Iron promoted reduction of chromate by dissimilatory iron-deducing bacteria

Chromate is a priority pollutant within the U.S. and many other countries, the hazard of which can be mitigated by reduction to the trivalent form of chromium. Here we elucidate the reduction of Cr(VI)to Cr(III)via a closely coupled, biotic-abiotic reductive pathway under iron-reducing conditions. Injection of chromate into stirred-flow reactors containing Shewanella alga strain BrY and iron (hydr)oxides of varying stabilities results in complete reduction to Cr(lll), The maximum sustainable Cr(VI) reduction rate was 5.5 mug Cr-VI.mg-cell(-1).h(-1) within ferric (hydr)oxide suspensions (surface area 10 m(2)). In iron limited systems (having HEPES as a buff er), iron was cycled suggesting it acts in a catalytic-type manner for the bacterial reduction of Cr(VI). Cry also reduced Cr(VI) directly; however, the rate of direct (enzymatic) reduction is considerably slower than by Fe(II)((aq)) and is inhibited within 20 h due to chromate toxicity. Thus, dissimilatory iron reduction may provide a primary pathway for the sequestration and detoxification of chromate in anaerobic soils and water.