Reduction of molecular sulphur by methanogenic bacteria

Abstract

Methanogenesis is the characteristic, energy-yielding metabolic pathway in methanogenic bacteria¹. Here we report that in the presence of molecular sulphur, these bacteria form large amounts of H₂S by dissimilatory sulphur reduction, in addition to methane. Thus, methanogenic bacteria may be responsible for formation of much of the H₂S found in their habitats (marine sediments, sewage digestors and solfataric springs—where sulphur is present), and they may also be responsible for corrosion which has previously been thought to be due exclusively to sulphate-reducing bacteria. These extremely oxygen-sensitive organisms could also create their own anaerobic environment by H₂S formation. As both groups of anaerobic archaebacteria—the anaerobic thermoacidophiles² and the methanogens—are able to reduce molecular sulphur, there may be a closer evolutionary relationship between the two groups than has been previously believed. Sulphur reduction seems to be a primitive means of energy conservation, and may have been the forerunner of energetically more efficient³ methanogenesis.