PHYSIOLOGY OF THE ALKALIPHILIC METHANOGEN Z-7936, A NEW STRAIN OF METHANOSALSUS-ZHILINAEAE ISOLATED FROM LAKE MAGADI

A new obligately alkaliphilic, methylotrophic methanogen 2-7936 was is olated from the soda lake Magadi (Kenya). According to its phenotypic and genotypic properties, the isolate belonged to Methanosalsus (Metha nohalopltilus) zhilinaeae; it exhibited a 91% homology with the type s train of this formerly monotypic species. The only growth substrates w ere methanol; mono-, di-, and trimethylamine; and dimethyl sulfide. Me thylamine and ammonium at concentrations above 30 mM inhibited growth. Methanogenesis on methanol was partially inhibited by methylated amin es and completely inhibited by 1 atm hydrogen. Strain 2-7936 did not r equire Cl- but was obligately dependent on Na+ and HCO3-. It was oblig ately alkaliphilic and grew within a pH range of 8-10. The pH optima f or methanogenesis on methanol and trimethylamine were different (9-9.5 and 8.5, respectively). The phenotypic similarity and phylogenetic di stinctions between the groups of halophilic and alkaliphilic methylotr ophic methanogens indicate their independent origin and the identical function performed by them in anaerobic microbial communities.