| Summary: | The members of microbial community communicate with each other by using quorum sensing (QS) systems, and modulate their collective ‘behavior‘ for in host colonization and virulence, biofilm formation, interspecies competition, and environmental adaptation. Recent influx in genome data availability reveals the presence of several putative QS sensing circuits in microbial pathogens, but many of these have not been functionally characterized despite their utility as drug targets. To increase the repertoire of functionally characterized QS systems in bacteria, we studied Rgg144/Shp144 and Rgg939/Shp939, two putative QS systems in the important human pathogen Streptococcus pneumoniae. I find that both of these QS circuits are induced by short hydrophobic peptides (Shp) upon sensing sugars found in the respiratory tract, such as galactose and mannose. Microarray analysis using cultures grown on mannose and galactose revealed that the expression of large number of genes is controlled by these QS systems, especially those encoding for essential physiological functions and virulence related genes such as the capsular locus. Moreover, the array data revealed evidence for cross talk between these systems. Finally, these Rgg systems play a key role in colonisation and virulence, as deletion mutants of these QS systems are attenuated in the mouse models of colonisation and pneumonia.
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