DIMETHYLSULFONIOPROPIONATE CLEAVAGE BY MARINE PHYTOPLANKTON IN RESPONSE TO MECHANICAL, CHEMICAL, OR DARK STRESS1

Abstract

Several bloom‐forming marine algae produce concentrated intracellular dimethylsulfoniopropionate (DMSP) and display high DMSP cleavage activity in vitro and during lysis after grazing or viral attack. Here we show evidence for cleavage of DMSP in response to environmental cues among different strains of the haptophyte Emiliania huxleyi (Lohmann) Hay et Mohler and the dinoflagellate Alexandrium spp. (Halim). Sparging or shaking live cells of either taxon increased dimethyl sulfide (DMS), especially in dinoflagellates, known to be very sensitive to shear stresses. Additions of polyamines, known triggers of exocytosis in some protists, also stimulated DMSP cleavage in a dose‐responsive manner. We observed DMS production by some algae after shifts in light regime. When most exponential‐phase E. huxleyi were transferred to continuous darkness, cells decreased in volume and DMSP content within 24 h; DMSP content per unit cell volume remained relatively steady. DMS accumulated as long as cells remained in the dark, but on returning to a light:dark cycle DMS accumulation ceased within 24 h. However, E. huxleyi strain CCMP 373, containing highly active in vitro DMSP lyase, produced only transient accumulations of DMS in the dark. This was apparently due to production and concomitant oxidation or uptake of DMS, because cells of this strain rapidly removed DMS added to cultures. Three strains of the dinoflagellate Alexandrium tamarense containing high in vitro DMSP lyase activity showed no DMS production in the dark, and all appeared to remove additions of DMS. Alexandrium tamarense strain CCMP 1771 also removed dimethyl disulfide, an inhibitor of bacterial DMS consumption. These data suggest that physical or chemical cues can trigger algal DMSP cleavage, but DMS production may be masked by subsequent oxidation and/or uptake.