Microbial degradation of methanesulphonic acid: a missing link in the biogeochemical sulphur cycle

Abstract

ATMOSPHERIC dimethyl sulphide, arising from marine algae, cyanobacteria and salt marsh plants such as Spartina, is the principal sulphur compound entering the atmosphere from terrestrial and aquatic environments ^1–6. Methanesulphonic acid (CH₃SO₃H; MSA) has been identified as a major product of the photochemical oxidation in the atmosphere of dimethyl sulphide^{1–3,5,7–9}. Dimethyl sulphide and MSA are thus predominantly, if not exclusively, biogenic in origin, and are the main gaseous links in the biogeochemical sulphur cycle. MSA is a stable compound, not undergoing photochemical decomposition³, so its removal from the atmosphere is by wet and dry deposition. MSA partitions into the aerosol phase, as well as nucleating droplet formation, and is deposited in rain and snow. Analysis of Antarctic ice cores¹⁰ gives evidence of its global deposition over many thousands of years. The subsequent fate of MSA deposited on land was unknown. Here we describe terrestrial bacteria that grow on MSA. Their activities in the natural environment would result in the mineralization of MSA to carbon dioxide and sulphate, thus completing our understanding of this part of the sulphur cycle.