FIG 4.

Deletion of pcfFEG or pcfRK increases susceptibility of A12 to the lantibiotic nisin. (A) Tolerance of A12 strains to different concentrations of nisin measured by monitoring growth OD₆₀₀ over a 24-h period. Overnight cultures were subcultured into fresh BHI medium. Once the OD₆₀₀ reached 0.5, cultures were diluted 1:100 into fresh BHI medium containing various concentrations of nisin and growth was monitored in a Bioscreen C. (B) Expression of pcfFEG mRNA was measured using qRT-PCR in the wild-type and pcfRK strain. Overnight cultures were inoculated into fresh BHI medium and once cultures reached OD₆₀₀ 0.5, cells were collected for RNA extraction and subsequent qRT-PCR. (C) Expression of pcfFEG and pcfRK in A12 in response to treatment with 2 μg/ml of nisin. RNA was extracted from mid-exponential-phase cells of A12 left untreated or treated with nisin for subsequent qRT-PCR. All experiments were done in biological triplicates with technical triplicates. Error bars represent SDs, and statistical analysis was performed using an unpaired Student t test. *, P < 0.05; **, P < 0.01; ***, P < 0.001.