Archaebacteria 12847268357901 Phpapp01
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Transcript of Archaebacteria 12847268357901 Phpapp01
ARCHAEBACTERIA
CONTENTS
• Introduction• Archaeal cell walls• Archaeal lipids & membranes• Genetics & molecular biology• Metabolism• Archaeal taxonomy• Significance of Archaebacteria• References
Introduction
Introduction to the ArchaeaMorphology
•Stain either Gram +ve or Gram –ve
•Shapes – Spherical, rod, spiral, lobed, irregularly shaped or pleomorphic
•Single cells or filaments or aggregates, diameter from 0.1 to over 15 μm
•Multiplication – binary fission, budding, fragmentation or other mechanisms
Contd…Contd…
• Physiology•Aerobic, facultative and strictly
anaerobic
•Range from chemolithotrophs to organotrophs
•Mesophilic & hyperthermophiles
•Found in extreme environments
•Few are symbionts in animal digestive system
Contd…Contd…
Archaeal cell walls
Structure
Gram +ve Archaea•Single thick homogenous layer as in
Gram +ve bacteria
Gram +ve Archaea• lack outer membrane & complex
peptidoglycan network•have a surface layer of proteins or
glycoproteins
Contd…Contd…
Chemistry
Gram +ve Archaea•Variety of complex polymers
•Methanobacterium – pseudomurein
•Methanosarcina & Halococcus – complex polysaccharides similar to chondroitin sulphate of animal connective tissue
•Other heteropolysaccharides are also found Contd…Contd…
Gram -ve Archaea•Layer of protein or glycoprotein outside
their PM (20 to 40 nm thick)
•Methanolobus, Halobacterium & several extreme thermophiles (Sulfolobus, Thermoproteus & Pyrodictium) consist of glycoprotein units
•Methanococcus, Metahnomicrobium, Methanogenium & Desulfurococcus consist of protein units
Contd…Contd…
Archaeal Lipids & Membranes
•Branched chain hydrocarbon attached to glycerol by ether links rather than fatty acids joined by ester links
•Sometimes two glycerol groups – form an extremely long tetraether (40C)
•Length is adjusted by cyclizing the chain to form pentacyclic rings
•Polar lipids like phospholipids, sulfolipids & glycolipids are present
•7 to 30% are non polar lipidsContd…Contd…
• lipids can be combined in various ways – membranes of different rigidity
– C20 diethers – regular bilayer membrane– C40 tetraether – much more rigid
monolayer membrane
Contd…Contd…
Genetics & Molecular Biology
•Circular DNA – like bacteria
•Genomes are significantly smaller than bacteria.
– E. coli – 2.5 x 109 Daltons– T. acidophilum – 0.8 x 109 Daltons
•G + C content varies from 21 - 68 mol %
•mRNA – similar to bacterial mRNA
•TψC arm of tRNA – pseudouridine / 1-methyl pseudouridine
Contd…Contd…
•Sensitive to anisomycin & insensitive to chloramphenicol & kanamycin
•EF-2 reacts with diphtheria toxin
•Many methanogens - nucleosomes
•DNA dependent polymerases resemble eukaryotic enzymes rather than prokaryotic polymerases
Contd…Contd…
Metabolism
•CH metabolism is best understood
•6- phosphofructokinase is absent & E-M p/w is not followed
•Extreme halophiles & thermophiles – modified form of E-D p/w wherein initial intermediates are not phosphorylated
•Methanogens do not catabolise glucose
•Gluconeogenesis – reversal of E-M p/w
•All oxidize pyruvate – acetyl coA using pyruvate oxidoreductase
Contd…Contd…
•Biosynthetic p/w – similar to those in other organisms
» Some methanogens can fix atmospheric N2
» Few employ glycogen as the main reserve material
•Autotrophy is widespread among methanogens & extreme thermophiles
•Thermoproteus & Sulfolobus – fix CO2 by reductive TCA cycle
•Methanogens & extreme thermophiles –fix CO2 by reductive acetyl coA p/wContd…Contd…
Reductive TCA cycle
Contd…Contd…
Archaeal Taxonomy
Phylum Crenarchaeota•Most are extremely thermophilic &
many are acidophiles and S dependent
•S – as electron acceptor or electron source by lithotrophs
•Almost all are strict anaerobes & grow in geothermally heated water / soils that contain elemental sulfur
Contd…Contd…
•Divided into one class – Thermoprotrei & three orders :
» Thermoproteales» Sulfolobales» Desulfurococcales
•Contain 69 genera – two of the better studied genera are Thermoproteus & Sulfolobus
Contd…Contd…
Sulfolobus
• Gram –ve, aerobic, irregularly lobed spherical archaeons
• Optimum temp.– 70 to 80 0C & optimum pH 2 - 3hence also referred to as thermoacidophiles
• Cell wall – lipoprotein & CH, lacks peptidoglycan
• Grow lithotrophically on S granules in hot S springs oxidizing S to Sulfuric acid
• Oxygen Is the normal electron acceptor, Fe+3
may be usedContd…Contd…
• Sugars & amino acids (glutamate) also serve as C & energy sources
Contd…Contd…
Thermoproteus
• Gram –ve, strictly anaerobic, hyperthermophilic long thin rod, can be bent or branched
• Cell wall consists of glycoprotein
• Grows at temp. from 70 - 97 0C & pH 2.5 – 6.5
• Found in hot springs & other hot aquatic habitats rich in sulfur
• Can grow organotrophically & oxidize glucose, amino acids, alcohols & organic acids with S as TEA Contd…Contd…
An aquatic spring in Japan with Thermoproteus growth
• Grows chemolithtrophically using Hydrogen & S0
• CO & CO2 can serve as the sole C source
Thermoproteus
Contd…Contd…
Phylum Euryarchaeota
• Very diverse with 7 classes viz. Methanococcus, Methanobacteria, Halobacteria, Thermoplasmata, Thermococci, Archaeglobi & Methanopyri
• Consists of 9 orders & 15 families
• Includes methanogens, extreme halophiles, sulphate reducers & many extreme thermophiles with S dependent metabolism
Contd…Contd…
The Methanogens• Strict anaerobes that obtain energy by
converting CO2, H2, formate, methanol, acetate & other compounds to either CH4 or CH4 & CO2
• Autotrophic when growing on CO2 & H2
• 5 orders (Methanobacteriales, Methanococcales, Methanomicrobiales, Methanosarcinales & Methanopyrales) & 26 genera
• Metabolism is unusual• Unique cofactors like H4MPT, MFR, Coenzyme M
Coenzyme F420, Coenzyme F430
• Coenzyme F420 carries electrons and Hydrogen• Coenzyme F430 cofactor for methyl co-M methyl
reductase
Contd…Contd…
Methane synthesis from CO2 by Methanobacterium thermoautotrophicum
Contd…Contd…
• Some live autotrophically – acetyl coA from two molecules of CO2 & then converting acetyl coA to pyruvate & other products
• Found in anaerobic environment rich in organic matter
• Rumen & intestine of animals, fresh water & marine sediments, swamps & marshes, hot springs, anaerobic sludge digesters & anaerobic protozoa
• Ecological significance• Cow belches 200 – 400 ltrs CH4/day
• Source of energy for sewage treatment plantsContd…Contd…
E.g. Halobacterium salinarium
• Unusual type of photosynthesis
• On exposure to sunlight – purple membrane – bacteriorhodopsin
• Four types of rhodopsins• Bacteriorhodopsin – proton transport for ATP
synthesis• Halorhodopsin – uses light energy to transport
chloride ions into the cell & maintains KCl conc.
• Remaining two – photoreceptors, one for red light & one for blue
Contd…Contd…
• Ecological hazards• Methane gas – Greenhouse gas• Can oxidize Fe0
• May contribute to corrosion of buried or submerged iron pipes
Yellowstone National Park
M. thermoautotrophicum
Contd…Contd…
The Halobacteria• Class Halobacteria – 15 genera in one family,
the Halobacteriaceae
• Aerobic chemoheterotrophs with respiratory metabolism
• Non motile or motile by lophotrichous flagella
• Absolutely dependent on high NaCl conc.• At least 1.5 M NaCl, growth optimum at 3 – 4
M • Cell wall disintegrates below 1.5 M conc.• Grow only in high salinity habitats• Cause spoilage of salted fish Contd…Contd…
Purple lake in AustraliaH. salinarium
Contd…Contd…
The Thermoplasms
• Class Thermoplasmata
• Thermoacidophiles that lack cell wall
• Two genera, Thermoplasma & Pichrophilus
• Thermoplasma• Grows in refuse piles of coal mines• Temperatures from 55 – 590C & pH 1-2• Plasma membrane is strengthened by large
quantities of diglycerol, tetraethers, lipopolysaccharides & glycolipids
• DNA stabilized by nucleosomesContd…Contd…
• At 590C - irregularly shaped & at lower temperatures – spherical
• May be motile by flagella
Contd…Contd…
• Picrophilus• Lacks cell wall , has S layer outside PM• Aerobic, irregularly shaped cocci, 1 – 1.5 μm
in diameter• Temp. range 47 – 650C, optimum temp. 600C• pH below 3.5, optimum pH 0.7• Can grow at pH 0
Contd…Contd…
Extremely Thermophilic S0 Metabolizers
• Class Thermococci, order Thermococcales
• Strictly anaerobic
• Reduce sulfur to sulfide
• Motile by flagella
• Optimum growth temp. 88 –1000C
• Two genera, Thermococcus & PyrococcusContd…Contd…
Sulfate Reducing Archaea
• Class Archaeglobi, order Archaeoglobales
• Gram –ve, irregular coccoid cells
• Cell wall – glycoprotein subunits
• Electron sources – hydrogen, lactate & glucose, reduce sulfate, sulfite or thiosulfate to sulfide
• S is not used as electron acceptor
• Extremely thermophilic, optimum temp. around 830C, occur in hydrothermal vents
Contd…Contd…
Significance of Archaea
• Methanogens are used for the production of methane which is a rich source of energy
• Preparation of glycoproteins & proteins from archaeal cultures are used to increase body’s defense against infection
• Halophilic archaea are used to prescreen antitumor drugs active on eukaryotic proteins
• Thermophilic archaea are used in PCR
References
• Prescott, Lansing M.; Harley, John P. and Klein, Donald A.,2003. Microbiology, 5th edition. McGraw – Hill
• www.euarch.blogspot.com• www.filebox.vt.edu• www.nature.com/ntmicro/journal/v5/n4• www.fib_tab/nrmicro1619_F3.html• www.microbewiki.kenyon.edu/