Bacterial uptake of low molecular weight organics in the subtropical Atlantic: Are major phylogenetic groups functionally different?

Laura Alonso-Sáez, Olga Sánchez and Josep M. Gasol

Limnol. Oceanogr., 57(3), 2012, 798-808 | DOI: 10.4319/lo.2012.57.3.0798

ABSTRACT: We present measurements of glucose, amino acids, and adenosine triphosphate (ATP) bacterial uptake at tracer concentrations across an oceanic gradient from the Cape Blanc upwelling to the Northeast Atlantic subtropical gyre. The bulk uptake of the compounds increased in the upwelling, with amino acids being the most actively taken up substrate (up to 20 pmol L-1 h-1). The single-cell activity of the bacterial groups also increased in the upwelling, particularly for Rhodobacteraceae (up to 94% of active cells), but this group had low activity in oligotrophic waters (< 10% of active cells), which suggests it is exclusively adapted to high-nutrient conditions. The percentage of SAR11 active cells was relatively high in the upwelling area, particularly for glucose and amino acid uptake (up to 53% of active cells), which suggests that some members of this group are also adapted to nutrient-rich environments. Of the broad phylogenetic groups tested, Bacteroidetes were the least active and Alpha- and Gammaproteobacteria showed similar percentages of active cells in amino acid uptake (∼ 30%). Alphaproteobacteria had the highest percent of cells involved in glucose uptake, while Gammaproteobacteria dominated ATP uptake. This general pattern was confirmed in a broader analysis that included data from contrasting marine environments, which suggests that major phylogenetic groups of bacteria participate differently in the turnover of these low-molecular-weight organics. Our results support the view that broad phylogenetic groups can be identified within the bacterial ‘black box’ with different patterns in the cycling of organic matter. Analyzing them may help us understand, and ultimately predict, oceanic carbon processing.

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