ARSENIC BIOTRANSFORMATION IN CYANOBACTERIUM Synechocystis sp PCC 6803 UNDER DIFFERENT PHOSPHATE REGIMES

To explore the role of phosphate (P) in arsenic biotransformation by cyanobacteria, arsenic uptake and biotransformation by Synechocystis sp. PCC6803 in the BG-11 cultures treated with arsenate were investigated under laboratory conditions. The treatments of 0-100 mu M arsenate [As(V)] promoted cell growth, except in P-deprived medium. However, cell growth was inhibited when initial phosphate decreased. The cells of cyanobacteria can accumulate arsenic up to 1189.10 mg kg(-1) DW, and detoxify by reduction, methylation, or excretion to the external. For the phosphate-excess medium, arsenate makes up >80% of the total cellular arsenic, while arsenite [As(III)] dominated (50-69%) in algal cells for non-phosphate-excess media. Methyl-arsenate [MMA(V)] and/or dimethyl-arsenate [DMA(V)] were detected in algal cells and in the medium at low levels. Arsenate inhibited phosphate uptake by this alga, which indicated the competition between arsenate and phosphate for cellular uptake. We propose that phosphate plays a critical role in arsenic metabolism of Synechocystis sp. PCC6803.