Dimethylsulfide sources from microalgae: Improvement and application of a derivatization-based method for the determination of dimethylsulfoniopropionate and other zwitterionic osmolytes in phytoplankton

Dimethylsulfoniopropionate (DMSP) is a metabolite involved in central processes of phytoplankton physiology and ecology. Due to its high abundance, this molecule plays also a major role in global sulfur cycling. DMSP concentrations are usually indirectly determined via the base mediated release of dimethylsulfide (DMS) using gas chromatography (GC). However, because other potential precursors of DMS have been reported from macroalgae and phytoplankton, there is a substantial risk for an overestimation using an indirect method. We improve and validate a protocol for the derivatization and determination of DMSP in phytoplankton cultures. The improved method includes derivatization with 1-pyrenyldiazomethane (PDAM) and analysis via ultra performance liquid chromatography coupled with a mass selective detector (UPLC/MS). The protocol allows simultaneous qualitative and quantitative analysis of DMSP, other putative DMS precursors and osmolytes like glycine betaine (GBT). Detection limits are around 100 fmol on column allowing the quantification of DMSP from plankton field samples as well as from phytoplankton cultures. The DMSP content of several phytoplankton cultures was determined using the method involving derivatization of DMSP as well as an indirect headspace method determining DMS. For several algae strains, significant higher concentrations were obtained with the indirect determination. These results underscore the importance of other potential DMS precursors in phytoplankton samples that are not considered when using indirect methods for DMSP determination.