Resource Partitioning of Diatom Metabolites that Support Bacterial Heterotrophy in the Ocean (NMR assay)

The communities of marine bacteria that assemble around living microphytoplankton are predictably dominated by three taxonomic groups, each of which specializes in the use or transport of different components of the available metabolite pool: Rhodobacterales transport small and polar metabolites, Flavobacteriia use carbohydrate-rich polymers, and Gammaproteobacteria use compounds from both classes. The consistent ecological pattern involving these three taxa is widespread throughout the surface ocean, yet whether it reflects the outcome competition or niche partitioning of the phytoplankton-derived compounds is not clear. Addressing this question requires better knowledge than currently exists of the metabolites that link microbial autotrophs and heterotrophs in the surface ocean. Here we used two untargeted biological screening strategies that leverage bacterial proficiency for scavenging dilute substrates from chemically complex mixtures to characterize metabolite uptake by heterotrophic bacteria. In the first, expression patterns of transporters and diagnostic catabolic genes were analyzed in model marine bacteria grown individually in co-culture with the diatom Thalassiosira pseudonana. In the second, the ability of bacteria to draw down exometabolites from the culture medium was detected by novel approaches in mass spectrometry (MS) and nuclear magnetic resonance (NMR) analysis. These methods identified diverse chemical currencies mediating carbon transfer including low molecular weight metabolites (nucleosides, amino acids, organic acids, monomeric sugars, peptides, and sulfonates) and components of polysaccharides (chrysolaminarin, chitin oligomers, and alginate-like oligosaccharides). Bacterial utilization of bioreactive metabolites in the absence of competition indicated low resource overlap among strains and a dominance of resource partitioning over resource competition among the bacterial groups that process a major fraction of marine net primary production.

NMR assay is reported in the current study MTBLS1544
UPLC-MS assay is reported in MTBLS1751