The importance of dimethylsulfide (DMS) for processes in the marine atmosphere is well established. However, the enzymatic cleavage of dimethylsulfoniopropionate (DMSP) to DMS, acrylate and a proton is not well understood. DMSP cleaving enzymes (DMSP lyases) are not limited only to few DMSP producing algae but may be abundant in many marine taxa. The phytoplankton Phaeocystis spec. and Emiliania huxleyi are high producers of DMSP and responsible for an increased flux of sulfur into the marine atmosphere. Both species have DMSP lyases that differ considerably in their requirements for optimal activity. DMSP contributes to osmotic equilibrium of algal cells and under low temperatures it may prevent damage or activity loss in enzyme systems essential for cell survival. However, most DMSP producing phytoplankton may never experience changes in salinity or temperature. Therefore, there must be other benefits to phytoplankton cells to produce and intracellularly accumulate mM concentrations of DMSP.

Grazing of the herbivorous dinoflagellate Oxyrrhis marina on Emiliania huxleyi results in high production of DMS after ingestion of cells. It appears that DMSP and DMSP lyase are segregated inside the cells and may only react after mechanical or chemical stress and resulting loss of cell integrity. Such a mixing occurs in the food vacuoles of O. marina where 65 mM DMS is produced during 5 min after ingestion of E. huxleyi cells. Assuming that the same amount of acrylate is being produced, acrylate may accumulate to concentrations with potentially toxic side-effects. Therefore, DMSP cleavage may be used to deter predators and to reduce grazing pressure on phytoplankton communities.

DMSP lyases in crude extracts of six different strains of Emiliania huxleyi showed high variability with respect to absolute activity, and pH and NaCl requirements for optimal DMSP cleavage. This has implications for the DMS production in situ: Similar concentrations of particulate DMSP may not be used as a proxy for DMS production, because this process depends on the activity and requirements of algal DMSP lyases present. However, what parameters influence the relative abundance of DMSP lyase activity is still unknown.

The cleavage of DMSP to DMS, acrylate and a proton may also be used to acidify cell compartments or a microenvironment surrounding individual cells or cell colonies. A decreased pH on the surface of phytoplankton cells would have implications for the relative abundance of seawater carbon species. More CO2 would become available from HCO3-, the dominant carbon species at seawater pH. This would result in an increased flux of CO2 into the cells. With this mechanism DMSP producing algae may benefit in situations where CO2 becomes a limiting factor for growth. The possible role of DMSP in forming microenvironments with low pH is unknown but this highlights the demand of further investigations on the multifunctional compound DMSP.