The Bacillus subtilis menCD promoter is responsive to extracellular pH

Activation kinetics of a Bacillus subtilis menaquinone biosynthetic gene promoter (the menCD promoter) were measured during growth and sporulation, with the aid of a menCD-lacZ translational gene fusion. Transient maximal activation was seen shortly after the end of exponential growth in unbuffered complex medium containing a low glucose concentration. These activation kinetics were correlated with transient acidification of the medium under conditions permitting TCA cycle function during the post-exponential period, while mutations that blocked TCA cycle function (cit mutants) were associated with sustained acidification and promoter activation during this period. In cit⁺ strains, buffering of the medium to pH 5.7 caused sustained maximal activation, while buffering to pH 7.2 prevented enhancement of activation. The menCD promoter appears to be responsive to extracellular acidic pH.