Add time:08/01/2019         Source:sciencedirect.com

Microbial oxidation of antimonite [Sb(III)] to antimonate [Sb(V)] is a detoxification process which contributes to Sb(III) resistance. Antimonite oxidase AnoA is essential for Sb(III) oxidation, however, the regulation mechanism is still unknown. Recently, we found that the expressions of phosphate transporters were induced by Sb(III) using proteomics analysis in Agrobacterium tumefaciens GW4, thus, we predicted that the phosphate regulator PhoB may regulate bacterial Sb(III) oxidation and resistance. In this study, comprehensive analyses were performed and the results showed that (1) Genomic analysis revealed two phoB (named as phoB1 and phoB2) and one phoR gene in strain GW4; (2) Reporter gene assay showed that both phoB1 and phoB2 were induced in low phosphate condition (50 μM), but only phoB2 was induced by Sb(III); (3) Genes knock-out/complementation, Sb(III) oxidation and Sb(III) resistance tests showed that deletion of phoB2 significantly inhibited the expression of anoA and decreased bacterial Sb(III) oxidation efficiency and Sb(III) resistant. In contrast, deletion of phoB1 did not obviously affect anoA’s expression level and Sb(III) oxidation/resistance; (4) A putative Pho motif was predicted in several A. tumefaciens strains and electrophoretic mobility shift assay (EMSA) showed that PhoB2 could bind with the promoter sequence of anoA; (5) Site-directed mutagenesis and short fragment EMSA revealed the exact DNA binding sequence for the protein-DNA interaction. These results showed that PhoB2 positively regulates Sb(III) oxidation and PhoB2 is also associated with Sb(III) resistance. Such regulation mechanism may provide a great contribution for bacterial survival in the environment with Sb and for bioremediation application.

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