A new integrative reporter plasmid for Streptococcus pneumoniae

A new promoter probe system for Streptococcus pneumoniae has been developed that allows stable genomic integration of promoters cloned in front of a promoterless hybrid beta-galactosidase gene consisting of translation initiation signals of the protease gene htrA of S. pneumoniae fused to a truncated Escherichia colibeta-galactosidase gene lacZ. Chromosomal insertions of promoter-lacZ fusions are directed to the endogenous beta-galactosidase gene bgaA, thereby abolishing background beta-galactosidase activity. The new system was tested by measuring beta-galactosidase activity directed by the two promoters of the early competence genes comA and comC. The new integrative plasmid offers several advantages compared with existing systems and is especially suited for stable integration of small promoter fragments to conduct mutagenesis or deletion studies.