title: Effects of phosphorus starvation versus limitation on the marine cyanobacterium Prochlorococcus MED4 I: uptake physiology.
abstract: Recent measurements of natural populations of the marine cyanobacterium Prochlorococcus indicate this numerically dominant phototroph assimilates phosphorus (P) at significant rates in P-limited oceanic regions. To better understand uptake capabilities of Prochlorococcus under different P stress conditions, uptake kinetic experiments were performed on Prochlorococcus MED4 grown in P-limited chemostats and batch cultures. Our results indicate that MED4 has a small cell-specific Vmax but a high specific affinity (αP ) for P, making it competitive with other marine cyanobacteria at low P concentrations. Additionally, MED4 regulates its uptake kinetics in response to P stress by significantly increasing Vmax and αP for both inorganic and organic P (PO4 and ATP). The Michaelis-Menten constant, KM , for PO4 remained constant under different P stress conditions, whereas the KM for ATP was higher when cells were stressed for PO4 , pointing to additional processes involved in uptake of ATP. MED4 cleaves the PO4 moieties from ATP, likely with a 5'-nucleotidase-like enzyme rather than alkaline phosphatase. MED4 exhibited distinct physiological differences between cells under steady-state P limitation versus those transitioning from P-replete to P-starved conditions. Thus, MED4 employs a variety of strategies to deal with changing P sources in the oceans and displays complexity in P stress acclimation and regulatory mechanisms.
authors: Department of Biological Sciences, University of Southern Maine, Portland, ME, 04104, USA.
authors: Kristen M
authors: KM
authors: Krumhardt
authors: Kate
authors: K
authors: Callnan
authors: Kathryn
authors: K
authors: Roache-Johnson
authors: Tammy
authors: T
authors: Swett
authors: Daniela
authors: D
authors: Robinson
authors: Emily Nahas
authors: EN
authors: Reistetter
authors: Jaclyn K
authors: JK
authors: Saunders
authors: Gabrielle
authors: G
authors: Rocap
authors: Lisa R
authors: LR
authors: Moore
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D009792:Oceans and Seas; D010758:Phosphorus / Q000378:metabolism*; D048929:Prochlorococcus / Q000378:metabolism / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D010758:Phosphorus