Abstract
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 H2O2 content and H2O2 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 H2O2 resistance. Furthermore, linear correlations were observed between cellular H2O2 and Sb(V) content in vivo and chemical H2O2 and Sb(V) content in vitro (R2 = 0.93 and 0.94, respectively). These results indicate that besides the biotic factors, the cellular H2O2 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 H2O2) and biotic (AnoA and AioAB) factors and Sb(III) oxidation process consumes cellular H2O2 which contributes to microbial detoxification of both Sb(III) and cellular H2O2.
Highlights
Antimony (Sb) is an element belonging to Group 15 of the Periodic Table and behaves similar to arsenic (As)
The catalase KatA is responsible for cellular H2O2 consumption[27], we proposed that the high efficient Sb(III) oxidation in strain GW4-ΔkatA might be associated with the cellular H2O2 content
The results indicated the following: i) The generation of cellular H2O2 was induced by Sb(III), ii) The cellular H2O2 content was consistent with the transcription level of genes associated with abiotic Sb(III) oxidation, and iii) The content of H2O2 was proportional to the bacterial Sb(III) oxidation efficiency
Summary
Antimony (Sb) is an element belonging to Group 15 of the Periodic Table and behaves similar to arsenic (As). Compared with A. tumefaciens 5A17, strain GW4 has considerably higher Sb(III) resistance and Sb(III) oxidation efficiency[18]. Deletion of each gene only partially influenced the Sb(III) oxidation efficiency of A. tumefaciens strains, indicating other unknown mechanisms. The aberrant electron flow under stress conditions from the electron transport chain or cellular redox enzymes to O2 results in the production of reactive oxygen species (ROS)[23]. We deleted the catalase gene katA in A. tumefaciens GW4 and observed that the Sb(III) oxidation efficiency of the mutant strain was significantly increased, and the phenotype of the complementary strain was recovered[16]. We proposed that the increased Sb(III) oxidation efficiency in the mutant strain might reflect the accumulation of H2O2 in bacterial cells. There is no direct evidence of a correlation between H2O2 and Sb(III) oxidation
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