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Dominant oceanic bacteria secure phosphate using a large extracellular buffer.

Zubkov MV, Martin AP, Hartmann M, Grob C, Scanlan DJ - Nat Commun (2015)

Bottom Line: Furthermore, it seems that their phosphate uptake may counter-intuitively be lower in more productive tropical waters, as if their cellular demand for phosphate decreases there.Mathematical modelling is shown to support this conclusion.The fuller the buffer the slower the cellular uptake of phosphate, to the point that in phosphate-replete tropical waters, cells can saturate their buffer and their phosphate uptake becomes marginal.

View Article: PubMed Central - PubMed

Affiliation: National Oceanography Centre, Ocean Biogeochemistry &Ecosystems Research Group, European Way, Southampton SO14 3ZH, UK.

ABSTRACT
The ubiquitous SAR11 and Prochlorococcus bacteria manage to maintain a sufficient supply of phosphate in phosphate-poor surface waters of the North Atlantic subtropical gyre. Furthermore, it seems that their phosphate uptake may counter-intuitively be lower in more productive tropical waters, as if their cellular demand for phosphate decreases there. By flow sorting (33)P-phosphate-pulsed (32)P-phosphate-chased cells, we demonstrate that both Prochlorococcus and SAR11 cells exploit an extracellular buffer of labile phosphate up to 5-40 times larger than the amount of phosphate required to replicate their chromosomes. Mathematical modelling is shown to support this conclusion. The fuller the buffer the slower the cellular uptake of phosphate, to the point that in phosphate-replete tropical waters, cells can saturate their buffer and their phosphate uptake becomes marginal. Hence, buffer stocking is a generic, growth-securing adaptation for SAR11 and Prochlorococcus bacteria, which lack internal reserves to reduce their dependency on bioavailable ambient phosphate.

No MeSH data available.


Latitudinal distribution of cellular nutrient uptake and CO2 fixation rates of the two dominant bacterioplankton groups.Latitudinal distribution of nutrient uptake rates of SAR11 (a) and of nutrient uptake and CO2 fixation rates of Prochlorococcus (Pro) (b) cells in the North Atlantic subtropical gyre on the 2010 cruise. The nutrients were methionine (Met), ATP and inorganic phosphate (Pi). Only cellular uptake rates of inorganic phosphate (Pi 2012) were measured on the 2012 cruise. Black and grey dashed lines indicate median rates of Pi uptake in the phosphate-depleted centre of the gyre during the 2010 and 2012 cruises, respectively. Blue horizontal tick lines indicate boundaries of the central gyre. Error bars indicate propagated standard errors of combined measurements of microbial nutrient uptake rates, cell abundances and radiotracer concentrations in flow-sorted cells.
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f1: Latitudinal distribution of cellular nutrient uptake and CO2 fixation rates of the two dominant bacterioplankton groups.Latitudinal distribution of nutrient uptake rates of SAR11 (a) and of nutrient uptake and CO2 fixation rates of Prochlorococcus (Pro) (b) cells in the North Atlantic subtropical gyre on the 2010 cruise. The nutrients were methionine (Met), ATP and inorganic phosphate (Pi). Only cellular uptake rates of inorganic phosphate (Pi 2012) were measured on the 2012 cruise. Black and grey dashed lines indicate median rates of Pi uptake in the phosphate-depleted centre of the gyre during the 2010 and 2012 cruises, respectively. Blue horizontal tick lines indicate boundaries of the central gyre. Error bars indicate propagated standard errors of combined measurements of microbial nutrient uptake rates, cell abundances and radiotracer concentrations in flow-sorted cells.

Mentions: We used the modified Wright and Hobbie bioassay technique214 to estimate concentrations and microbial uptake rates of phosphate, amino acid—methionine (indication of microbial growth)—and ATP (indication of microbial organic phosphate acquisition; Supplementary Figs 3–5, see Methods for details). We flow sorted radiotracer-labelled cells to quantify Prochlorococcus and SAR11 group-specific uptake rates. First, we compared cellular uptake rates of phosphate with cellular uptake rates of other molecules to ascertain the extent of misbalance of molecule acquisition (Fig. 1), that is, do the cellular uptake rates of other molecules like amino acids or ATP or CO2 fixation (indication of phytoplankton growth) also decrease in more productive equatorial waters? Second, we carried out experiments using a 33P-phosphate pulse followed by a 32P-phosphate chase to determine the potential role of extracellular buffer in phosphate acquisition by Prochlorococcus and SAR11 (Supplementary Fig. 1, large and medium yellow squares).


Dominant oceanic bacteria secure phosphate using a large extracellular buffer.

Zubkov MV, Martin AP, Hartmann M, Grob C, Scanlan DJ - Nat Commun (2015)

Latitudinal distribution of cellular nutrient uptake and CO2 fixation rates of the two dominant bacterioplankton groups.Latitudinal distribution of nutrient uptake rates of SAR11 (a) and of nutrient uptake and CO2 fixation rates of Prochlorococcus (Pro) (b) cells in the North Atlantic subtropical gyre on the 2010 cruise. The nutrients were methionine (Met), ATP and inorganic phosphate (Pi). Only cellular uptake rates of inorganic phosphate (Pi 2012) were measured on the 2012 cruise. Black and grey dashed lines indicate median rates of Pi uptake in the phosphate-depleted centre of the gyre during the 2010 and 2012 cruises, respectively. Blue horizontal tick lines indicate boundaries of the central gyre. Error bars indicate propagated standard errors of combined measurements of microbial nutrient uptake rates, cell abundances and radiotracer concentrations in flow-sorted cells.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525184&req=5

f1: Latitudinal distribution of cellular nutrient uptake and CO2 fixation rates of the two dominant bacterioplankton groups.Latitudinal distribution of nutrient uptake rates of SAR11 (a) and of nutrient uptake and CO2 fixation rates of Prochlorococcus (Pro) (b) cells in the North Atlantic subtropical gyre on the 2010 cruise. The nutrients were methionine (Met), ATP and inorganic phosphate (Pi). Only cellular uptake rates of inorganic phosphate (Pi 2012) were measured on the 2012 cruise. Black and grey dashed lines indicate median rates of Pi uptake in the phosphate-depleted centre of the gyre during the 2010 and 2012 cruises, respectively. Blue horizontal tick lines indicate boundaries of the central gyre. Error bars indicate propagated standard errors of combined measurements of microbial nutrient uptake rates, cell abundances and radiotracer concentrations in flow-sorted cells.
Mentions: We used the modified Wright and Hobbie bioassay technique214 to estimate concentrations and microbial uptake rates of phosphate, amino acid—methionine (indication of microbial growth)—and ATP (indication of microbial organic phosphate acquisition; Supplementary Figs 3–5, see Methods for details). We flow sorted radiotracer-labelled cells to quantify Prochlorococcus and SAR11 group-specific uptake rates. First, we compared cellular uptake rates of phosphate with cellular uptake rates of other molecules to ascertain the extent of misbalance of molecule acquisition (Fig. 1), that is, do the cellular uptake rates of other molecules like amino acids or ATP or CO2 fixation (indication of phytoplankton growth) also decrease in more productive equatorial waters? Second, we carried out experiments using a 33P-phosphate pulse followed by a 32P-phosphate chase to determine the potential role of extracellular buffer in phosphate acquisition by Prochlorococcus and SAR11 (Supplementary Fig. 1, large and medium yellow squares).

Bottom Line: Furthermore, it seems that their phosphate uptake may counter-intuitively be lower in more productive tropical waters, as if their cellular demand for phosphate decreases there.Mathematical modelling is shown to support this conclusion.The fuller the buffer the slower the cellular uptake of phosphate, to the point that in phosphate-replete tropical waters, cells can saturate their buffer and their phosphate uptake becomes marginal.

View Article: PubMed Central - PubMed

Affiliation: National Oceanography Centre, Ocean Biogeochemistry &Ecosystems Research Group, European Way, Southampton SO14 3ZH, UK.

ABSTRACT
The ubiquitous SAR11 and Prochlorococcus bacteria manage to maintain a sufficient supply of phosphate in phosphate-poor surface waters of the North Atlantic subtropical gyre. Furthermore, it seems that their phosphate uptake may counter-intuitively be lower in more productive tropical waters, as if their cellular demand for phosphate decreases there. By flow sorting (33)P-phosphate-pulsed (32)P-phosphate-chased cells, we demonstrate that both Prochlorococcus and SAR11 cells exploit an extracellular buffer of labile phosphate up to 5-40 times larger than the amount of phosphate required to replicate their chromosomes. Mathematical modelling is shown to support this conclusion. The fuller the buffer the slower the cellular uptake of phosphate, to the point that in phosphate-replete tropical waters, cells can saturate their buffer and their phosphate uptake becomes marginal. Hence, buffer stocking is a generic, growth-securing adaptation for SAR11 and Prochlorococcus bacteria, which lack internal reserves to reduce their dependency on bioavailable ambient phosphate.

No MeSH data available.