The Stress-Responsive Alternative Sigma Factor SigB of Bacillus subtilis and Its Relatives: An Old Friend With New Functions

Abstract

Alternative sigma factors have led the core RNA polymerase (RNAP) to recognize different sets of promoters to those recognized by the housekeeping sigma A-directed RNAP. This change in RNAP promoter selectivity allows a rapid and flexible reformulation of the genetic program to face environmental and metabolic stimuli that could compromise bacterial fitness. The model bacterium Bacillus subtilis constitutes a matchless living system in the study of the role of alternative sigma factors in gene regulation and physiology. SigB from B. subtilis was the first alternative sigma factor described in bacteria. Studies of SigB during the last 40 years have shown that it controls a genetic universe of more than 150 genes playing crucial roles in stress response, adaption, and survival. Activation of SigB relies on three separate pathways that specifically respond to energy, environmental, and low temperature stresses. SigB homologs, present in other Gram-positive bacteria, also play important roles in virulence against mammals. Interestingly, during recent years, other unexpected B. subtilis responses were found to be controlled by SigB. In particular, SigB controls the efficiencies of spore and biofilm formation, two important features that play critical roles in adaptation and survival in planktonic and sessile B. subtilis communities. In B. subtilis, SigB induces the expression of the Spo0E aspartyl-phosphatase, which is responsible for the blockage of sporulation initiation. The upregulated activity of Spo0E connects the two predominant adaptive pathways (i.e., sporulation and stress response) present in B. subtilis. In addition, the RsbP serine-phosphatase, belonging to the energy stress arm of the SigB regulatory cascade, controls the expression of the key transcription factor SinR to decide whether cells residing in the biofilm remain in and maintain biofilm growth or scape to colonize new niches through biofilm dispersal. SigB also intervenes in the recognition of and response to surrounding microorganisms, a new SigB role that could have an agronomic impact. SigB is induced when B. subtilis is confronted

STAS Domain Only Proteins in Bacterial Gene Regulation

“…Partner-switching mechanisms utilizing SDoPs were originally described in B. subtilis , as a regulatory system to control the availability of sigma factors in response to environmental stress ( Losick and Stragier, 1992 ; Kang et al., 1996 ; Rodriguez Ayala et al., 2020 ). In addition to the control of sigma factors in B. subtilis , these SDoPs have been shown to regulate survival of L. monocytogenes inside the host and contribute to the virulence of this pathogen ( Chaturongakul and Boor, 2004 ).…”

“…Perhaps the best studied example of SDoPs in bacteria is in the regulation of sporulation in B. subtilis ( Figure 1 ). Specifically, these proteins regulate gene expression by indirectly affecting the ability of the alternative sigma factor, σ B , to bind the core RNA polymerase ( Dufour and Haldenwang, 1994 ; Rodriguez Ayala et al., 2020 ). Generally, these systems can be described as phosphorylation-dependent partner-switching regulatory systems involving anti-sigma factors/serine kinases, serine-threonine phosphatases, and anti-sigma antagonists ( Rodriguez Ayala et al., 2020 ).…”

“…Specifically, these proteins regulate gene expression by indirectly affecting the ability of the alternative sigma factor, σ B , to bind the core RNA polymerase ( Dufour and Haldenwang, 1994 ; Rodriguez Ayala et al., 2020 ). Generally, these systems can be described as phosphorylation-dependent partner-switching regulatory systems involving anti-sigma factors/serine kinases, serine-threonine phosphatases, and anti-sigma antagonists ( Rodriguez Ayala et al., 2020 ). The Regulation of σ B (Rsb) system is an example of such partner-switching regulatory systems involved in the rapid initiation of transcription of more than 150 general stress proteins following exposure to environmental stress in B. subtilis ( Haldenwang and Losick, 1979 ; Binnie et al., 1986 ; Hecker et al., 2007 ; Losick and Pero, 2018 ).…”

“…RsbW also has serine kinase activity which phosphorylates RsbV, such that when the input phosphatase (triggered by environmental/energy stress) is no longer active, RsbV remains phosphorylated. RsbW then dissociates from phosphorylated RsbV, allowing RsbW to sequester σ B until another environmental stress event is encountered ( Figure 1 ) ( Benson and Haldenwang, 1993 ; Alper et al., 1996 ; Kang et al., 1996 ; Yang et al., 1996 ; Rodriguez Ayala et al., 2020 ).…”

The Transcriptional Regulatory Network of Corynebacterium pseudotuberculosis

“…Both sigA and sigB were previously associated with virulence in other bacteria; SigA can be specifically required for the expression of virulence genes in M. tuberculosis [131,137]. SigB controls the expression of many genes involved in the virulence of pathogens, such as biofilm formation, cellular differentiation, pathogenesis, stress resistance and sporulation in several bacteria [131,138]. Pacheco et al assessed the role of SigE in C. pseudotuberculosis using a sigE-mutant strain under different stress conditions, including acid stress.…”