You exude what you eat: How carbon, nitrogen and sulfur rich organic substrates shape microbial community composition and the dissolved organic matter (DOM) pool

Phytoplankton are the major source of labile organic matter in the sunlit ocean, and they are therefore key players in most biogeochemical cycles. However, studies examining the heterotrophic bacterial cycling of specific phytoplankton derived nitrogen (N)- and sulfur (S)-containing organic compounds are currently lacking at the molecular level. Therefore, the present study investigated how the addition of N-containing (glycine betaine, GBT) and S-containing (dimethylsulfoniopropionate, DMSP) organic compounds, as well as glucose, influenced the microbial production of new organic molecules and the microbial community composition. The chemical composition of microbial produced DOM was analyzed by ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) demonstrating that CHO, CHON and CHOS containing molecules were enriched in the glucose, GBT and DMSP experiments, respectively. High-throughput sequencing showed that Alteromonadales was the dominant group in the glucose, while Rhodobacterales was the most abundant group in both the GBT and DMSP experiments. Co-occurrence network analysis furthermore indicated more complex linkages between the microbial community and organic molecules in the GBT compared with the other two experiments. Our results shed light on how different microbial communities response to distinct substrates and mediate the cycling of organic compounds.