Date of Award
Master of Science
Molecular Biology Microbiology and Biochemistry
Group A Streptococcus (GAS) is responsible for mild and common infections like tonsillitis and pharyngitis, and more serious invasive disorders like necrotizing fasciitis and glomerulonephritis. The ability to invade tissues is closely linked to the virulence factors expressed by the bacterium. Hyaluronic acid capsule expression is variable among all the strains in S. pyogenes and confers the capacity to evade the immune response. In a previous study, it was found that capsule production in CovR mutants was temperature-regulated, showing no capsule production at 37℃ but increased production was observed at 25℃. In this study, the objective is to ﬁnd the elements involved in the thermoregulation using a genetic approach. First, mutants were created by knocking-out CovR, the response regulator of the CovRS two-component system that controls about 15% of GAS genome. Transposon mutants were screened to ﬁnd changes in capsular phenotype. Colonies expressing capsule at 37℃ were selected for sequencing. The sequencing revealed three different events in different mutants. Two of them pointed at hypothetical proteins, one of them, SpyM3_1255, was phage associated protein with a DnaD domain and the other one, SpyM3_1377, encoded cvfA. A third over-producer mutant showed an insertion in the promoter area of the has operon, the operon that encodes for hyaluronan synthase production, upstream from other disruptions in the promoter area that generated non-producing mutants. This suggest that there is more than one factor involved in thermoregulation of capsule production.
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