Zero-valent sulphur and marine methane oxidation

Abstract

In marine sediments, anaerobic oxidation of methane (AOM) coupled to sulphate reduction was thought to be carried out by a consortium of methanotrophic archaea (ANME) and co-occurring sulphate-reducing deltaproteobacteria, but the mechanistic details of this partnership had not been resolved. Now, Milucka et al. show that ANME carry out AOM as well as dissimilatory sulphate reduction to form disulphide and other zero-valent sulphur compounds. Instead of carrying out the coupled sulphate reduction processes, as previously expected, the deltaproteobacteria in the culture took up the disulphide produced by ANME, and this disulphide was then disproportionated to sulphide and sulphate, the latter of which could feed back to ANME for further rounds of AOM. These studies provide the first evidence for the direct formation of zero-valent sulphur compounds during sulphate reduction and reveal that AOM is not necessarily an obligate syntrophic process between ANME and deltaproteobacteria. The precise details of the enzymatic pathways involved in dissimilatory sulphate reduction by ANME remain to be determined.