Transcriptional analysis of beta-lactamase regulation in Bacillus licheniformis

Abstract

The expression of the blaP gene for the beta-lactamase of Bacillus licheniformis was examined by transcriptional analyses. Radiolabeled probes containing the blaP gene or various regions 3' or 5' to it were used to analyze RNA samples prepared from induced and uninduced cultures of wild-type and mutant B. licheniformis strains. The level of blaP mRNA was low in uninduced wild-type cells. At 37 degrees C, blaP mRNA levels reached a maximum 1 h after induction while rising up to 180-fold and then declined, but remained severalfold above the uninduced level for several hours. The rate of beta-lactamase synthesis was roughly proportional to the levels of blaP mRNA in both wild-type and mutant strains, indicating that regulation of beta-lactamase formation occurs primarily at the level of transcription. Turnover of blaP mRNA in the presence of rifampin was rapid, giving a blaP mRNA half-life of about 2 min. Yet, high levels of blaP mRNA were maintained for at least 1 h after removal of free inducer. Three blaP mRNAs of 1.2, 2.9, and 3.4 kilobases were produced from the blaP promoter. The most abundant made up about 97% of all blaP transcripts and was also the smallest, ending at a transcriptional terminator located about 60 bases 3' to the blaP structural gene. Variables such as incubation temperature, cytotoxicity of inducer, and type of strain had essentially no effect on the ratio of large blaP mRNA to total blaP mRNA. The 2.9- and 3.4-kilobase blaP mRNAs identify potential locations of genetically linked regulators of beta-lactamase synthesis.