5 The role of quorum-sensing in the virulence of Pseudomonas ...

Unfortunately, 65% of the ORFs within PAPI-1 have no known function and are
labelled as hypothetical genes (He et al. 2004). These that have been assigned
function and have sufficient literature are evaluated in the subsection.
There are two, two component regulatory systems (TCS) within PAPI-1 that have
been highlighted through previous infection studies as important for general
virulence of the strain. Two component regulatory systems act to change the gene
expression within a cell to favour changes in the external environment. They
consists of two parts, one the sensor kinase, which senses the changes in the
environment by being bound to the cellular membrane and two, the response
regulator, which mediates the intracellular response to the changes in environment.
The published data in conjugation with the data generated during this project,
suggests that the two TCS are important for mammalian infection, as the differences
in virulence are currently only noted in mice models of infection.
The TCS involving RcsC and RcsB described in the literature is involved in the
adaptation of the cell surface by changing its structure and integrity (Huang,
Ferrieres & Clarke 2006). In E. coli there are three components involved in this
system, RcsC, the sensor kinase, which activates RcsD, an intermediate, which in
turn activates RcsB, the response regulator. A RcsD homologue has not been
discovered in P. aeruginosa PA14, but the literature suggest that the Yersinia spp.
genome does not encode a functional RcsD and the TCS has taken on a different
role (Huang, Ferrieres & Clarke 2006). As this TCS, is now found on a
pathogenicity island rather than the core genome and does not encode the
intermediate protein RcsD, suggests the TCS is now performing some auxiliary role
crucial to PAPI-1. This is supported by the fact that mutagenesis of either RcsB or
RcsC results in attenuation in other models of infection (He et al. 2004),
demonstrating that they are functional.
In the circumstances that the rcs TCS system maintained its usual functional
activities the loss of RcsB or RcsC would result in cells that have a reduced ability
to create a capsule and to form biofilms. A capsule is a highly noted protection of
bacteria from the host innate immunity. This phenomenon could contribute to the
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