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“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
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