A symbiotic bacterium differentially influences arsenate absorption and transformation in Dunaliella salina under different phosphate regimes.

In this study, we investigated the effects of a symbiotic bacterium and phosphate (PO4(3-)) nutrition on the toxicity and metabolism of arsenate (As(V)) in Dunaliella salina. The bacterium was identified as Alteromonas macleodii based on analysis of its 16S rRNA gene sequence. When no As(V) was added, A. macleodii significantly enhanced the growth of D. salina, irrespective of PO4(3-) nutrition levels, but this effect was reversed after As(V)+PO4(3-) treatment (1.12mgL(-1)) for 3 days. Arsenic (As) absorption by the non-axenic D. salina was significantly higher than that by its axenic counterpart during incubation with 1.12mgL(-1) PO4(3-). However, when the culture was treated with 0.112mgL(-1) PO4(3-), As(V) reduction and its subsequent arsenite (As(III)) excretion by non-axenic D. salina were remarkably enhanced, which, in turn, contributed to lower As absorption in non-axenic algal cells from days 7 to 9. Moreover, dimethylarsinic acid was synthesized by D. salina alone, and the rates of its production and excretion were accelerated when the PO4(3-) concentration was 0.112mgL(-1). Our data demonstrate that A. macleodii strongly affected As toxicity, uptake, and speciation in D. salina, and these impacts were mediated by PO4(3-) in the cultures.