Transcript Thermoplasma: A Cell-Wall

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 时间：2000年1月9日上午8:00-10:00
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Detailed phylogenetic tree of the Archaea
based on 16S ribosomal RNA sequence
Comparisons
Archaeal Membranes and Cell Wall
 Archaea lack fatty acids, instead have hydrocarbon moieties
bonded to glycerol by ether (instead of ester) linkages
 Glycerol diethers and diglycerol tetraethers are the major
classes of lipids present in Archaea
 Archaea do not contain muramic acid and D-amino acids, as
in Bacteria
 A pseudopeptidoglycan is found in some archaea, it consists of
two amino sugars: N-acetylglucosamine and Nacetyltalosaminuronic 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
consisting of only protein.
Chapter 20
Prokaryotic Diversity: Archaea
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Extremely Halophilic Archaea
Methane-Producing Archaea: Methanogenes
Hyperthermophilic Archaea
Thermoplasma: A Cell-Wall-Less Archaean
Limits of Microbial Existence: Temperature
Archaea: Earliest Life Forms?
Extremely Halophilic Archaea:
inhabitants of highly saline environments such as
solar salt evaporation ponds and natural salt lakes
Hypersaline habitats: Seawater evaporating ponds: the red-purple
Great Salt Lake in Utah Color is due to bacterioruberins and bacteriorhodopsin of halobacterium
Environments for extremely halophile
 Solar salt evaporation ponds
 Natural salt lakes
 Artificial saline habitats (surfaces of heavily
salted food such as certain fish and meats)
 Require at least 1.5 M (9%) NaCl for growth
 Most species require 2-4 M (12-23%) NaCl for
growth
 Some can grow at pH of 10-12
 No harmful to human and animals
Physiology of Extremely Halophilic Archaea
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All are chemoorganotrophs
Most are obligate aerobes
All require large amount of sodium for growth
All stain gram negatively, binary fission growth
Most are nonmotile
Halobacterium and Halococcus contain large plasmids
Peptidoglycan replaced by glycoportein in the cell wall
Cellular components exposed to the external
environment require high Na+ for stability
 Cellular internal components require high K+ for
stability
 Na+ stabilize the cell walls.
Bacteriorhodopsin and Light-mediated ATP Synthesis
Bacteriorhodopsin
Methane-Producing Archaea: Methanogens
 Methane formation occurs under strictly anoxic
conditions.
 CO2-type substrates (CO2, HCOO- and CO) can be
used as carbon sources.
 Methyl substrates (CH3OH, CH3NH2+, (CH3)2NH+,
(CH3)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
known 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
methanogens, 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
(88oC optimal)
 Methanothermus fervidus
(85oC optimal)
 Methanothrix thermophila
 60oC optimal)
Picture on the right: thin section of methanogenic Archaea:
Methanobrevibacter ruminantium
Methanosarcina barkeri
Unique Methanogenic Coenzymes
 Methanofuran (MF): a low-molecular-weight coenzyme
that interacts in the first step of methanogenesis from CO2.
 Methanopterin (reduced form tetrahydro-methanopterin or
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 Coenzymes
Coenzymes involved in redox reactions
 Coenzyme F420: an electron donor in
methanogenesis.
 7-mercaptoheptanoylthreonine phosphate (HSHTP): 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 presence
of the unique electron carrier F420.
Pathway of methanogenesis from CO2
Autotrophy in Methanogens
C1-carrying corrinoidcontaining enzyme
How autotrophic methanogens combine aspects of biosynthesis
and bioenergetics. Note how half of the acetyl-CoA molecule
produced comes from reactions leading to methanogenesis.
Methanogenesis from methyl compounds and acetate
Utilization of reactions of the acetyl-CoA pathway
during growth on methanol (a) acetate (b)
Energetic of Methanogenesis
ATP synthesis linked to a proton
motive force established during the
terminal step of methanogenesis
Hyperthermophilic Archaea
Temperature Optima above 80oC
 Most isolated from geothermally
heated soils or waters containing
sulfur an sulfides
 Most are obligate anaerobes
 Many grow chemolithotrophically,
with H2 as energy source
Hyperthermophilic from Volcanic Habitats
Acidophilic Hyperthermophilic Archaea
The first such organism discovered, Sulfolobus, grows in sulfur-rich
hot acid springs at temperature up to 90oC and at pH values of 1-5.
Acidianus, a facultative aerobe resembling Sulfolobus is also present
in acidic solfataric springs, it can also grow anaerobically.
Acidianus infernus
Sulfolobus acidocaldarius
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
moldlike 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
(NO3N2).
 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
growth.
 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 other complex organic mixtures (including some sugars) with
Hyperthermococcus celer Dividing cells of
S0 as electron acceptor.
Pyrococcus furiosus Optima T=88oC
Pyrococcus grows at between 70106oC 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
compounds 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 hyperthermophile.
 Grow at between 64 and 92oC with T optima=83oC
 Share some metabolic features with methanogens.
Methanopyrus kandleri
Archaeoglobus lithotrophicus
Methanopyrus: gram-positive
rod-shaped methanogen grown
above 100oC.
The most ancient hyperthermophile
Share phenotypical properties
with both the hyperthermophiles
and methanogens.
Hyperthermophilic from Submarine Volcanic Areas
 Aquifex and Thermotoga are not Archaea but
hyperthermophilic bacteria that otherwise strongly
resemble hyperthermophilic Archaea.
Thermotoga maritima (80oC)
Chemoorganotrophic and anaerobic
Aquifex pyrophilus (85oC)
Obligate chemolithotrophic, microaerobically or anaerobically growth
with only H2, S0 or S2O3- as electron
donor and O2 or NO3- as electron
acceptor.
Thermoplasma: A Cell-Wall-Less Archaea
Thermoplasma acidophilum
an acidophilic, thermophilic
mycoplasma-like archaea
Thermoplasma volcanium has been isolated
from Solfatara fields throughout the world.
Thermoplasma volcanium
shadowed preparation
 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: A Cell-Wall
-Less Archaea
Self-heating coal refuse pile
habitat of Thermoplasma
 Thermoplasma has evolved a
cell membrane of chemically
unique structure.
 It contains lipopolysaccharide
consisting of a tetraether lipid
with mannose and glucose units.
The membrane also contains glycoproteins but not sterol, the overall
structure render the thermoplasma
membrane stable to hot acid
conditions
Limits of Microbial Existence: Temperature
Pyrodictium occultum (optima 105oC, maxima 110oC)
 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
Archaea: Earliest Life Forms?
 Early geochemical conditions:
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High temperature
High salt
Low pH
Strict anoxic conditions
 Only Archaea can stand such environmental
extrems.
 Do you agree with the argument:
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Archaea are the Earliest Life Forms