Modulation of dimethylsulfoniopropionate (DMSP) concentration in an Alexandrium minutum (Dinophyceae) culture by small-scale turbulence: A link to toxin production?

Abstract

Some marine dinoflagellates produce important amounts of dimethylsulfoniopropionate (DMSP), a common compatible solute, and its cleavage product dimethylsulfide (DMS), a climatically active trace gas. In the field, dinoflagellate proliferations appear to be favored by calm weather and water column stability; indeed, small-scale turbulence is a physical factor that directly affects ecophysiological aspects of this phytoplankton group, including toxin production. Here we report the effect of experimentally generated turbulence on DMSP production by a paralytic shellfish poisoning (PSP) toxin producing strain of Alexandrium minutum, a widespread bloomforming dinoflagellate species. With respect to still conditions, the populations exposed to turbulence grew at a slower growth rate and yielded low cell numbers turbulence. Concurrently, the cellular DMSP concentration increased by ca. 20% (from 0.22 ± 0.01 to 0.27 ± 0.03 fmol μm −3 on a cell volume basis) in the shaken cultures. DMSP was preferentially synthesized during the light period in both treatments. During the night, a slowdown of the division process caused DMSP accumulation in the cells exposed to shaking. The study suggests the existence of a tight link between the dynamics of DMSP concentration and other cell processes entrained by circadian rhythms in dinoflagellates. The observed effects of small-scale turbulence on the DMSP dynamics supports the suggested role of this compound as an overflow mechanism in metabolically unbalanced cells. Furthermore, considering all the effects on the physiology of A. minutum exposed to the same experimental setup, we propose a possible link between the DMSP and the PSP metabolisms.