Ocean in a Bottle

Rachel Rogers and Jon Todd, co-authors on the study, demonstrate that lab work is no day at the beach. Credit: A. Johnston, University of East Anglia, UK

Friday, February 2nd, 2007--

Andrew Johnston and his colleagues have discovered how bacteria make the ocean smell like the ocean. “We’ve known that bacteria make it, we’ve even given names to some of the bacteria, but we’ve never known how,” says Johnston, a Professor of Biological Sciences at the University of East Anglia in the U.K..

The salty sea air smell can be traced to the gas dimethyl sulfide (DMS), Johnston says. DMS is derived from the molecule DMSP, which is produced by seaweed, phytoplankton and even some marsh plants to protect them against the stresses of life in the ocean.

When these plants and algae die, DMSP is released, at which point some bacteria come along and use it for energy, sometimes producing DMS in the process. “As they’re munching away through this DMSP—and they love it—one of the byproducts is this gas dimethyl sulfide,” Johnston explains.

Until this study, published in the journal Science this week, it was assumed that the DMSP molecule was split in two, with DMS going one way and another byproduct going the other. “People thought simplistically that an enzyme would just take the DMSP and just chop it in two bits.” Instead, Johnston says, the bacteria add a different molecule to the DMSP “to sort of soften it up, and then it gets broken down in a rather different way compared to what had been guessed at.”

To find the gene responsible for DMS production, Johnston and his colleagues swapped genes from bacteria they knew made DMS into E. coli bacteria. When E. coli started producing DMS, they knew they had found a winner. “We opened the bottle and we didn’t need any fancy machine or chromatograph, we could smell the damn thing. We sniffed it and …Oh My God, so this is E. coli smelling of the seaside.”

Just as DMS signals the ocean for humans, it draws other organisms to the sea as well. It is known as a chemo-attractant, luring sea birds—like shearwaters and petrels—and some crustaceans to sources of food. DMS means plankton, which often means dinner.

But DMS does more than perfume—it also makes clouds. When DMS floats into the atmosphere, it becomes oxidized, losing the S of DMS. The S, for sulfur, turns into sulfuric acid. The acid forms tiny droplets, to which water molecules attach, and that’s how clouds are made. Johnston says: “So if you see a cloud over the southern Atlantic or Pacific, then chances are it started out life forming around one of these little tiny droplets of oxidized DMS.”

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--Flora Lichtman