Method for introducing specific and unmarked mutations into the chromosome of Streptococcus pneumoni

This work describes a procedure for the generation of site-specific mutations into the chromosome of Streptococcus pneumoniae that does not involve the use of an antibiotic resistance marker. A linear fragment of transforming deoxyribonucleic acid (DNA) is constructed by polymerase chain reaction (PCR) (gene splicing by overlap extension) and used to transform competent cells of S. pneumoniae . Selection of transformants is performed by PCR, and typically, 1% of the transformed cells show the expected mutation. By this protocol it is possible to change a single base pair into the pneumococcal genome, as well as obtaining in-frame deletions and insertions.