In discussing the Archaea earlier, we encountered species capable of the production of methane, a gas found widely in such diverse locations as marshes, sewage sludge and animal intestines. Certain proteobac-teria are able to utilise this methane as a carbon and energy source and are known as methanotrophs.
Methanotrophs are strict aerobes, requiring oxy-gen for the oxidation of methane. The methane-generating bacteria, however, as weâ€™ve seen are anaer-obes; methanotrophs are consequently to be found at aerobic/anaerobic interfaces such as topsoil, where they
can find both the oxygen and the methane they require. The methane is firstly oxidised to methanol, then to formaldehyde, by means of separate enzyme systems. Some of the carbon in formaldehyde is assimilated into organic cellular material, while some is further oxidised to carbon dioxide.
Bacteria able to utilise other single-carbon com-pounds such as methanol (CH3OH) or methylamine (CH3NH2) are termed methylotrophs. Depending on whether they possess the enzyme methane monooxyge-nase (MMO), they may also be methanotrophs.
Representative genera: Methylomonas, Methylococcus