Testing the potential ballast role for dimethylsulfoniopropionate in marine phytoplankton: a modeling study

Abstract

The increase in dimethylsulfoniopropionate (DMSP) biosynthesis measured in several nitrogen-limited marine algae may partially replace other less dense organic solutes such as glycine betaine (GBT). This raises the possibility that phytoplankton could synthesize the denser organic solute DMSP in low nutrient oceanic surface waters facilitating sinking into zones of the euphotic zone richer in nutrients and maximizing their growth, hereafter referred to the “DMSP-ballast” hypothesis. The objective of this study was to test the DMSP-ballast hypothesis by modeling the sinking rates of the diatom Thalassiosira pseudonana and two strains of the coccolithophore Emiliania huxleyi as a function of DMSP synthesis in nitrogen-limited conditions. We also explored the potential ballast effect of DMSP in the positively buoyant non-motile algal species Ethmodiscus rex and Pyrocystis noctiluca. The model results suggest that replacement of trimethylammonium and GBT by DMSP in the naked E. huxleyi strain and T. pseudonana grown under nitrogen limitation could increase the sinking rate by 1 – 22%; while a putative increase in DMSP synthesis (in the millimolar range) in E. rex and P. noctiluca could decrease the rising rate by 43% to several orders of magnitude. The present study suggests a potential ballast role for DMSP in phytoplankton.