Analysis of the expression and function of the sigmaB-dependent general stress regulon of Bacillus subtilis during slow growth.

Glucose-limited continuous cultures were used to analyze sigmaB activity at decreasing growth rates. Expression of the sigmaB-dependent genes gsiB and ctc started to increase at a growth rate of 0.2 h-1, and both genes were induced approximately fivefold at a growth rate of 0.1 h-1 as compared to expression at the maximal growth rate. However, maximal sigmaB activity was only reached when the growth stopped as a result of the exhaustion of the carbon and energy source glucose. During glucose-limited growth, increased expression of the general stress regulon at growth rates below 0.2 h-1 did not provide wild-type cells with a growth advantage over sigB mutants. Instead, expression of the stress regulon seems to constitute a significant burden during glucose-limited growth, resulting in a selective growth advantage of the sigB mutant as compared to the wild-type at a growth rate of 0.08 h-1.