Induction of the Spx regulon by cell wall stress reveals novel regulatory mechanisms in Bacillus subtilis

Abstract

The transcription factor Spx is the master regulator of the disulfide stress response in Bacillus subtilis. Intriguingly, the activation of Spx by diamide relies entirely on posttranslational regulatory events in spite of the complex transcriptional control of the spx gene. Here, we show that cell wall stress, but not membrane stress, also results in induction of the Spx regulon. Remarkably, two major differences were found regarding the mechanism of induction of Spx under cell wall stress in comparison to disulfide stress. First, transcriptional induction of the spx gene from a σ -dependent promoter is required for accumulation of Spx in response to cell wall stress. Second, activation of the Spx regulon during cell wall stress is not accompanied by oxidation of the Spx disulfide switch. Finally, we demonstrate that cells lacking Spx have increased sensitivity toward antibiotics inhibiting both early and late steps in peptidoglycan synthesis, suggesting that the Spx regulon plays an important adaptive role in the cell wall stress response. This study expands the functional role of the Spx regulon and reveals novel regulatory mechanisms that result in induction of Spx in B. subtilis.

Deciphering the essentiality and function of the anti‐σM factors in Bacillus subtilis

“…A 20 min. treatment time was chosen, since this was shown previously to be optimal for monitoring SigM‐dependent induction (Rojas‐Tapias and Helmann, ), B. Fold change of maximum SigM activity (monitored using the P M ‐ lux reporter) by vancomycin (left) and EDTA (right) in WT (HB17325) and mutants (P xylA ‐ sigA , HB23619; yhdK , HB20833; P xylA ‐ sigA yhdK , HB23937; P xylA ‐ sigA yhdL , HB23939).…”

YjbH Solubility Controls Spx in Staphylococcus aureus: Implication for MazEF Toxin-Antitoxin System Regulation

“…However, no other stress stimuli have been tested. At the post-transcriptional level, YjbH activity can be modulated by aggregation and/or through anti-adaptor proteins and/or phosphorylation following different stimuli, as shown in B. subtilis and other bacteria (Kirstein et al, 2007;Elsholz et al, 2011;Engman and von Wachenfeldt, 2015;Rojas-Tapias and Helmann, 2018). Our results show that in S. aureus, YjbH can also aggregate, however, the identification of YjbH anti-adaptors such as YirB in B. subtilis, or adaptor phosphorylation remains to be investigated.…”

“…As no correlation between transcription and Spx protein levels was observed, Spx post-transcriptional regulation was postulated. Indeed, Spx levels can be modulated by proteolysis through ClpXP, and Spx activity can be modulated by its redox state that differs upon different stimuli in B. subtilis (Rojas-Tapias and Helmann, 2018). We observed a stimuli dependent Spx protein aggregation that affected Spx activity, and could conceivably be responsible for downstream effects, such as regulation of MazEF TAS.…”

“…Moreover, it has recently been observed that depending on the stimuli, different regulatory events occur to increase and activate Spx (Rojas-Tapias and Helmann, 2018). While activation of Spx regulon under oxidative stress is accompanied by decreased proteolysis and decreased oxidation state of Spx itself, activation of Spx regulon under cell wall stress requires Spx transcriptional increase and Spx reduced state (Rojas-Tapias and Helmann, 2018).…”

“…Spx is a transcriptional factor, which interacts with the alpha−subunit of the RNA polymerase and induces transcription of many genes, including trfA (Jousselin et al, 2013). In B. subtilis it was shown that oxidation of Spx molecule leads to formation of intramolecular S-S bond between Cys10 and Cys13, that modulates the activity of Spx (Antelmann and Helmann, 2011;Rojas-Tapias and Helmann, 2018). These amino acid residues are conserved in S. aureus.…”