title: Dominant oceanic bacteria secure phosphate using a large extracellular buffer.
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.
authors.affiliation: National Oceanography Centre, Ocean Biogeochemistry &Ecosystems Research Group, European Way, Southampton SO14 3ZH, UK.
authors.forename: Mikhail V
authors.initials: MV
authors.lastname: Zubkov
authors.affiliation: National Oceanography Centre, Ocean Biogeochemistry &Ecosystems Research Group, European Way, Southampton SO14 3ZH, UK.
authors.forename: Adrian P
authors.initials: AP
authors.lastname: Martin
authors.affiliation: National Oceanography Centre, Ocean Biogeochemistry &Ecosystems Research Group, European Way, Southampton SO14 3ZH, UK.
authors.forename: Manuela
authors.initials: M
authors.lastname: Hartmann
authors.affiliation: School of Life Sciences, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
authors.forename: Carolina
authors.initials: C
authors.lastname: Grob
authors.affiliation: School of Life Sciences, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Scanlan
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D020561:Alphaproteobacteria / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D001267:Atlantic Ocean; D002021:Buffers; D002245:Carbon Dioxide / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism*; D010759:Phosphorus Isotopes; D010839:Phytoplankton; D048929:Prochlorococcus / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D002021:Buffers; D010710:Phosphates; D010759:Phosphorus Isotopes; D002245:Carbon Dioxide; D000255:Adenosine Triphosphate