Hyper-resistance to arsenate in the cyanobacterium Synechocystis sp. PCC 6803 is influenced by the differential kinetics of its pst-ABC transporters and external phosphate concentration exposure

Abstract

Phosphate transporters, which take up not only phosphate but also arsenate, have attracted attention for phosphorus (P) resource recovery from eutrophic environments and arsenic (As) removal from polluted areas by bioremediation. The cyanobacterium Synechocystis sp. PCC 6803 can grow in a higher ratio of arsenate (150 mM) to phosphate (0.2 mM) in comparison with plants and microalgae. Analysis of the As resistance of the Pst1 and Pst2 phosphate transporter deletion mutants (Δpst1 and Δpst2) showed that the Δpst1 strain is more sensitive to arsenate under P-replete conditions but more resistant under P-deplete conditions compared with Δpst2 cells and wild type. This pattern in sensitivity is attributed to the levels of initial As accumulation and pst gene expression. Moreover, the ratio of phosphate uptake to arsenate uptake rates at 10 μM was 7–10:1 in the wild type and the Δpst2 mutant, while that in Δpst1 and Δ pstS1 (phosphate-binding protein from the pst1 gene cluster), were about 1.5:1, suggesting a high selectivity of Pst1 for phosphate.