Strong linkages between DOM optical properties and main clades of aquatic bacteria

Despite considerable research on the linkages between dissolved organic matter (DOM) and bacteria, it is not yet clear how the abundance of the main aquatic clades relates to DOM composition in natural aquatic systems. We evaluated this relation using PARAFAC modeling of excitation-emission fluorescence spectroscopy and spectroscopic indexes to characterize DOM composition, and fluorescence in situ hybridization, to quantify the major bacterial groups in a subtropical lagoon. The DOM exhibited marked temporal variations in concentration, molecular weight, aromaticity, color, degree of humification, and freshness, and proportion of the three different fluorescent components identified. All major bacterial clades (Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Cytophaga-Flavobacteria) were significantly linked to DOM concentration and/or composition, being those crucial factors for modeling their abundance in situ. The combination and significance of the factors was specific for each bacterial group, strongly indicating that they behave as coherent and distinctive units. Cytophaga-Flavobacteria and Betaproteobacteria were the groups which correlated with more DOM properties. Alphaproteobacteria and Gammaproteobacteria abundances were significantly explained by low or high dissolved organic carbon concentrations, respectively. The significant relationships between DOM properties and the main bacterial groups delineated a profile of each group regarding DOM preferences/dislikes, in agreement with evidence derived from genome analysis to single-cell substrate uptake. These results highlight the specificities of the main bacterial clades, providing support for a functional classification of the bacterioplankton regarding DOM processing at the level of bacterial classes.