What is known about DMSO?

DMSO is a stable non-volatile compound that is ubiquitous in seawater. It is usually found in concentrations greater than DMS in surface and euphotic waters with levels ranging from 2 to 26 nmol L^-1. DMSO can also be detected at greater depths than either DMS or DMSP, the known biological precursor of DMS in seawater

Photochemical formation

Relatively little is known about the production, cycling and fate of DMSO in natural waters or whether it is a significant sink or source of DMS in the oceans. It is clear that DMS can be photo-oxidised to DMSO in the presence of dissolved organic carbons, such as humic acid (A), but to date, DMSO has only been measured as a minor product, accounting for 14% of all the DMS photochemically removed.

Bacterial transformations

Some marine bacterial aerobes and anaerobes are able to oxidise DMS to DMSO using DMS as an electron donor (B). Others can use DMSO as an electron acceptor and reduce DMSO to DMS (C). DMSO can also be used as a carbon source for growth without the production of DMS. However, although these bacterial transformations have been shown in the laboratory, it is not known how significant they are in natural seawater.

Biosynthesis by phytoplankton

There is increasing evidence to suggest DMSO is directly biosynthesised by phytoplankton (D). The presence of DMSO in particulate matter has been associated to phytoplankton during laboratory growth studies and in natural seawater samples, with concentrations ranging from <2 - 110 nmol L^-1. Thus, phytoplankton could be a significant source of DMSO in the oceans. After its reduction to DMS by bacteria, DMSO from cells could be a alternative pathway of DMS production in seawater.

Current Research

DMSO is currently measured using the enzyme DMSO reductase, purified (in house) from the purple non-sulphur bacterium Rhodobacter capsulatus. The resulting DMS is then analysed by Gas Chromatograpy and flame photometric detection. Current research involves developing a method suitable to measure DMSO in the cells of phytoplankton and using this to investigate the mechanisms through which DMSO may be released from algae in laboratory cultures and natural seawater mesocosms. Research will also determine how DMSO is formed in cells and the production of DMSO through abiotic photochemical processes in seawater.