Chemodiversity of Bacterial Exometabolomes and Marine Dissolved Organic Matter

Heterotrophic microorganisms in the ocean thrive on the diverse blend of organic compounds that make up marine dissolved organic matter (DOM). We hypothesize that bacteria - through uptake, transformation and release of organic compounds - play a key role in shaping the chemodiversity and functioning of marine DOM. To test this hypothesis, genome-sequenced strains of the Roseobacter group were incubated on defined single model substrates. The released exometabolomes were characterized at the molecular level by non-targeted Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and complementary analyses of amino acids and carbohydrates. The exometabolome composition of the tested strains was highly diverse and variable, and modulated by substrate and growth phase. Only a small fraction of the detected exometabolites matched genome-predicted metabolites of the investigated strains. The annotated compounds included precursors of vitamins, amino acids, growth factors, and quorum sensing-related compounds. Forming part of marine DOM, these exometabolites potentially support auxotrophic and prototrophic members of the marine microbial community. The extraordinary molecular diversity of compounds released by single bacterial strains highlights the potential role of microorganisms in the diversification of DOM. Considering the vast genetic repertoire of natural microbial communities, the multitude of available substrates and the complex interactions in marine environments, we propose that active microbial communities play a central role in producing and sustaining the observed chemodiversity of DOM in the ocean.