High rate of uptake of organic nitrogen compounds by Prochlorococcus cyanobacteria as a key to their dominance in oligotrophic oceanic waters - PubMed (original) (raw)

High rate of uptake of organic nitrogen compounds by Prochlorococcus cyanobacteria as a key to their dominance in oligotrophic oceanic waters

Mikhail V Zubkov et al. Appl Environ Microbiol. 2003 Feb.

Abstract

Direct evidence that marine cyanobacteria take up organic nitrogen compounds in situ at high rates is reported. About 33% of the total bacterioplankton turnover of amino acids, determined with a representative [(35)S]methionine precursor and flow sorting, can be assigned to Prochlorococcus spp. and 3% can be assigned to Synechococcus spp. in the oligotrophic and mesotrophic parts of the Arabian Sea, respectively. This finding may provide a mechanism for Prochlorococcus' competitive dominance over both strictly autotrophic algae and other bacteria in oligotrophic regions sustained by nutrient remineralization via a microbial loop.

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Figures

FIG. 1.

FIG. 1.

[35S]methionine uptake by total bacterioplankton collected at different depths and by flow cytometrically sorted general bacterial cells (all bact) and Prochlorococcus (Pro). Prochlorococcus was sorted from the replicated fixed samples on two successive days (s.I and s.II). (a) Time series; (b) sorted cell number series. Dashed lines show linear regressions (Regr.), and corresponding regression coefficients (_r_2) are presented in the keys. DPM, disintegrations per minute.

FIG. 2.

FIG. 2.

Characteristic flow cytometric signatures of natural bacterioplankton in oligotrophic (a to c) and mesotrophic (d to f) regions of the Arabian Sea. Clearly revealed bacterioplankton cells stained for DNA were gated by the polygons (a and d) for radiolabel sorting to determine [35S]methionine uptake by an average bacterioplankton cell. The bacterial cells within the polygons were plotted separately to show Prochlorococcus (Pro) (b) and Synechococcus (Syn) (e) clusters with extra red fluorescence. The clusters of Prochlorococcus (c) and Synechococcus (f) sorted for radiolabel analyses were plotted separately.

FIG. 3.

FIG. 3.

Comparison of [35S]methionine uptake rates of flow-sorted Prochlorococcus and Synechococcus cells with uptake rates of average bacterioplankton cells (a) as well as vertical distributions of cyanobacterial methionine turnover (b) and its comparison with total bacterioplankton turnover (c). The uptake rates of average bacterioplankton cells were determined by flow sorting of the whole bacterioplankton community. Error bars indicate a single standard error of three measurements. Dashed line indicates a unity line. d, days. Data derived from Prochlorococcus sorted from the partially resolved clusters are shown by open circles and from the complete clusters by filled circles. DPM, disintegrations per minute.

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