Regulation of Bacillus subtilis bacillithiol biosynthesis operons by Spx

Abstract

Bacillithiol is the major low molecular mass thiol produced by many firmicutes bacteria, including the model organism Bacillus subtilis and pathogens such as Bacillus anthracis and Staphylococcus aureus. We have previously shown that four genes (bshA, bshB1, bshB2 and bshC) are involved in bacillithiol biosynthesis. Here, we report that these four genes are encoded within three, unlinked operons all expressed from canonical s A -dependent promoters as determined by 59RACE (rapid amplification of cDNA ends). The bshA and bshB1 genes are embedded within a seven-gene operon additionally including mgsA, encoding methylglyoxal synthase, and the essential genes cca and birA, encoding tRNA nucleotidyltransferase (CCA transferase) and biotin-protein ligase, respectively. The bshB2 gene is co-transcribed with unknown function genes, while bshC is expressed both as part of a two-gene operon (with the upstream putative pantothenate biosynthesis gene ylbQ) and from its own promoter. All three operons are expressed at a reduced level in an spx null mutant, consistent with a direct role of Spx as a transcriptional activator for these operons, and all three operons are induced by the thiol oxidant diamide. In contrast with other Spx-regulated genes characterized to date, the effects of Spx on basal expression and diamide-stimulated expression appear to be independent of Cys10 in the redox centre of Spx. Consistent with the role of Spx as an activator of bacillithiol biosynthetic genes, cellular levels of bacillithiol are reduced several-fold in an spx null mutant.

Transcription of Oxidative Stress Genes Is Directly Activated by SpxA1 and, to a Lesser Extent, by SpxA2 in Streptococcus mutans

“…Mounting evidence indicates that transcriptional regulation by Spx is critical for the ability of low-GC Gram-positive bacteria to cope with oxidative stress (9,11,12,15,16,22,26,(33)(34)(35)(36). However, proof of direct regulation by Spx in bacteria other than B. subtilis has been limited to the nox gene of S. mutans (26).…”

Importance of Bacillithiol in the Oxidative Stress Response of Staphylococcus aureus

“…One of the possible signals for bsh genes is probably connected to thiol stress, as diamide, which oxidizes thiols and decreases reduced thiol levels, increases expression of both bshA and bshC in the wild type (see Table S1 in the supplemental material). SpxA, which has been connected to both the diamide stress response (55) and the regulation of BSH synthesis (56) in B. subtilis, is upregulated in cells treated with diamide and may be the link connecting the disparate operons.…”

Critical Minireview: The Fate of tRNA^Cysduring Oxidative Stress in <em>Bacillus subtilis</em>

“…The last step of BSH biosynthesis is achieved by coupling cysteine to GlcN-Mal, and is catalyzed by BshC (D-glucosaminyl L-malate cysteine ligase) [9,10]. BshA and BshC are essential in bacillithiol biosynthesis, while, in the absence of BshB1, bacillithiol production is reduced by up to 50%, indicative of the reduced activity of BshB2 [9,10]. The genes bshA and bshB1, whose products are involved in the first two steps of bacillithiol biosynthesis (Figure 1), are encoded in the same operon [9,10].…”

“…BshA and BshC are essential in bacillithiol biosynthesis, while, in the absence of BshB1, bacillithiol production is reduced by up to 50%, indicative of the reduced activity of BshB2 [9,10]. The genes bshA and bshB1, whose products are involved in the first two steps of bacillithiol biosynthesis (Figure 1), are encoded in the same operon [9,10]. The operon begins with a putative pyrophosphohydrolase (ypjD), a dihydrodipicolinate reductase (dapB), and methylglyoxal synthase (mgsA).…”