Na+-stimulated phosphate uptake system in Synechocystis sp. PCC 6803 with Pst1 as a main transporter

Growth rates of the two mutants and wild type were similar either under phosphate-sufficient or deficient condition. The Km for phosphate uptake was 6.09 μM in wild type and this was reduced to 0.13 μM in ΔPst1 cells and 5.16 μM in the ΔPst2 strain. The Vmax values of 2.48, 0.22, and 2.17 μmol ？ (min ？ mg of chlorophyll a)-1 were obtained for wild type, the ΔPst1 and ΔPst2 strains, respectively. A monophasic phosphate uptake was observed in wild-type cells. The uptake of phosphate was energy and pH-dependent with a broad pH optimum between pH 7-10. Osmolality imposed by NaCl stimulated phosphate uptake whereas that imposed by sorbitol decreased uptake, suggesting stimulation of uptake was dependent upon ionic effects.The data demonstrate that Pst2 system of Synechocystis has higher affinity toward phosphate with lower Vmax than Pst1 system. The Pst1 system had similar Km and Vmax values to those of the wild type suggesting that Pst1 is the main phosphate transporter in Synechocystis sp. PCC 6803. The Km of Pst1 of Synechocystis is closer to that of Pit system than to that of the Pst system of E. coli, suggesting that Synechocystis Pst1 is rather a medium/low affinity transporter whereas Pst2 is a high affinity transporter.Phosphorus is an essential mineral nutrient for all organisms, for example, for the biosynthesis of nucleotides such as ATP as well as DNA and RNA, and for the functional regulation of proteins by phosphorylation. However, inorganic phosphate (Pi), the only form of phosphorus that can be directly utilized by cells, is often limiting in natural environments where it is frequently present at nanomolar levels [1]. In response to Pi limitation, the expression of genes for proteins that participate in the uptake and/or in the scavenging of Pi is induced under the control of a Pi-specific two-component system [2-5]. In Escherichia coli, Pi uptake is carried out by two kinetically distinct systems: the high affinity phosphate-specific transport (Pst) syst