AUTHOR=Chen Fang , Cao Yajing , Wei Sha , Li Yanzhi , Li Xiangyang , Wang Qian , Wang Gejiao 

TITLE=Regulation of arsenite oxidation by the phosphate two-component system PhoBR in Halomonas sp. HAL1

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.00923

DOI=10.3389/fmicb.2015.00923

ISSN=1664-302X

ABSTRACT=<p>Previously, the expression of arsenite [As(III)] oxidase genes <italic>aioBA</italic> was reported to be regulated by a three-component regulatory system, AioXSR, in a number of As(III)-oxidizing bacterial strains. However, the regulation mechanism is still unknown when <italic>aioXSR</italic> genes are absent in some As(III)-oxidizing bacterial genomes, such as in <italic>Halomonas</italic> sp. HAL1. In this study, transposon mutagenesis and gene knock-out mutation were performed, and two mutants, HAL1-<italic>phoR</italic><sub>931</sub> and HAL1-▵<italic>phoB</italic>, were obtained in strain HAL1. The <italic>phoR</italic> and <italic>phoB</italic> constitute a two-component system which is responsible for phosphate (Pi) acquisition and assimilation. Both of the mutants showed negative As(III)-oxidation phenotypes in low Pi condition (0.1 mM) but not under normal Pi condition (1 mM). The <italic>phoBR</italic> complementation strain HAL1-▵<italic>phoB</italic>-C reversed the mutants' null phenotypes back to wild type status. Meanwhile, <italic>lacZ</italic> reporter fusions using pCM-<italic>lacZ</italic> showed that the expression of <italic>phoBR</italic> and <italic>aioBA</italic> were both induced by As(III) but were not induced in HAL1-<italic>phoR</italic><sub>931</sub> and HAL1-▵<italic>phoB</italic>. Using 15 consensus Pho box sequences, a putative Pho box was found in the <italic>aioBA</italic> regulation region. PhoB was able to bind to the putative Pho box <italic>in vivo</italic> (bacterial one-hybrid detection) and <italic>in vitro</italic> (electrophoretic mobility gel shift assay), and an 18-bp binding sequence containing nine conserved bases were determined. This study provided the evidence that PhoBR regulates the expression of <italic>aioBA</italic> in <italic>Halomonas</italic> sp. HAL1 under low Pi condition. The new regulation model further implies the close metabolic connection between As and Pi.</p>