Continental-scale Temporal Monitoring of Marine Dimethylsulphoniopropionate Degraders

Dimethylsulphoniopropionate (DMSP) is emerging as a significant metabolite that facilitates climate-relevant interactions between DMSP-producing phytoplankton and DMSP-degrading bacteria. An impressive abundance and diversity of bacteria have genes that encode DMSP degradation, notably the SAR11 and Roseobacter clades. Recent research on the micro-diversity of bacterial DMSP regulatory genes reported correlations between strain-specific DMSP degradation genes and phytoplankton. Here we explore if taxon-specific interactions between phytoplankton and DMSP degrading bacteria are affected by environmental shifts that occur over space and time, and in turn, how changes in the microbial community influence DMSP cycles. Seven concurrent coastal time-series spanning tropical, subtropical and temperate environments were subject to monthly or seasonal sampling of 18S, 16S and metagenomic sequences between June 2015 and July 2017 (120 dates sampled, n = 749). Our results indicate significant co-occurrence between exact sequence variants of Roseobacter with genera of phytoplankton with high DMSP producing potential, including Micromonas and Phaeocystis. Using Metagenomic analysis we highlight the distribution of DMSP regulatory genes within seasonally dominant bacterial taxa and mapping approaches found that spatiotemporal patterns exist in the distribution of the bacterial DMSP demethylase gene (dmdA). Further support for DMSP-mediated interactions between phytoplankton and DMSP degrading bacteria was evidenced by significant positive correlations between dmdA and the phytoplankton pigment chlorophyll a. The temporal variability of bacterial DMSP degradation genes and its effect on DMSP cycles was further investigated with a time-series in subtropical surface waters. Gas chromatography and quantitative polymerase chain reaction was used to assess how the total abundance and expression of dmdA and the bacterial DMSP lyase gene (ddd) influences surface water concentrations of dimethylated sulphur. By using bioinformatic, biogeochemical and molecular approaches with sustained observations we provide a rare insight into the spatial and temporal variability of DMSP cycling across multiple marine provinces.