[Ability of obligate methylotrophs to perform nitrogen fixation]

The ability for nitrification was studied among mesophilic and thermophilic cultures of obligate methylotrophs Methylobacter ucrainicus, Methylomonas methanica, and Methylococcus thermophilus. The strains were almost incapable of nitrification under autotrophic conditions. In the presence of methane, however, they oxidized NH+4 TO NO-2: over 150 mg/litre NO-2 nitrogen was found in the cultural broth. Therefore, obligate methylotrophs are capable of heterotrophic nitrification. The level of nitrification suggests that it is not a side reaction but a necessary stage of the metabolism of obligate methylotrophs. The phenotype relation between obligate methylotrophs and nitrifying organisms is discussed.