Seasonal variations in the contributions of different bacterial groups to the uptake of low-molecular-weight compounds in northwestern Mediterranean coastal waters - PubMed (original) (raw)

Seasonal variations in the contributions of different bacterial groups to the uptake of low-molecular-weight compounds in northwestern Mediterranean coastal waters

Laura Alonso-Sáez et al. Appl Environ Microbiol. 2007 Jun.

Abstract

We analyzed the contributions of different heterotrophic bacterial groups to the uptake of several low-molecular weight compounds during a seasonal cycle on the northwestern Mediterranean coast (Blanes Bay Microbial Observatory). The bacterial assemblage structure had been shown to change substantially year-round for this site, but whether changes in the activities of the different bacterial groups also occurred on the seasonal scale was unknown. Microautoradiography combined with catalyzed reporter deposition fluorescence in situ hybridization was used to analyze the patterns of glucose, amino acid, and ATP uptake by different bacterial groups. Gammaproteobacteria and Bacteroidetes were not very active in the uptake of glucose at any time of the year (<10% of cells were active) compared to Alphaproteobacteria (generally >20% of cells were active). Dissolved free amino acids were taken up considerably by Alphaproteobacteria and Gammaproteobacteria but not by Bacteroidetes. Relatively high percentages of cells of the three broad phylogenetic groups actively took up ATP, which could be related to the important phosphorous limitation of bacterial production during most of the year in Blanes Bay. The contribution of SAR11 to the uptake of the monomers was variable year-round, generally with fewer than 30% of the cells being active. By contrast, Roseobacter were highly overrepresented in the uptake of all the substrates throughout all the year, with more than 50% of cells being active in all the samples and for all substrates. Our results suggest that substantial changes in the activity of some phylogenetic groups of bacteria occur throughout the year.

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Figures

FIG. 1.

FIG. 1.

Temperature, Chl a, and phosphate concentrations throughout the seasonal study at Blanes Bay. The arrows indicate the dates at which samples were taken for MAR-CARD-FISH analyses.

FIG. 2.

FIG. 2.

Year-round rates of bulk substrate uptake in Blanes Bay and percentage of EUB+ cells actively incorporating each of the substrates (bars). Samples taken in July are presented as outliers, since the bacterial assemblage structure and carbon dynamics drastically changed in this sampling (5).

FIG. 3.

FIG. 3.

Seasonal dynamics of the percentages of probe-positive cells (Alphaproteobacteria, Roseobacter, SAR11, Gammaproteobacteria, and Bacteroidetes) active in the uptake of the three substrates (glucose, amino acids, and ATP). Individual data points are shown for those samples for which replicates or triplicates were counted.

FIG. 4.

FIG. 4.

Contributions of various phylogenetic groups (SAR11, Roseobacter [Ros], Gammaproteobacteria [Gam], and Bacteroidetes [Bcdt]) to assemblage structure, presented against their contributions to the uptake of glucose, amino acids, and ATP in Blanes Bay. Percentages were calculated relative to eubacterial cells (probes EUB338-II and -III).

FIG. 5.

FIG. 5.

Abundances of cells of the phylogenetic groups Alphaproteobacteria (Alpha), Gammaproteobacteria (Gam), Bacteroidetes (Bcdt), Roseobacter (Ros), and SAR11 that were active in the uptake of glucose, amino acids, and ATP.

FIG. 6.

FIG. 6.

Seasonal contribution of each of the analyzed phylogenetic groups (SAR11, Roseobacter [Ros], other Alphaproteobacteria [Alpha], Bacteroidetes [Bcdt], and Gammaproteobacteria [Gam]) to total active bacteria in the uptake of glucose, amino acids, and ATP in Blanes Bay. Percentages were calculated relative to eubacterial cells (probes EUB338-II and -III).

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