FIGURE 14.

Production of the K. lactis killer toxin is enhanced in LSM1 and PAB1 deletion strains. Growth curves and production of the pGKL1 killer toxin from the K. lactis IFO1267 (blue), IFO1267 pbp1Δ (red), IFO1267 lsm1Δ (gray), and IFO1267 pbp1Δ pab1Δ (green) strains. All strains were grown in YPD medium at 28°C for approximately 80 h, and their OD_{600 nm} and toxin production were monitored. Production of the pGKL1 killer toxin in culture medium was assayed by a well diffusion test on YPD agar plates with a lawn of the S. cerevisiae S6/1 sensitive strain (for details of the method, refer to section Materials and Methods and Supplementary Figure S4). The toxin levels in culture media in the early stationary phase (∼35 h), when all the cultures reached a comparable OD₆₀₀, are depicted. The amount of active toxin produced by each strain is presented as the calculated normalized inhibition zone at killer toxin saturation (I_s). Growth curves and I_s determination correspond to at least three independent replicates. The results were statistically evaluated using one-way ANOVA followed by post hoc Tukey’s HSD test and further confirmed with Scheffé multiple comparison (^∗∗p < 0.01). Normal distribution of the data was confirmed by the Shapiro–Wilk test. Error bars at each point on the growth curves and in the bar graph represent standard deviation.