Regulation of virulence factors

• there is a very important contribution of the growth phase

• during exponential growth, lots of surface proteins are expressed

• during stationary growth, lots of exotoxins are expressed

Density-dependent gene regulation

• this is also called quorum sensing

• bacteria can “sense” population size

• a high cell density means released molecules are sensed and alter gene expression

The agr locus mediates this

• peptide accumulates in media

• when it reaches a certain level, AgrC senses it

• this activates AgrA

• AgrA directly affects gene transcription via RNAIII (cf. http://en.wikipedia.org/wiki/RNAIII)

• this alters expression, decreasing coagulase and fibrinogen-binding protein and increasing levels of some exoproteins

RNAIII inhibitor in agr system

• RNAIII has a bagpipe structure

• it can upregulate or downregulate various factors

• overall, agr mutants seem to have decreased virulence compared to wild-type although these organisms have increased expression of a variety of genes

Synchronous expression of agr

• the bacteria are working as a population

Category: Microbiology Notes