The reduction of arsenate to arsenite by an Anabaena‐bacteria assemblage isolated from the Waikato River

Abstract An Anabaena oscillaroides‐ bacteria assemblage, isolated from the arsenic‐rich Waikato River, was able to take up and reduce arsenate to arsenite. The assemblage growing in continuous culture with cyanophyte and bacterial densities of 4 × 10 5 and 6 × 10 5 cells ml ‐1 respectively, could reduce arsenate to arsenite at a rate of 12 ng As 10 6 cells ‐1 d ‐1 . The assemblage bacteria were separated from the A. oscillaroides filaments and found to be capable of arsenate reduction to arsenite. These results provide a possible explanation for previously unexplained changes in arsenic speciation in the Waikato River, from the thermodynamically favoured arsenate to arsenite.