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SUMMARY: Growth of Methylococcus capsulatus on methane was inhibited by methanol (0.1%, v/v, and above), ethanol, n-propanol and n-butanol (0.01%, v/v, and above), but was unaffected by galactose, glucose, fructose, maltose, sucrose (at 0.1 M) or lactose (0.05 M). About one organism in 7 million grew well on solid medium using methanol vapour as a sole source of carbon and energy, but [14C]methanol was readily metabolized and assimilated by cultures growing on methane. Labelling patterns from [14C]methane and [14C]methanol were similar, indicating their assimilation by a common pathway. Dissimilarities between the labelling patterns obtained with 14CH4 and 14C-labelled formaldehyde, formate and carbonate indicated that the ribose phosphate cycle of formaldehyde assimilation may not account for all the carbon assimilated by M. capsulatus: significant incorporation of formate, carbon dioxide and possibly of intermediates of methane oxidation more reduced than formaldehyde may occur. 14C-Labelled ethanol and acetate showed restricted incorporation into lipid, leucine, glutamate, proline and arginine, indicating that M. capsulatus can produce acetyl coenzyme A from both compounds and introduce it into an incomplete biosynthetic tricarboxylic acid cycle. Methylococcus capsulatus was unable to assimilate more than trace amounts of [14C]glucose or sucrose.
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