Genomics and Genetics of Streptococcus pneumoniae

Abstract

Ninety years after the discovery of pneumococcal Transformation, and 74 years after the work of Avery and colleagues that identified DNA as the genetic material, Streptococcus pneumoniae is still one of the most important model organism to understand Bacterial Genetics and Genomics. In this Chapter special emphasis has been given to Genomics and to Mobile Genetic Elements (the Mobilome) which greatly contribute to the dynamic variation of pneumococcal genomes by horizontal gene transfer. Other topics include molecular mechanisms of Genetic Transformation, Restriction/Modification Systems, Mismatch DNA Repair, and techniques for construction of genetically engineered pneumococcal strains.

FIGURE 1

Transformation. The model is based on information discussed in the text. In some cases, the putative regulation of gene expression may be either direct or indirect. Phosphorylation of response regulator molecules by their cognate histidine kinase sensors is indicated by P. Uptake and integration of linear DNA is shown in the lower-right portion, with monomer and dimer plasmid uptake shown in the central and lower-left portions, respectively. Plasmid uptake occurs by the same mechanism as linear DNA uptake. For monomers, complementary overlapping strands pair, and DNA synthesis completes the double-stranded circular molecule. For the dimer, a small fragment of the complementary strand can serve as a primer for DNA synthesis, and circularization can occur as described in the text. Dots on the dimer molecule indicate homologous sites.

FIGURE 2

Insertion-duplication mutagenesis and restoration. (A) The effect of using an internal gene fragment to direct insertion of a nonreplicating plasmid into the chromosome. Duplication of the target fragment occurs, and the gene is disrupted by the plasmid insertion, resulting in an insertion-duplication mutation. (B) The target fragment overlaps the ends of two genes. Insertion results in duplication of the target fragment, but both genes are completely reconstructed, and the result is an insertion-duplication restoration. Both genes should be functional, unless they form part of an operon, in which case the plasmid insertion would be polar on the downstream gene. The figure shows a selectable erythromycin-resistance gene (erm) and a promoterless chloramphenicol-resistance reporter gene (cat).