Natural Genetic Transformation: A Direct Route to Easy Insertion of Chimeric Genes into the Pneumococcal Chromosome

The ability of Streptococcus pneumoniae (the pneumococcus) to transform is particularly convenient for genome engineering. Several protocols relying on sequential positive and negative selection strategies have been described to create directed markerless modifications, including deletions, insertions, or point mutations. Transformation with DNA fragments carrying long flanking homology sequences is also used to generate mutations without selection but it requires high transformability. Here, we present an optimized version of this method. As an example, we construct a strain harboring a translational fusion ftsZ-mTurquoise at the ftsZ locus. We provide instructions to produce a linear DNA fragment containing the chimeric construction and give details of the conditions to obtain optimal pneumococcal transformation efficiencies.