Bacillus subtilis citB gene is regulated synergistically by glucose and glutamine

The activity of aconitase in Bacillus subtilis is greatly reduced in cells cultured in media containing rapidly metabolized carbon sources (e.g., glucose). Thus, expression of this enzyme appears to be subject to a form of catabolite repression. Since the product of the citB gene of B. subtilis is required for aconitase activity, we cloned the wild-type allele of this gene and used this DNA as a probe for transcription of citB in cells grown in various media. The steady-state level of RNA that hybridized to this probe was about 10-fold higher in B. subtilis cells grown in citrate-glutamine medium than in cells grown in glucose-glutamine medium. This result correlates well with the steady-state levels of aconitase activity. Two transcripts were shown to initiate within the cloned DNA; the steady-state level of one of these transcripts varied in the same way as did aconitase activity when cells were grown in media containing different carbon sources. This is the first demonstration of regulation by the carbon source of the level of a vegatative-cell transcript in B. subtilis.