Organizing principles in the nitrogen–carbon landscape of marine heterotrophic bacteria

Marine microbes metabolize a wide range of carbon and nitrogen sources, shaping global biogeochemical cycles. Despite being crucial at the global scale, the coupling between carbon and nitrogen remains poorly understood at the level of individual metabolites and bacteria. By phenotyping a library of marine heterotrophic bacteria across increasingly complex carbon and nitrogen sources, we generated a snapshot of this coupling. Growth phenotypes were weakly explained by phylogeny, but could be organized around substrate properties, including C:N stoichiometry and degree of reduction. Beyond explainable average trends along these axes, different strains displayed significant variability. For some bacteria, nitrogen use efficiency was associated with ammonium secretion, consistent with their role in ecological interactions. Furthermore, nonlinearities emerged in how yields depend on combinations of resources, such as mixtures of amino acids and dipeptides. These organizing principles may help understand the ecological role of marine heterotrophic bacteria and parametrize models of biogeochemical cycles.