TABLE 2.

List of alternative sigma factors with structural similarity to B. subtilis SigB present in different Gram-positive bacteria.

SigB Orthologs
Module	Microorganism	Name	Functions	References
B. subtilis	B. subtilis	SigB	See Table 1
	B. licheniformis		General stress sigma factor	Brody et al., 2009
	B. coagulans, B. amyloliquefaciens, B. pumilus, B. clausii		Not reported	de Been et al., 2011
	Oceanobacillus iheyensis		Not reported	de Been et al., 2011
	Listeria monocytogenes, L. innocua		Activated in response to nutritional and environmental stresses.	Wiedmann et al., 1998; Chaturongakul et al., 2008; Toledo-Arana et al., 2009; van der Veen and Abee, 2010; Ondrusch and Kreft, 2011
			Responsible for swimming motility and invasiveness in the presence of blue light.
			Involved in the resistance of both planktonic cells and biofilms to the disinfectants benzalkonium chloride and peracetic acid in L. monocytogenes.
			Deletion of sigB attenuated virulence in L. monocytogenes
	L. welshimeri		Not reported	de Been et al., 2011
B. cereus	B. thuringiensis B. cereus B. anthracis B. weihenstephanensis	SigB	See Table 1	Fouet et al., 2000; van Schaik et al., 2004
S. coelicolor	S. coelicolor	SigF	sigF is needed for spore maturation	Cho et al., 2001; Bentley et al., 2002
		SigH	The sigH operon is controlled by environmental stress (heat, salt, ethanol) and developmental signals.
			A strain with a mutated sigH allele is reported to have some abnormalities in spore formation and to be slightly osmosensitive.
		SigB	sigB is induced by salt and plays a role in osmoprotection and erection of aerial mycelium
	S. avermitilis, S. griseus	SigB	Not reported	de Been et al., 2011
	Thermobifida fusca		Not reported	de Been et al., 2011
	Salinispora tropica, S. arenicola		Not reported	de Been et al., 2011
	Frankia alni, Frankia Ccl3, Frankia EAN1pec		Not reported	de Been et al., 2011
S. aureus		SigB	Regulate biosynthesis of staphyloxanthin, a key virulence factor for protecting S. aureus from host-oxidant killing in vivo	Wu et al., 1996; Giachino et al., 2001; Bischoff et al., 2004; Chen et al., 2016
			Its increased expression always is accompanied by enhanced biofilm formation
			Responsible for antibiotic resistance
Clostridium	C. difficile	SigB	Crucial role in adaptive strategies during gut infection	Kint et al., 2017, 2019
	C. thermocellum, C. cellulotycum, C. sticklandii, C. sordellii	SigB	Not reported
M. tuberculosis		SigF	Induced under a variety of stress conditions, most notably antibiotic stress, low oxygen tensions, nutrient depletion, oxidative stress, and during stationary-phase growth	DeMaio et al., 1996, 1997; Michele et al., 1999; Geiman et al., 2004
			Is involved in cell surface modification and virulence factor secretion
Synechocystis sp.		SigF	Mutant showed a severe defect in the induction of salt stress proteins	Bhaya et al., 1999; Huckauf et al., 2000
			Required for the biosynthesis of pili and that specific pilA genes