Growth medium-independent genetic competence mutants of Bacillus subtilis

Abstract

The development of competence in Bacilus subtilis is normally dependent on the growth medium. Expression of late competence genes occurs in glucose-minimal salts-based media but not in complex media. Expression is also inhibited when glutamind is added to competence medium and when glycerol is substituted for glucose. Mutations have been identified in two regulatory loci, mecA and mecB, which render competence development independent of these variables. Although in mec mutants the expression of late competence genes, as weil as of competence itself, occurred in all media tested, this expression was still growth stage regulated. Thus at least some forms of medium-dependent and growth stage-specific regulation are genetically separable. One of the mecB mutations (mecB31) conferred oligosporogenicity. The mecB mutations were tightiy linked by transformation to rif, lpm, and std markers and were located between nif-2103 and cysA14. The mecA42 mutant was linked by transduction to argC4.

The regulation of competence transcription factor synthesis constitutes a critical control point in the regulation of competence in Bacillus subtilis

“…Figure 1A shows that MecA deficiency causes a three-to fourfold increase in comK expression. comG-lacZ expression is very low in complex media but is derepressed in a mecA loss-of-function mutant background (10). Similarly, comK-lacZ expression was not observed in complex medium (LB) in the mecA + background, but elevated expression occurred in the mecA mutant.…”

“…The negative effect of MecA on late competence gene expression (10,27,28) can therefore be most simply explained as an effect on comK expression, preventing the autoregulatory buildup of ComK. The MecA deficiency relieves the nutritional requirements for competence and for comK expression.…”

“…The mutational inactivation of mecA increases the expression of late competence genes (10,28). In addition, overexpression of MecA results in a severe decrease in late competence gene expression (28).…”

“…The synthesis of the late gene products is negatively regulated by the products of mecA and mecB (10,27,28,35,44). It has been postulated that the Mec proteins serve to sequester or otherwise inactivate ComK (27,35).…”

DegS-DegU and ComP-ComA modulator-effector pairs control expression of the Bacillus subtilis pleiotropic regulatory gene degQ

“…Several other genes are known to be involved in the regulation of competence genes, for example, comL and csh-293 (which are thought to be part of the srfA operon), mecA, mecB, and comK (8,14,(26)(27)(28)44). Some of these regulatory genes seem to be involved as intermediates in the expression of late competence genes, since this expression could be restored by mecA or mecB mutations in strains carrying degU or comA disruptions (28).…”