Salinity and growth effects on dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) cell quotas of Skeletonema costatum, Phaeocystis globosa and Heterocapsa triquetra

Abstract

The effects of growth stage and salinity on dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) cellular content were investigated in laboratory batch cultures of three phytoplankton species (Skeletonema costatum, Phaeocystis globosa and Heterocapsa triquetra). DMSP and DMSO cell quotas of the three microalgae were measured at three salinities (20, 27, 35) and in three growth phases at salinity 35. DMSP and DMSO cell quotas varied along the growth for all species with an increase of DMSP for S. costatum and a decrease of the DMSP to DMSO ratio (DMSP/DMSO) for P. globosa and H. triquetra in late exponential-stationary phase. We hypothesized that the oxidative stress caused by light and/or nutrients limitation induced the oxidation of DMS or DMSP to DMSO. DMSP cell quotas increased with salinity, mostly in S. costatum and H. triquetra, for which DMSP is supposed to be an osmoregulator. In H. triquetra, DMSO cell quotas stayed constant with increasing salinity. DMSO was near detection limits in S. costatum experiments. In P. globosa, DMSP and DMSO concentrations increased at low and high salinity. DMSO showed higher increase at low salinity presumably as the result of a salinity-induced oxidative stress which caused DMSP oxidation into DMSO in hyposaline conditions. We concluded that DMSP acts as an osmoregulator for the three studied species and DMSO acts as an antioxidant for P. globosa at low salinity. In P. globosa and H. triquetra, DMSP/DMSO increase with salinity in response to salinity stress.