In vivo studies of primary alcohols, aldehydes and carboxylic acids as electron donors for the methane mono-oxygenase in a variety of methanotrophs

C₂ to C₄ primary alcohols and their corresponding aldehydes were oxidized by type I, type II and type X obligate methanotrophs. Reducing equivalents from each oxidation step could be utilized, in vivo, to stimulate methane mono-oxygenase activity. As neither oxidation step produces NADH directly, these observations are presented as evidence for reverse electron transport in methanotrophs. In type II methanotrophs, 5 mM-acetate, propionate and butyrate also stimulate methane mono-oxygenase activity apparently by inducing the breakdown of poly-β-hydroxybutyrate, subsequent metabolism of β-hydroxybutyrate giving rise to NADH.