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

Abstract

Previously, the expression of arsenite [As(III)] oxidase genes aioBA 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 aioXSR genes are absent in some As(III)-oxidizing bacterial genomes, such as in Halomonas sp. HAL1. In this study, transposon mutagenesis and gene knock-out mutation were performed, and two mutants, HAL1-phoR931 and HAL1-▵phoB, were obtained in strain HAL1. The phoR and phoB 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 phoBR complementation strain HAL1-▵phoB-C reversed the mutants' null phenotypes back to wild type status. Meanwhile, lacZ reporter fusions using pCM-lacZ showed that the expression of phoBR and aioBA were both induced by As(III) but were not induced in HAL1-phoR931 and HAL1-▵phoB. Using 15 consensus Pho box sequences, a putative Pho box was found in the aioBA regulation region. PhoB was able to bind to the putative Pho box in vivo (bacterial one-hybrid detection) and in vitro (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 aioBA in Halomonas sp. HAL1 under low Pi condition. The new regulation model further implies the close metabolic connection between As and Pi.

Phosphate starvation response controls genes required to synthesize the phosphate analog arsenate

“…For example, As III oxidation in Halomonas sp. HAL‐1 is controlled by PhoRB in low Pi media, although apparently by some other regulatory system when the cells are grown in high Pi media (Chen et al ., ). Regardless of Pi level however, As III is required for aioBA induction in HAL‐1 under all conditions, demonstrating the constant regulatory linkage between As III and aioBA expression.…”

“…However, these experiments also used CDM medium and gene expression was assayed after 24 h, a period in which the cells would have reduced or indeed exhausted media Pi, leading to the induction of the PSR and the aio genes. Of particular importance in this regard, other As III oxidizing microorganisms lack the aioXSR genes (Chen et al, 2015), clearly implying some other regulatory system is in place. For example, As III oxidation in Halomonas sp.…”

Metabolic response of Agrobacterium tumefaciens 5A to arsenite

“…This oxidase is regulated by a three component signal transduction system AioXSR and RpoN (Kashyap et al, 2006;Koechler et al, 2010;Liu et al, 2012). In addition, elements of the phosphate stress response (PhoRB) are varyingly involved depending on the organism (Kang, Heinemann, et al, 2012;Chen et al, 2015).…”

Complete genome sequencing and comparative genomic analyses of Bacillus sp. S3, a novel hyper Sb(III)-oxidizing bacterium

“…The phosphate (Pi) related genes, such as phoB, pstS, and phoR, were also identified in Bacillus sp. S3, which have been proved to be coregulated with As(III) oxidation and could be induced by Sb(III) in previous report [44].…”