Genetics of Streptococcus pneumoniae

The origins of genetics in Streptococcus pneumoniae can be traced to studies that began in the late 1800s with the isolation of nonencapsulated variants and ultimately led to the discovery of bacterial gene transfer by Griffith in 1928 and the identification of DNA as the genetic material by Avery, MacLeod, and McCarty in 1944. This chapter highlights much of the current information regarding S. pneumoniae genetics. Both transformation and conjugation have been described in S. pneumoniae. Transformation serves as the primary, and perhaps sole, means of transferring chromosomal genes. Conjugation occurs with plasmids that are capable of self-transfer or mobilization and with conjugative transposons that are integrated into the chromosome. S. pneumoniae can serve as both a donor and recipient in the conjugation of plasmid DNA and conjugative transposons. Generalized transduction has not been observed to occur, although a process termed pseudotransduction, which involves properties of both transduction and transformation, has been described for one pneumococcal bacteriophage. Some important similarities between many of the phages have been noted, and the complete nucleotide sequences have been determined for the genomes of phages Cp-1, Dp-1, EJ-1, and MM1. Replicating plasmids can be introduced into S. pneumoniae by electroporation. Unlike plasmids taken up via the natural transformation pathway, they are subject to restriction by the Dpn system, indicating that double-stranded DNA is transformed. The chapter discusses promoter activity of S. pneumoniae and the generation and analysis of mutants.