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Effects of phosphorus starvation versus limitation on the marine cyanobacterium P rochlorococcus MED4 I : uptake physiology
Author(s) -
Krumhardt Kristen M.,
Callnan Kate,
RoacheJohnson Kathryn,
Swett Tammy,
Robinson Daniela,
Reistetter Emily Nahas,
Saunders Jaclyn K.,
Rocap Gabrielle,
Moore Lisa R.
Publication year - 2013
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/1462-2920.12079
Subject(s) - biology , acclimatization , cyanobacteria , phosphorus , phototroph , phosphatase , biochemistry , enzyme , michaelis–menten kinetics , kinetics , biophysics , photosynthesis , botany , enzyme assay , bacteria , chemistry , genetics , physics , organic chemistry , quantum mechanics
Summary Recent measurements of natural populations of the marine cyanobacterium P rochlorococcus indicate this numerically dominant phototroph assimilates phosphorus ( P ) at significant rates in P ‐limited oceanic regions. To better understand uptake capabilities of P rochlorococcus under different P stress conditions, uptake kinetic experiments were performed on P rochlorococcus MED4 grown in P ‐limited chemostats and batch cultures. Our results indicate that MED4 has a small cell‐specific V max but a high specific affinity (α P ) 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 V max and α P for both inorganic and organic P ( PO 4 and ATP ). The Michaelis–Menten constant, K M , for PO 4 remained constant under different P stress conditions, whereas the K M for ATP was higher when cells were stressed for PO 4 , pointing to additional processes involved in uptake of ATP . MED4 cleaves the PO 4 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.