PCR fragments can serve as donor DNA. V. cholerae wild-type strain A1552 was induced for natural competence on crab shell fragments and scored for its transformation frequency (Y-axis). Provided donor DNA was derived either from strain A1552-LacZ-Kan as a positive control (2 μg gDNA; lane 1), or from a PCR reaction according to IV in Fig. 3A. PCR-derived DNA was purified before administered to the bacteria (lane 3; 200 ng). The negative control, with no donor DNA provided, is shown in lane 2. Average of at least three independent experiments.