title: Methanobacterium thermoautotrophicus sp. n., an anaerobic, autotrophic, extreme thermophile.
abstract: The isolation of a new methanogenic bacterium, Methanobacterium thermoautotrophicus sp. n., is described. Successful isolation required a medium containing inorganic salts, an atmosphere consisting of an 80:20 mixture of hydrogen-carbon dioxide, and incubation temperatures of 65 to 70 C. Isolates of M. thermoautotrophicus were gram-positive, nonmotile, irregularly curved rods which frequently formed long filaments. The organism was found to be an autotroph and a strict anaerobe, and to have a pH optimum of 7.2 to 7.6. The optimal temperature for growth was 65 to 70 C, the maximum being 75 C and the minimum about 40 C. The generation time at the optimum was about 5 hr. The deoxyribonucleic acid of M. thermoautotrophicus had a guanine plus cytosine (GC) content of 52 moles per cent, whereas Methanobacterium sp. strain M.O.H. had a GC content of 38%. When heated, intact ribosomes of Methanobacterium sp. strain M.O.H. were stable up to 55 C and had a T(m) of 73 C. In contrast, ribosomes of M. thermoautotrophicus were stable up to 75 C and had a T(m) of 82 C. Upon complete thermal denaturation, ribosomes of strain M.O.H. underwent a 59% hyperchromic shift, whereas those of the thermophile showed only a 20% increase in hyperchromicity. Methane formation in cell-free extracts of M. thermoautotrophicus was temperature-dependent and required hydrogen and carbon dioxide; methyl cobalamin served as a methyl donor, and addition of coenzyme M stimulated methanogenesis.
mesh_terms: D000693:Anaerobiosis; D001419:Bacteria / Q000032:analysis / Q000145:classification* / Q000166:cytology / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism; D002245:Carbon Dioxide; D002474:Cell-Free System; D002499:Centrifugation, Density Gradient; D002586:Cesium; D002712:Chlorides; D002849:Chromatography, Gas; D003067:Coenzymes; D003470:Culture Media; D003596:Cytosine / Q000032:analysis; D004269:DNA, Bacterial / Q000032:analysis; D003720:Densitometry; D006147:Guanine / Q000032:analysis; D006358:Hot Temperature; D006859:Hydrogen; D006863:Hydrogen-Ion Concentration; D008697:Methane / Q000096:biosynthesis*; D008858:Microscopy, Phase-Contrast; D012270:Ribosomes; D012722:Sewage; D014805:Vitamin B 12; D014871:Water Microbiology
chemical_list: D002712:Chlorides; D003067:Coenzymes; D003470:Culture Media; D004269:DNA, Bacterial; D012722:Sewage; D002245:Carbon Dioxide; D002586:Cesium; D006147:Guanine; D006859:Hydrogen; D003596:Cytosine; D008697:Methane; D014805:Vitamin B 12