An Lrp-type transcriptional regulator controls expression of the Bacillus subtilis chromate transporter

Abstract

The Bacillus subtilis strain 168 genome contains the chr3N-chr3C genes encoding the Chr3N/Chr3C protein pair of the chromate ion transporter (CHR) superfamily. Chr3N/Chr3C confers chromate resistance in Escherichia coli only when both proteins are expressed. Upstream of chr3N is the chrS gene encoding ChrS, a protein with homology to the Lrp/AsnC family of transcriptional regulators. When the chrS-chr3N-chr3C gene cluster was transferred to E. coli, a diminished level of chromate resistance was observed, as compared with E. coli transformants bearing only the chromate resistance genes, which displayed full resistance. These data suggested that the chrS gene product acts as negative regulator. RT-PCR assays demonstrated that expression of chrS diminishes transcription of the chromate resistance genes in E. coli, and that this repression was overcome by chromate. Electrophoretic mobility shift assays showed that purified ChrS protein specifically binds to the 5' region of chrS. These results indicate that the chr gene cluster forms an operon regulated negatively by ChrS binding to its own gene's regulatory region, and positively by chromate ions. Sequence analysis revealed similar operons in many Bacillales strains, suggesting some adaptive advantage. This is the first example of a bacterial heavy-metal resistance system controlled by an Lrp-type transcriptional regulator.

Implantation of Bacillus pseudomycoides Chromate Transporter Increases Chromate Tolerance in Bacillus subtilis

“…B. subtilis is itself moderately Cr-tolerant as it tolerates time-limited exposure to Cr(VI) in sub-millimolar concentrations and can resume the growth after the concentration of the toxic metal decreases ( Garbisu et al, 1998 ). B. subtilis harbors an innate Cr efflux system in its genome, consisting of two SCHR chromate transporters ywrB ( chr3N ) and ywrA ( chr3C ), expression of which is regulated by a Cr-responsive Lrp-type regulator ChrS ( Díaz-Magaña et al, 2009 ; Aguilar-Barajas et al, 2013 ). In contrast, the Cr-resistant NCr1a strain likely harbors only chromosomally encoded putative LCHR chromate transporter ChrA with no regulator sequences detected in the close vicinity of its promoter region.…”

“…Our experimental hypothesis was that the Cr efflux pump of the NCr1a strain, ChrA, may be more effective than its PY79 counterpart, YwrBA. This seemed to be supported by the fact that the two efflux pumps belong to divergent families within the CHR superfamily, that their genetic determinants are differently organized in the genome, and their expression is dissimilarly regulated ( Díaz-Pérez et al, 2007 ; Aguilar-Barajas et al, 2013 ).…”

“…All chromate transporters typically possess multiple transmembrane segments (TMS). Very little is known about Cr efflux regulation, as only two subfamilies of LCHR family (LCHR2 and LCHR5) and one subfamily of SCHR (SCHR1) are known to express regulatory genes together with the chromate transporter ( Díaz-Pérez et al, 2007 ; Aguilar-Barajas et al, 2013 ). These regulatory genes differ in number as well as in mode of action across genera, species, or even individual strains ( Branco et al, 2008 ; Henne et al, 2009 ; He et al, 2010 ; Aguilar-Barajas et al, 2013 ; Klonowska et al, 2020 ).…”

Enhancement of precursor amino acid supplies for improving bacitracin production by activation of branched chain amino acid transporter BrnQ and deletion of its regulator gene lrp in Bacillus licheniformis

“…Moreover, the transcriptional levels of brnQ were enhanced in lrp deletion strain and reduced in lrp overexpression strains, and EMSA results confirmed that Lrp indirectly regulate BrnQ expression. Previously, Lrp has been demonstrated to be involved in the regulations of chromate transporter, chromosome condensation, sporulation and amino acid metabolism in B. subtilis [ 23 , [30] , [31] , [32] ]. Although it was reported that AzlB, a Lrp-like protein, could regulate the distribution of BCAAs in B. subtilis , this regulation mechanism has not been well studied [ 23 ].…”

Analysis of Haloferax mediterranei Lrp Transcriptional Regulator

“…mediterranei and incorporated into its cellular interior [30]. There is a previous assay about a bacterial heavy-metal resistance system controlled by an Lrp-type transcriptional regulator in Bacillus subtilis [56]. For this reason, why not think that these metals may be acting as ligands binding to the Lrp, inducing conformational changes in the structure that may affect the DNA binding by changing the DNA binding affinity?…”