Methane-consuming archaebacteria in marine sediments

Large amounts of methane are produced in marine sediments but are then cons umed before contacting aerobic waters or the atmosphere(1). Although no org anism that can consume methane anaerobically has ever been isolated, biogeo chemical evidence indicates that the overall process involves a transfer of electrons from methane to sulphate and is probably mediated by several org anisms, including a methanogen (operating in reverse) and a sulphate-reduce r (using an unknown intermediate substrate)(2). Here we describe studies of sediments related to a decomposing methane hydrate. These provide strong e vidence that methane is being consumed by archaebacteria that are phylogene tically distinct from known methanogens, Specifically, lipid biomarkers tha t are commonly characteristic of archaea are so strongly depleted in carbon -13 that methane must be the carbon source, rather than the metabolic produ ct, for the organisms that have produced them. Parallel gene surveys of sma ll-subunit ribosomal RNA (16S rRNA) indicate the predominance of a new arch ael group which is peripherally related to the methanogenic orders Methanom icrobiales and Methanosarcinales.