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. I
njection 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 (surfac
e 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)) a
nd is inhibited within 20 h due to chromate toxicity. Thus, dissimilatory i
ron reduction may provide a primary pathway for the sequestration and detox
ification of chromate in anaerobic soils and water.