Latitudinal and vertical distributions of particle-associated dimethylsulfoniopropionate (DMSP) lyase activity in the western North Atlantic Ocean

Abstract

Dimethylsulfoniopropionate (DMSP) lyase enzymes cleave phytoplankton-derived DMSP into dimethylsulfide (DMS) and acrylate. We measured particle-associated (>0.7 µm) DMSP lyase activity (DLA) in diverse waters from the Gulf of Maine to the Sargasso Sea. DLA fell within a relatively narrow range (0.63–5.4 nmol DMS·L–1·min–1), with no significant geographic trend. DLA was, however, generally highest near the surface and decreased with depth within the euphotic zone. When normalized to chlorophyll a (Chl a), DLA was significantly higher in oligotrophic surface waters of the Sargasso Sea (DLA:Chl a = 33–53 nmol DMS·min–1·µg Chl a–1) compared with more productive Gulf of Maine waters (DLA:Chl a = 0.5–7.9 nmol DMS·min–1·µg Chl a–1). In optically clear waters of the Sargasso Sea, DLA:Chl a was generally highest near the surface and decreased with depth, following a similar trend to that of the photoprotective pigment diadinoxanthin. When ammonium and phosphate were added to oligotrophic water from the Sargasso Sea, Chl a increased exponentially, whereas DLA:Chl a decreased by 83%. Our results suggest that Chl a specific DLA is highest when plankton are exposed to high solar radiation and low nutrients, consistent with the idea that DMSP lyases may be involved in oxidative stress protection.