FIG. 4.

Influence of LytA on efficiency of gene exchange in vitro. Two LytA-deficient S. pneumoniae strains, H3 (Nov^r) and H6 (Rif^r), were mixed at three different densities (OD₅₅₀s of 0.1, 0.2, and 0.4) and induced to competence by adding 250 ng of CSP-1/ml. After cocultivation for 1.5 h, cells were plated onto agar plates containing rifampin and novobiocin and incubated at 37°C. Transformants were scored the next day. The two strains H1 (Nov^r) and A1 (Rif^r), both containing intact lytA genes, were treated in the same way. Black columns represent numbers of transformants obtained by cocultivation of H1 and A1, while white columns represent numbers of transformants obtained by cocultivation of the LytA-deficient strains H3 and H6. Values shown are numbers of CFU of transformants per milliliter and are the means ± standard errors of results for triplicate samples. Uninduced samples, receiving no peptide pheromone, were run in parallel as negative controls. The numbers of transformants observed in uninduced samples ranged from 0 to 200 CFU/ml.