Abiotic and biotic factors responsible for antimonite oxidation in Agrobacterium tumefaciens GW4

Antimonite [Sb(III)]-oxidizing bacteria can transform the toxic Sb(III) into the less toxic antimonate [Sb(V)]. Recently, the cytoplasmic Sb(III)-oxidase AnoA and the periplasmic arsenite [As(III)] oxidase AioAB were shown to responsible for bacterial Sb(III) oxidation, however, disruption of each gene only partially decreased Sb(III) oxidation efficiency. This study showed that in Agrobacterium tumefaciens GW4, Sb(III) induced cellular H(2)O(2) content and H(2)O(2) degradation gene katA. Gene knock-out/complementation of katA, anoA, aioA and anoA/aioA and Sb(III) oxidation and growth experiments showed that katA, anoA and aioA were essential for Sb(III) oxidation and resistance and katA was also essential for H(2)O(2) resistance. Furthermore, linear correlations were observed between cellular H(2)O(2) and Sb(V) content in vivo and chemical H(2)O(2) and Sb(V) content in vitro (R(2) = 0.93 and 0.94, respectively). These results indicate that besides the biotic factors, the cellular H(2)O(2) induced by Sb(III) also catalyzes bacterial Sb(III) oxidation as an abiotic oxidant. The data reveal a novel mechanism that bacterial Sb(III) oxidation is associated with abiotic (cellular H(2)O(2)) and biotic (AnoA and AioAB) factors and Sb(III) oxidation process consumes cellular H(2)O(2) which contributes to microbial detoxification of both Sb(III) and cellular H(2)O(2).