Methane fermentation of formate by Methanobacillus omelianskii.

The pathway of the methane fermentation of formate was investigated in several organisms by Stephenson and Stickland (1933), Barker (1941) and Stadtman and Barker (1951). Since in several instances H2 and C02 were generated during fermentation, the decomposition of formate would probably involve some prior oxidation to C02 and subsequent reduction to CH4 by the C02-reduction scheme of Van Niel and Barker (Barker, 1956). However, the alternate possibility of a direct reduction of formate was never investigated satisfactorily. Stadtman and Barker (1951) found C14 impractical as a tracer for a possible reductive pathway with Methanococcus vannielii because of the vigorous isotopic exchange between formate and C02. In this study, with deuterium as a tracer an(d hypophosphite as a selective inhibitor of formic dehydrogenase, both oxidative and reductive incorporations of formate into methane are clearly demonstrable with Methanobacillus omelianskii (Barker, 1956) previously refered to as Methanobacterium omelianskii. Normally the organism couples the reduction of C02 to CH4 with the oxidation of alcohols to acids or ketones. Unlike typical formate fermenters, it does not metabolize formate rapidly enough to use it as a CO2 substitute for growth (Barker, 1941).