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 theproduction of the gas dimethyl sulphide from the substrate dimethylsulphoniopropionate(DMSP), an abundant molecule that is a stress protectant inmany marine algae and a few genera of angiosperms. What is knownof the arrangement of the ddd genes in different bacteria thatcan undertake this reaction is reviewed here, stressing thefact that these genes are probably subject to horizontal genetransfer and that the same functions (e.g. DMSP transport) maybe accomplished by very different mechanisms. A surprising numberof DMS-emitting bacteria are associated with the roots of higherplants, these including strains of Rhizobium and some rhizospherebacteria in the genus Burkholderia. One newly identified strainthat is predicted to make DMS is B. phymatum which is a highlyunusual β-proteobacterium that forms N₂-fixing noduleson some tropical legumes, in this case, the tree Machaeriumlunatum, which inhabits mangroves. The importance of DMSP catabolismand DMS production is discussed, not only in terms of nutritionalacquisition by the bacteria but also in a speculative scheme(the ‘messy eater’ model) in which the bacteriamay make DMS as an info-chemical to attract other organisms,including invertebrates and other plankton. Key words: Acyl CoA transferase, Burkholderia, CLAW hypothesis, dimethyl sulphide, dimethylsulphoniopropionate, Marinomonas, nitrogen fixation, Rhizobium, rhizosphere, root nodules, Spartina Received 30 May 2007; Revised 27 September 2007 Accepted 1 October 2007