Cysteine-mediated reductive dissolution of poorly crystalline iron(III) oxides by Geobacter sulfurreducens

The reductive dissolution. of poorly crystalline ferric oxides, in the presence of cysteine was, investigated to evaluate the potential of cysteine,as-a possible electron carrier to stimulate the reduction of. iron(III) oxides by Geobacter sulfurreducens. The extent and rate of biotic and abiotic reduction of iron(III) oxides in the presence of cysteine at-various concentrations I were. compared. Iron(III) oxides were reduced abiotically by cysteine. The initial rate and extent of iron(III) oxide, reduction 1. we. re correlated linearly with the cysieine concentration ranging from 0 to 6 mM. Also, addition of 0.5-2 mM cysteine significantly stimulated the rate and the,extent of iron,(Ill) oxides reduction in cultures of G.sulfurreducens. The cysteine concentration decreased Jm accordance with,the increase of Fe(II), concentration and reached a nearly constant residual concentration. Cysteine depletion followed first-order kinetics and increased linearly with the cysteine concentration. An 8- to 11-fold increase in the extent of irbn(III) oxide reduction relative to the abiotic system was observed. Comparison of sorbed and dissolved Fe(II) concentrations between cultures amended with. cysteine and with other organic, chelators showed that solubilization is not the main factor in cysteine-stimulated Fe(III) reduction. Addition of enhanced the extent of iron(III)-oxide reduction, concomitant with the increase of the regenerated. cysteineconcentration and support the hypothesis that cysteine could serve as an electron carrier to transfer electrons from G. sulfurreducens to poorly crystalline iron(Ill) oxides.