Study on phosphate uptake of the marine cyanophyte Synechococcus sp. NIBB 1071 in relation to oligotrophic environments in the open ocean |
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Authors: | T Ikeya K Ohki M Takahashi Y Fujita |
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Institution: | (1) Department of Cell Biology, National Institute for Basic Biology, Okazaki, Aichi 444, Japan, JP;(2) Botany Department, Faculty of Science, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan, JP |
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Abstract: | Inorganic phosphate (Pi) uptake by the marine cyanophyte Synechococcus sp. NIBB 1071 was studied using cells grown in an artificial seawater medium. The phosphate uptake was markedly enhanced
in cells grown in the medium of low phosphate concentrations (phosphate-limited cells) than in cells grown in the phosphate-rich
medium (phosphate-replete cells). The diagnosis of kinetics of instantaneous phosphate-uptake showed that V
max of the former was more than two orders of magnitude greater than that of the latter, and the k
m of the former was about 1/20 of that of the latter. The enhancement of the phosphate uptake was completed after a 40-h incubation
of phosphate-replete cells in the phosphate-free medium. The activation was suppressed by chloramphenicol, an inhibitor of
protein synthesis. The uptake developed in phosphate-limited cells was energy dependent and susceptive to osmotic shock, which
suggests the involvement of a periplasmic phosphate-binding protein, analogous to that found in heterotrophic gram-negative
eubacterial cells. The relationship between phosphate quota and growth rate, together with the kinetical data for phosphate
uptake, predicted that ambient phosphate as low as 0.5 nM could support cell growth at a rate of one division per day. Results indicate that cells can grow rapidly even at phosphate
concentrations as low as nanomolar levels. A possible regulatory mechanism of phosphate uptake in marine Synechococcus spp. is discussed in relation to a wide distribution of this picophytoplankton in the ocean environment.
Received: 19 March 1997 / Accepted: 2 April 1997 |
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