Saville, Alison Maren
Investigation of the role of a large serine rich
repeat protein in Streptococcus pneumoniae.
PhD thesis, University of Glasgow.
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Streptococcus pneumoniae is a genetically diverse organism that varies substantially in its genomic content from one strain to another. Current therapeutic strategies in the management of pneumococcal disease include treatment with antibiotics and prevention by vaccination. However, due to the highly competent nature of the bacterium the prevalence of antibiotic resistance and vaccine escape is increasing. The pneumococcus causes a wide range of diseases, and this can be attributed to both the succeptibility of the human host and the genetic background of the infecting strain. The study of the contribution of variations in the genome of S.pneumoniae is clearly important in understanding the behaviour of this organism, and managing the burden of disease relating to this organism.
S.pneumoniae strains are able to acquire DNA from other strains, and also from other closely related species, who occupy the same niche in the human host. One region of genomic diversity in the pneumococcus encodes a large serine rich repeat protein, glycoysltransferases and secretion proteins, some of which are homologous to the Sec secretion pathway. Similar loci have been characterised and found to be important in the virulence of other gram positive bacteria, including S.gordonii and S.parasanguinis.
The presence of this locus was investigated in a diverse population of pneumococcal isolates, and shown to be present in a wide variety of isolates. The RNA of genes in the locus was found to be expressed. Expression of the SRR protein, encoded by SP1772, was investigated; a role in biofilm formation was identified utilising an isogenic mutant in SP1772 of TIGR4. In addition, the gene encoding the SRR was found to be able to recombine within a single strain of S.pneumoniae, suggesting this region of the genome is not only variable in its presence in the pneumococcal population but also able to adapt to the environment it is in.
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