Combining cell sorting with gas chromatography to determine phytoplankton group-specific intracellular dimethylsulphoniopropionate

Abstract

An approach combining flow-cytometric fluorescence-activated cell sorting (FACS) of specific phytoplankton groups and subsequent quantification of dimethylsulphoniopropionate (DMSP) content by gas chromatography (GC) is introduced and applied to cultivated microalgae and natural seawater samples. The FACS-GC based method produces statistically robust estimates of the intracellular DMSP content of a variety of phytoplankton groups ranging from prokaryotic Synechococcus spp. to eukaryotic nanophytoplankton. Comparison between FACS and traditional filtration approaches to determine intracellular DMSP content of cultivated microalgae illustrates variable responses between species to the 2 methods. Natural photosynthetic nanoeukaryote populations contained high intracellular DMSP content; comparable to many cultivated prymnesiophyte taxa. A surprisingly high DMSP content was found in natural populations of Synechococcus spp., in contrast to previous values measured in cultivated strains, but possibly confirming the uptake and retention of DMSP by this photosynthetic prokaryote. When combined, the DMSP contributions of each phytoplankton group amounted to between 40 and 57 % of total DMSP in each water sample, with the bulk of the total comprising nanoeukaryote-DMSP. The approach has high potential to provide information that enables better parameterisation of phytoplankton functional types in mechanistic dimethyl sulphide models and to help elucidate the environmental controls that govern the extent and diversity of DMSP production in the oceans.