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Abstract:
Termites, cockroaches, and scarab beetles are the only insects known that emit methane, but they do so in impressive amounts. Methanogenesis occurs in the enlarged hindgut compartment and is fueled by hydrogen and reduced one-carbon compounds that are formed during the fermentative breakdown of plant fiber and humus. The methanogens typically colonize intestinal surfaces or occur as endosymbionts of protists. They fall into three major phylogenetic groups (Methanobacteriales, Methanosarcinales, and Methanomicrobiales) and form distinct phylogenetic clusters of mostly uncultivated archaea that are often unique to the intestinal tract of insects. The oxygen-reducing capacities of the few available isolates and their location in the microoxic gut periphery indicate that at least some species of this notoriously oxygen-sensitive group are well adapted to the continuous influx of oxygen into their habitat. Although colonization by methanogens seems to require a predisposition of the host, possible benefits for the insect remain to be discovered. The high methane emissions of termites, together with their enormous biomass especially in tropical regions, make them a significant natural source of this important greenhouse gas.
