The Methylotrophic Bacteria
Three groups of microbes are considered here: the methane utilizers, the methanol utilizers, and the carbon monoxide utilizers. The methane utilizers (methanotrophs) appear to be composed of distinctive groups of bacteria with properties that set them apa
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The Methylotrophic Bacteria ROGER WHITTENBURY and HOWARD DALTON
Three groups of microbes are considered here: the methane utilizers, the methanol utilizers, and the carbon monoxide utilizers. The methane utilizers (methanotrophs) appear to be composed of distinctive groups of bacteria with properties that set them apart from the majority of other microbes. The methanol utilizers (methylotrophs-a term that also includes the methanotrophs) are a disparate group. While sharing certain metabolic pathways concerned with the utilizers of methanol and other C1 compounds, they can differ radically in other properties, e.g., some are prokaryotes and some eukaryotes. The carbon monoxide oxidizers are largely an unexplored group of microbes, and a generally accepted view of their biology has yet to be formulated.
Introduction to the Methanotrophs Methane-oxidizing bacteria have been recognized for many decades (Leadbetter and Foster, 1958), although attempts to isolate them have generally been unsuccessful. S6hngen isolated the first welldescribed organism in 1906 (Quayle, 1972) and named it Bacillus methanicus. This strain does not appear to have survived in any culture collection. However, it seems to be identical to Pseudomonas methanica, isolated by Dworkin and Foster (1956), and has proved to be the most commonly encountered species of methane-oxidizing bacteriumreflecting, probably, the enrichment methods used rather than its distribution and numbers in relation to other methane-oxidizing bacteria. Up to 1966, only three species had been isolated and described-Pseudomonas methanica, Methanomonas methanooxidans (Brown, Strawinski, and McCleskey, 1964), and M ethylococcus capsulatus (Foster and Davis, 1966). All three species were Gram-negative aerobes that used only methane and methanol as carbon and energy sources. Prior reports of both Gram-positive and Gram-negative methane oxidizers were too brief to evaluate (in many instances there were clear indications that such organisms were surviving by scavenging nutrients M. P. Starr et al. (eds.), The Prokaryotes © Springer-Verlag Berlin Heidelberg 1981
other than methane) or contained an element of ambiguity as to whether they were pure cultures. As none of these organisms appear to have survived or joined the pool of well-established methane-oxidizing bacteria, we have to assume that, up to 1966, only three distinct species had been shown to be authentic methane oxidizers. In 1970, Whittenbury and his colleagues (Whittenbury, Phillips, and Wilkinson, 1970) devised enrichment and isolation techniques that led to the establishment of many pure cultures of methane-oxidizing bacteria. Well over 100 strains were available and a basic scheme of classification was evolved (Davies and Whittenbury, 1970; Whittenbury, Davies, and Davey, 1970). Although species descriptions and taxonomic divisions have yet to be formally published, this scheme has served as a basis for later work. Since 1970, there have been many other reports of "new" species, especially by Russian workers. With
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