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

elated genomic islands and this restriction fragment was not presence in the E106-
serW EcoRV RFLP.
3.3.2 Analysis of E106-serW CRISPR system
This subsection aims to provide a brief overview of CRISPR systems. This is
followed by discussion and comparison of the E106-serW CRISPR system to other
CRISPR systems identified in the literature and databases.
The CRISPR system is found in a wide range of bacterial species, it is currently
found among 24 individual sequenced species ranging from P. aeruginosa PA14,
Enterobacter spp 638 to Yersinia pestis. A CRISPR system consists of two
components; the CRISPR array and the CRISPR-associated proteins. The CRISPR
array consists of a number of palindromic repeat DNA sequences separated by DNA
spacers of species-defined length. These CRISPR array are found in close proximity
to a set of proteins known as CRISPR-associated proteins (Cas proteins). The
CRISPR-associated proteins are divided into two categories. The first category is
the core set of cas genes of which there are 6 (Peterson et al. 2001) named cas1 to
cas6. All genomes containing a CRISPR system contain cas1 and one or more of
the additional core cas genes (Jansen et al. 2002). The second category of genes
associated with CRISPR systems define the subtype which are usually species
related, there are 7 to 8 subtypes (Sorek, Kunin & Hugenholtz 2008).
The role of CRISPR systems has only recently been elucidated and is shown in
Figure 3-11. The CRISPR system is suggested to work in a RNA interference
dependent manner (Sorek, Kunin & Hugenholtz 2008). The DNA spacers between
the CRISPR repeats have identified as bacteriophage DNA. The CRISPR system
acts to generate small RNAs that bind to complementary bacteriophage DNA which
triggers degradation of the bacteriophage DNA. This acts to protect the bacterium
from infection.
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