Reduction of Fe(III), Cr(VI), U(VI), and Tc(VII) by Deinococcus radiodurans R1

Deinococcus radiodurans is an exceptionally radiation-resistant microorgani sm capable of surviving acute exposures to ionizing radiation doses of 15,0 00 Gy and previously described as having a strictly aerobic respiratory met abolism. Under strict anaerobic conditions, D. radiodurans R1 reduced Fe(II I)-nitrilotriacetic acid coupled to the oxidation of lactate to CO2 and ace tate but was unable to link this process to growth. D. radiodurans reduced the humic acid analog anthraquinone-2,6-disulfonate (AQDS) to its dihydroqu inone form, AH(2)DS. which subsequently transferred electrons to the Fe(III ) oxides hydrous ferric oxide and goethite via a previously described elect ron shuttle mechanism. D. radiodurans reduced the solid phase Fe(III) oxide s in the presence of either 0.1 mM AQDS or leonardite humic acids (2 mg ml( -1)) but not in their absence. D, radiodurans also reduced U(VI) and Tc(VII ) in the presence of AQDS. In contrast, Cr(VI) was directly reduced in anae robic cultures with lactate although the rate of reduction was higher in th e presence of AQDS. The results are the first evidence that D. radiodurans can reduce Fe(III) coupled to the oxidation of lactate or other organic com pounds. Also, D. radiodurans, in combination with humic acids or synthetic electron shuttle agents, can reduce U and Te and thus has potential applica tions for remediation of metal- and radionuclide-contaminated sites where i onizing radiation or other DNA-damaging agents may restrict the activity of more sensitive organisms.