The stress-responsive alternative sigma factor SigB of Bacillus subtilis and its relatives: an old friend with new functions
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2020-09-15
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Frontiers Media
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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 with phytopathogenic fungi (e.g., Fusarium verticillioides) and halts fungal growth to the
benefit of plant growth. In this article, we update and review literature on the different
regulatory networks that control the activation of SigB and the new roles that have been
described the recent years.
Para citar este articulo: Rodriguez Ayala F, Bartolini M and Grau R (2020) The Stress-Responsive Alternative Sigma Factor SigB of Bacillus subtilis and Its Relatives: An Old Friend With New Functions. Front. Microbiol. 11:1761. doi: 10.3389/fmicb.2020.01761
Para citar este articulo: Rodriguez Ayala F, Bartolini M and Grau R (2020) The Stress-Responsive Alternative Sigma Factor SigB of Bacillus subtilis and Its Relatives: An Old Friend With New Functions. Front. Microbiol. 11:1761. doi: 10.3389/fmicb.2020.01761
Palabras clave
Bacillus subtilis, Alternative Sigma Factors, SigB, General Stress Response, Biofilms, Biocontrol, Sporulation