Chill Induction of the SigB-Dependent General Stress Response inBacillus subtilisand Its Contribution to Low-Temperature Adaptation

Abstract

A variety of environmental and metabolic cues trigger the transient activation of the alternative transcription factor SigB of Bacillus subtilis, which subsequently leads to the induction of more than 150 general stress genes. This general stress regulon provides nongrowing and nonsporulated cells with a multiple, nonspecific, and preemptive stress resistance. By a proteome approach we have detected the expression of the SigB regulon during continuous growth at low temperature (15°C). Using a combination of Western blot analysis and SigB-dependent reporter gene fusions, we provide evidence for high-level and persistent induction of the sigB operon and the SigB regulon, respectively, in cells continuously exposed to low temperatures. In contrast to all SigB-activating stimuli described thus far, induction by low temperatures does not depend on the positive regulatory protein RsbV or its regulatory phosphatases RsbU and RsbP, indicating the presence of an entirely new pathway for the activation of SigB by chill stress in B. subtilis. The physiological importance of the induction of the general stress response for the adaptation of B. subtilis to low temperatures is emphasized by the observation that growth of a sigB mutant is drastically impaired at 15°C. Inclusion of the compatible solute glycine betaine in the growth medium not only improved the growth of the wild-type strain but rescued the growth defect of the sigB mutant, indicating that the induction of the general stress regulon and the accumulation of glycine betaine are independent means by which B. subtilis cells cope with chill stress.

Defining the structure of the general stress regulon of Bacillus subtilis using targeted microarray analysis and random forest classification

“…For low-temperature growth, the cultures were grown in minimal medium at 37 uC to OD 540 0.1 and then the cultures were shifted to 15 uC (Brigulla et al, 2003). Afterwards, the cultures were sampled at OD 540 0.9 and 1.0.…”

“…In this work, the following B. subtilis strains were used: the wild-type strain 168 Marburg (trpC2) (Burkholder & Giles, 1947) and its isogenic mutant BSM29 (trpC2 sigB : : spec), which was constructed by insertion of a spectinomycinresistance cassette into sigB (Brigulla et al, 2003). The strains were precultured in LB medium, in the case of BSM29 supplemented with 50 mg spectinomycin ml 21 .…”

“…Notes to the figure: 1 butanol stress has not been specifically assigned; we assume that it is quite similar to ethanol stress and assigned it to the RsbU-dependent pathway. 2 Low-temperature growth does not depend on either the RsbU-or the RsbPsensing pathway (Brigulla et al, 2003). The signalling is also RsbV-independent, but its nature is currently not known, and is therefore not defined (ND).…”

“…The collection of SigBactivating stress conditions includes sudden environmental stresses such as heat, acid, ethanol, butanol and osmotic stress, Mn 2+ , nitric oxide (NO), sodium nitroprusside (SNP) and blue light; energy stresses such as starvation for glucose, phosphate and oxygen; inhibitors that collectively trigger a decrease in the ATP pool [azide, carbonyl cyanide m-chlorophenylhydrazone (CCCP), mycophenolic acid], addition of antibiotics such as vancomycin and bacitracin; as well as growth at extreme temperatures, both high and low (Hecker et al, 2007;Price, 2000Price, , 2002Price, , 2011. The increased expression of the SigB regulon provides B. subtilis cells with a non-specific, multiple stress resistance against a wide range of stresses (Gaidenko & Price, 1998 expression also contributes to growth and survival at low temperatures and during extended stationary phases (Brigulla et al, 2003;Méndez et al, 2004). Though there are several studies supporting the important role of this general stress regulon, a detailed study of the functions of individual regulon members is required to comprehensively understand the role of the regulon itself in cellular stress management.…”

“…expression also contributes to growth and survival at low temperatures and during extended stationary phases (Brigulla et al, 2003; Méndez et al, 2004). Though there are several studies supporting the important role of this general stress regulon, a detailed study of the functions of individual regulon members is required to comprehensively understand the role of the regulon itself in cellular stress management.…”