submarine Volcanic Areas

Boiling points increase with water depth. Pyrodium has a growth optimum of 105oC, has higher GC(62%). Cells are irregularly disc- and dish-shaped, grow in culture as a mo

ldlike layer on sulfur crystals suspended in the medium. Strict anaerobe that grows chemolithotrophically at neutral pH on

H2 with S0 as electron acceptor. Growth occur between 82-110oC.

Pyrodium occultum (optima 105oC)

Hyperthermophilic from Submarine Volcanic Areas

Pyrobaculum is capable of both aerobic respiration and denitrification (NO3- N2).

Organic or inorganic substrates can be used as electron donors Maxima T=103oC H2, as well as various complex nutrients but not sugars support its gro

wth. Elemental So is not used by this organism, even inhibits its growth.

Pyrobaculum aerophilum (optima 100oC)

Hyperthermophilic from Submarine Volcanic Areas

Thermococcus, a spherical hyperthermophilic archaean indigenous to anoxic submarine thermal waters in various location worldwide.

Contains a tuft of polar flagella, highly motile. Obligately anaerobic chemoorganotroph that grows on proteins and oth

er complex organic mixtures (including some sugars) with

Hyperthermococcus celer Dividing cells of Pyrococcus furiosus

S0 as electron acceptor.

Optima T=88oC

Pyrococcus grows at between 70-106oC with an optimum of 100 oC.Metabolic requirement similar to Hyperthermococcus.

Hyperthermophilic from Submarine Volcanic Areas

Staphylothermus consists of spherical cells about 1 micron in diameter that form aggregates of up to 100 cells.

Strictly anaerobic hyperthermophile growing optimally at 92oC. Capable of growth between 65 and 98oC. S0 is required for growth, yet oxidation of complex organic compou

nds is not tightly coupled to S0 reduction.

Staphylothermus marinus

Hyperthermophilic from Submarine Volcanic Areas

Most Archaea use S0 as an electron acceptor for anoxic growth, most are unable to use sulfate as an electron acceptor.

Archaeoglobus, is a true sulfate-reducing hyper-thermophile.

Grow at between 64 and 92oC with T optima=83oC Share some metabolic features with methanogens.

Archaeoglobus lithotrophicus

Methanopyrus kandleri Methanopyrus: gram-positiverod-shaped methanogen grownabove 100oC.The most ancient hyper-thermophileShare phenotypical propertieswith both the hyperthermophilesand methanogens.

Hyperthermophilic from Submarine Volcanic Areas

Aquifex and Thermotoga are not Archaea but hyperthermophilic bacteria that otherwise strongly resemble hyperthermophilic Archaea.

Thermotoga maritima (80oC)

Aquifex pyrophilus (85oC)

Chemoorganotrophic and anaerobic

Obligate chemolithotrophic, micro-aerobically or anaerobically growthwith only H2, S0 or S2O3- as electron donor and O2 or NO3- as electronacceptor.

Thermoplasma: A Cell-Wall-Less Archaea

Thermoplasma acidophilum is a cell-wall-less prokaryote resembling the mycoplasmas.

Acidophilic, aerobic chemoorganotroph, thermophilic Archaea (pH=2 and To=55oC).

All strains of Thermoplasma have been isolated from self-heating coal refuse piles.

Thermoplasma acidophiluman acidophilic, thermophilicmycoplasma-like archaea

Thermoplasma volcaniumshadowed preparation

Thermoplasma volcanium has been isolatedfrom Solfatara fields throughout the world.

Thermoplasma: A Cell-Wall -Less Archaea

Thermoplasma has evolved a cell membrane of chemically unique structure.

It contains lipopolysaccharide consisting of a tetraether lipid with mannose and glucose units. Self-heating coal refuse pile

habitat of ThermoplasmaThe membrane also contains glyco-proteins but not sterol, the overallstructure render the thermoplasmamembrane stable to hot acid conditions

Limits of Microbial Existence: Temperature

Laboratory experiments on the heat stability of biomolecules suggest that living processes could be maintained at temperature as high as 140-150oC.

Structure of the tetraether lipoglycan of Thermoplasma acidophilum

Pyrodictium occultum (optima 105oC, maxima 110oC)

Archaea: Earliest Life Forms?Early geochemical conditions:

High temperature High salt Low pH Strict anoxic conditions

Only Archaea can stand such environmental extrems.

Do you agree with the argument: Archaea are the Earliest Life Forms