Molecular diversity of bacterial production of the climate-changing gas, dimethyl sulphide, a molecule that impinges on local and global symbioses.

This paper describes the ddd genes that are involved in the production of the gas dimethyl sulphide from the substrate dimethylsulphoniopropionate (DMSP), an abundant molecule that is a stress protectant in many marine algae and a few genera of angiosperms. What is known of the arrangement of the ddd genes in different bacteria that can undertake this reaction is reviewed here, stressing the fact that these genes are probably subject to horizontal gene transfer and that the same functions (e.g. DMSP transport) may be accomplished by very different mechanisms. A surprising number of DMS-emitting bacteria are associated with the roots of higher plants, these including strains of Rhizobium and some rhizosphere bacteria in the genus Burkholderia. One newly identified strain that is predicted to make DMS is B. phymatum which is a highly unusual beta-proteobacterium that forms N(2)-fixing nodules on some tropical legumes, in this case, the tree Machaerium lunatum, which inhabits mangroves. The importance of DMSP catabolism and DMS production is discussed, not only in terms of nutritional acquisition by the bacteria but also in a speculative scheme (the 'messy eater' model) in which the bacteria may make DMS as an info-chemical to attract other organisms, including invertebrates and other plankton.