Streptococcus mitis: successful adaptation of the pneumococcus to mutualistic lifestyle

Series Name Leicester Microbial Sciences and Infectious Disease Network (LeMID)
Speaker Professor Mogens Kilian, Department of Bioscience, Aarhus University, Denmark
Type Lectures & Talks
When 14 Nov 2017, 12:00PM - 01:00PM
Venue Bennett LT2
Open To University staff and students
For Bookings Contact no need to book
The bacterium Streptococcus pneumoniae is one of the leading causes of fatal infections affecting humans. Intriguingly, phylogenetic analysis shows that the species constitutes one evolutionary lineage in a cluster of the otherwise commensal Streptococcus mitis population, with which humans live in harmony. In a comparative analysis of 60 genomes, including phylogenetic analyses of all predicted genes, we have shown that the pathogenic pneumococcus evolved into a master of genomic flexibility while lineages that became the nonpathogenic S. mitis secured harmonious coexistence with their host by stabilizing an approximately 15%-reduced genome devoid of many virulence-associated genes. Detailed examination shows that interspecies gene transfer between S. pneumoniae and S. mitis occurs in a unidirectional manner, i.e., from S. mitis to S. pneumoniae. Import of genes from S. mitis and other Mitis, Anginosus, and Salivarius group streptococci ensured allelic replacements and antigenic diversification of S. pneumoniae, and has been driving the evolution of the remarkable structural diversity of capsular polysaccharides. This explains how the unique structural diversity of the pneumococcal capsule evolved and conceivably will continue to evolve and reveals a striking example of the fragile border between the commensal and pathogenic lifestyles. While genomic plasticity enabling quick adaptation to environmental stress is a necessity for the pathogenic streptococci, the commensal lifestyle benefits from stability. This evolutionary scenario provides a unique opportunity for identification of virulence-associated properties.

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