PCR ligation mutagenesis in transformable streptococci: application and efficiency

PCR ligation mutagenesis is a novel technique that can easily be adapted for many gene modification purposes. Successful application of this versatile technique involves sequence identification of the target gene region, creation of a mutagenic construct consisting of two gene-flanking proximal sequences specifically ligated to a selectable marker, and incorporation of this construct into the genome via genetic transformation and homologous recombination. In this study, we demonstrate the use of PCR, followed by restriction digestion and re-ligation to generate transforming constructs for the rapid deletion of open reading frames in transformable streptococci. Moreover, we characterized the dependence of transformation efficiency for mutant generation on the length of the homologous regions harbored by the mutagenic construct. Our results indicated that PCR ligation mutagenesis could be reliably employed for the systematic generation of gene deletion mutants in both highly transformable Streptococcus mutans and S. pneumoniae. Evaluation of the method showed a strong influence of the length of homologous flanking region on integration efficiency.