Methylobacterium, a New Genus of Facultatively Methylotrophic Bacteria

Abstract

A new genus and a new species of methane-oxidizing bacteria are described. The colonies produced by these bacteria are pink, circular, and convex with entire margins. Cells are gram negative and are normally found singularly with some rosettes. Negative stains indicate polar flagellation. In thin sections, intracytoplasmic membranes, similar to those described as type II in other methylotrophs, were present when the cells were grown with methane. No such membranes were apparent when the cells were grown with the other carbon and energy sources tested. The serine pathway for formaldehyde incorporation is the pathway of C1 metabolism. The deoxyribonucleic acid base composition is 66 mol% guanine plus cytosine. Methylobacterium is proposed as the name for this new genus of rod-shaped, methane-oxidizing bacteria. The specific epithet in the name of the type species, Methylobacterium organophilum sp. nov., denotes the preference of this organism for organic carbon and energy sources more complex than methane. The type strain of M. organophilum is XX (= ATCC 27886). This bacterium differs from all previously described genera and species of methane-oxidizing bacteria in its ability to utilize a variety of organic substrates with carbon-carbon bonds as sources of carbon and energy. The pathways for methane oxidation and the assimilation of one-carbon units are repressed during growth on complex organic substrates.