Gene function and expression regulation of RuvRCAB in bacterial Cr(VI), As(III), Sb(III), and Cd(II) resistance.

Alishewanella sp. WH16-1 is a heavy metal-resistant bacterium. Previously, a putative YebC family regulator gene, designated ruvR, was associated with Cr(VI) resistance. In this study, comprehensive analyses were performed to study the role of ruvR and its adjunct putative DNA repairing genes, ruvCAB, in the heavy metal resistance of Alishewanella sp. WH16-1. RT-PCR analysis showed that ruvR is cotranscribed with ruvCAB. Gene mutation and complementation experiments indicated that ruvRCAB contributes to Cr(VI), As(III), Sb(III), and Cd(II) resistance in vivo. Random amplification of polymorphic DNA-PCR revealed that ruvCAB is associated with DNA repair mediated by these metals, and the presence of the metals in the cells was confirmed by elemental mapping and energy-dispersive X-ray spectrograph analysis. In addition, qRT-PCR, reporter gene assay, and in vivo and in vitro protein-DNA interaction experiments indicated that RuvR positively regulates the transcription of ruvCAB and is induced by Cr(VI). Finally, site-directed mutagenesis demonstrated that Asp103 is essential for the DNA binding ability of RuvR. The above results suggest that RuvR is involved in Cr(VI) resistance and resistance to other metals and that RuvR positively regulates the expression of ruvCAB. Based on our study and literatures, a model of RuvRCAB detailing bacterial heavy metal resistance is proposed. The RuvRCAB system plays an important role in the ability of Alishewanella sp. WH16-1 to survive in environments with heavy metals.