Archaebacteria
- 2. CONTENTS Introduction Archaeal cell walls Archaeal lipids & membranes Genetics & molecular biology Metabolism Archaeal taxonomy Significance of Archaebacteria References
- 3. Introduction
- 4. Introduction to the Archaea Morphology 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 μ m Multiplication – binary fission, budding, fragmentation or other mechanisms Contd…
- 5. 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…
- 7. 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…
- 8. 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…
- 9. 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…
- 10. Archaeal Lipids & Membranes
- 11. 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 lipids Contd…
- 12. lipids can be combined in various ways – membranes of different rigidity C20 diethers – regular bilayer membrane C40 tetraether – much more rigid monolayer membrane Contd…
- 13. Genetics & Molecular Biology
- 14. Circular DNA – like bacteria Genomes are significantly smaller than bacteria. E. coli – 2.5 x 10 9 Daltons T. acidophilum – 0.8 x 10 9 Daltons G + C content varies from 21 - 68 mol % mRNA – similar to bacterial mRNA T ψ C arm of tRNA – pseudouridine / 1-methyl pseudouridine Contd…
- 15. 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…
- 16. Metabolism
- 17. 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…
- 18. Biosynthetic p/w – similar to those in other organisms Some methanogens can fix atmospheric N 2 Few employ glycogen as the main reserve material Autotrophy is widespread among methanogens & extreme thermophiles Thermoproteus & Sulfolobus – fix CO 2 by reductive TCA cycle Methanogens & extreme thermophiles –fix CO 2 by reductive acetyl coA p/w Contd…
- 19. Reductive TCA cycle Contd…
- 21. 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…
- 22. Divided into one class – Thermoprotrei & three orders : Thermoproteales Sulfolobales Desulfurococcales Contain 69 genera – two of the better studied genera are Thermoproteus & Sulfolobus Contd…
- 23. Sulfolobus Gram –ve, aerobic, irregularly lobed spherical archaeons Optimum temp.– 70 to 80 0 C & optimum pH 2 - 3 hence 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 used Contd…
- 24. Sugars & amino acids (glutamate) also serve as C & energy sources Contd…
- 25. 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 0 C & 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…
- 26. An aquatic spring in Japan with Thermoproteus growth Grows chemolithtrophically using Hydrogen & S 0 CO & CO 2 can serve as the sole C source Thermoproteus Contd…
- 27. 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…
- 28. The Methanogens Strict anaerobes that obtain energy by converting CO 2 , H 2 , formate, methanol, acetate & other compounds to either CH 4 or CH 4 & CO 2 Autotrophic when growing on CO 2 & H 2 5 orders ( Methanobacteriales, Methanococcales, Methanomicrobiales, Methanosarcinales & Methanopyrales) & 26 genera Metabolism is unusual Unique cofactors like H 4 MPT, MFR, Coenzyme M Coenzyme F 420 , Coenzyme F 430 Coenzyme F 420 carries electrons and Hydrogen Coenzyme F 430 cofactor for methyl co-M methyl reductase Contd…
- 29. Methane synthesis from CO 2 by Methanobacterium thermoautotrophicum Contd…
- 30. Some live autotrophically – acetyl coA from two molecules of CO 2 & 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 CH 4 /day Source of energy for sewage treatment plants Contd…
- 31. 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…
- 32. Ecological hazards Methane gas – Greenhouse gas Can oxidize Fe 0 May contribute to corrosion of buried or submerged iron pipes Yellowstone National Park M. thermoautotrophicum Contd…
- 33. 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…
- 34. Purple lake in Australia H. salinarium Contd…
- 35. The Thermoplasms Class Thermoplasmata Thermoacidophiles that lack cell wall Two genera, Thermoplasma & Pichrophilus Thermoplasma Grows in refuse piles of coal mines Temperatures from 55 – 59 0 C & pH 1-2 Plasma membrane is strengthened by large quantities of diglycerol, tetraethers, lipopolysaccharides & glycolipids DNA stabilized by nucleosomes Contd…
- 36. At 59 0 C - irregularly shaped & at lower temperatures – spherical May be motile by flagella Contd…
- 37. Picrophilus Lacks cell wall , has S layer outside PM Aerobic, irregularly shaped cocci, 1 – 1.5 μ m in diameter Temp. range 47 – 65 0 C, optimum temp. 60 0 C pH below 3.5, optimum pH 0.7 Can grow at pH 0 Contd…
- 38. Extremely Thermophilic S 0 Metabolizers Class Thermococci, order Thermococcales Strictly anaerobic Reduce sulfur to sulfide Motile by flagella Optimum growth temp. 88 –100 0 C Two genera, Thermococcus & Pyrococcus Contd…
- 39. 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 83 0 C, occur in hydrothermal vents Contd…
- 41. 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
- 42. References Prescott, Lansing M.; Harley, John P. and Klein, Donald A.,2003. Microbiology, 5 th 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/