Sequencing the Sea Sulphur Cycle

Picture this. A molecule, quite a simple one, which charms the sea birds in distant seas, which makes tiny shrimps tumble in excitement at getting their lunch and, which causes the billowing clouds to form over the far-flung oceans. And, as if that were not enough, every time you stroll by the seaside, that tangy, evocative aroma is due not to the ozone your parents told you about, or the Calvin Klein 'Ocean' deodorant in 'Seinfeld' (listen to; http://podcast.sciam.com/daily/sa_d_podcast_070209.mp3), but to this marvellous little substance, a gas called DIMETHYL SULPHIDE. The rather unlikely starting point for this remarkable compound is another molecule, called dimethylsulphoniopropionate (DMSP for short) which is used by huge numbers of marine plankton and seaweeds as an anti-stress protectant. When these plants die, they release the DMSP and this is then latched onto by bacteria, which break it down, using part of it for their carbon and sulphur food requirements. Worldwide, this occurs at a prodigious scale, with more than 400 million tonnes of DMSP being shifted by bacterial action every year. One product of the breakdown process is the magical DMS, some of which is released into the air, causing, among other things, the characteristic smell of the seaside. Remarkably, some ocean seabirds, such as petrels and shearwaters, sense the DMS as a marker for food supplies and home in on it from miles away. And, on a different scale, tiny, but hugely abundant shrimp-like creatures called copepods can also use DMS to indicate nearby food supplies. More important, though, DMS is further modified in the atmosphere, to sulfate aerosols, which act as nucleating agents to form clouds over the oceans, in the same way (sort of) as one gets crystals to grow in a crystal garden by starting off with a 'seed'. This has major effects on global climate and was even used by that sage, James Lovelock, as a plank to underpin his 'Gaia Hypothesis'. Although the production and subsequent conversions of DMS are hugely important, in many ways, we know very little about how these processes occur, at least at molecular levels. However, recent work by the applicants has unravelled at least some of the steps by which DMS is made and by which it is then transformed into other sulphurous compounds. Very suprisingly, though, that work also showed that there are several different ways in which different species of marine bacteria can undertake these reactions. So, we now wish to know the entire genetic makeup of these intriguing, and important bacteria so that we can unravel just what lies behind their remarkable metabolic flexibility. By having the entire sequences of their genomes, we will have a great set of resources to help us, and others in the marine microbiology world, to understand far better what is going on, at a local and a global level in the formation and biochemical and environmental fate of the DMS gas.