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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.


Comparison of observations and model output of inorganic phosphate uptake during 33P-phosphate pulse and 32P-phosphate chase experiments.Observations (black circles) and model output (blue lines) of traced inorganic phosphate (33Pi and 32Pi) in cells during six pulse–chase experiments (top row of plots) at two contrasting sites: least productive waters of the gyre centre and more productive tropical waters. Seawater samples with bioassayed ambient 31Pi were pulsed with 0.8 or 2.4 nmol l−1 31Pi labelled with 0.05 nmol l−1 33Pi and chased after 1 h incubation with 80 or 800 nmol l−1 and 240 or 2,400 nmol l−1 of 31Pi labelled with 0.01 nmol l−1 32Pi. Note that observations and model output values are normalized to the maximum uptake measure (counts per minute per ml) in a time course in each experiment to lie between 0 and 100%. dil, dilution.
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f2: Comparison of observations and model output of inorganic phosphate uptake during 33P-phosphate pulse and 32P-phosphate chase experiments.Observations (black circles) and model output (blue lines) of traced inorganic phosphate (33Pi and 32Pi) in cells during six pulse–chase experiments (top row of plots) at two contrasting sites: least productive waters of the gyre centre and more productive tropical waters. Seawater samples with bioassayed ambient 31Pi were pulsed with 0.8 or 2.4 nmol l−1 31Pi labelled with 0.05 nmol l−1 33Pi and chased after 1 h incubation with 80 or 800 nmol l−1 and 240 or 2,400 nmol l−1 of 31Pi labelled with 0.01 nmol l−1 32Pi. Note that observations and model output values are normalized to the maximum uptake measure (counts per minute per ml) in a time course in each experiment to lie between 0 and 100%. dil, dilution.

Mentions: To find out how cells maintain their phosphate buffers, we carried out more complex experiments in which the 33P-phosphate pulse was chased with higher concentrations of phosphate, but this time the chase was labelled with a 32P-phosphate tracer (Fig. 2, top row). An example of our approach is as follows: a seawater sample was pulsed with 0.8 nmol phosphate per l labelled with 33P-phosphate. After incubation at in situ temperature in the dark for 1 h, a chase labelled with 32P-phosphate was added at a concentration of 80 or 800 nmol phosphate per l and the sample was incubated for a further 2 h. In control experiments, a sample pulsed with 0.8 nmol phosphate per l labelled with 33P-phosphate was chased with 32P-phosphate tracer addition (<0.01 nmol phosphate per l). Microbial uptake of 33P and 32P tracers was followed during the pulse and chase phases of the incubation.


Dominant oceanic bacteria secure phosphate using a large extracellular buffer.

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

Comparison of observations and model output of inorganic phosphate uptake during 33P-phosphate pulse and 32P-phosphate chase experiments.Observations (black circles) and model output (blue lines) of traced inorganic phosphate (33Pi and 32Pi) in cells during six pulse–chase experiments (top row of plots) at two contrasting sites: least productive waters of the gyre centre and more productive tropical waters. Seawater samples with bioassayed ambient 31Pi were pulsed with 0.8 or 2.4 nmol l−1 31Pi labelled with 0.05 nmol l−1 33Pi and chased after 1 h incubation with 80 or 800 nmol l−1 and 240 or 2,400 nmol l−1 of 31Pi labelled with 0.01 nmol l−1 32Pi. Note that observations and model output values are normalized to the maximum uptake measure (counts per minute per ml) in a time course in each experiment to lie between 0 and 100%. dil, dilution.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Comparison of observations and model output of inorganic phosphate uptake during 33P-phosphate pulse and 32P-phosphate chase experiments.Observations (black circles) and model output (blue lines) of traced inorganic phosphate (33Pi and 32Pi) in cells during six pulse–chase experiments (top row of plots) at two contrasting sites: least productive waters of the gyre centre and more productive tropical waters. Seawater samples with bioassayed ambient 31Pi were pulsed with 0.8 or 2.4 nmol l−1 31Pi labelled with 0.05 nmol l−1 33Pi and chased after 1 h incubation with 80 or 800 nmol l−1 and 240 or 2,400 nmol l−1 of 31Pi labelled with 0.01 nmol l−1 32Pi. Note that observations and model output values are normalized to the maximum uptake measure (counts per minute per ml) in a time course in each experiment to lie between 0 and 100%. dil, dilution.
Mentions: To find out how cells maintain their phosphate buffers, we carried out more complex experiments in which the 33P-phosphate pulse was chased with higher concentrations of phosphate, but this time the chase was labelled with a 32P-phosphate tracer (Fig. 2, top row). An example of our approach is as follows: a seawater sample was pulsed with 0.8 nmol phosphate per l labelled with 33P-phosphate. After incubation at in situ temperature in the dark for 1 h, a chase labelled with 32P-phosphate was added at a concentration of 80 or 800 nmol phosphate per l and the sample was incubated for a further 2 h. In control experiments, a sample pulsed with 0.8 nmol phosphate per l labelled with 33P-phosphate was chased with 32P-phosphate tracer addition (<0.01 nmol phosphate per l). Microbial uptake of 33P and 32P tracers was followed during the pulse and chase phases of the incubation.

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.