Biology Reference
In-Depth Information
self-transmissible plasmid due to the presence of the highly conserved
tra
locus
(
Brinkley et al., 2006
). The complete
tra
region is only found in representatives
of the EPEC1 clonal group (
Tobe et al., 1999
;
Brinkley et al., 2006
), confirm-
ing previous findings that some EAF plasmids can be mobilized to other
E. coli
strains by conjugation (
Baldini et al., 1983
;
Laporta et al., 1986
;
McConnell
et al., 1989
) while others cannot be transmitted as they lack the required transfer
genes (
Hales et al., 1992
;
Tobe et al., 1999
).
Two loci important for pathogenicity on the EAF plasmid are the type IV
BFP gene cluster (
bfpT,
) and the
per
locus encoding for transcriptional activators.
The EAF plasmid also regulates the expression of the
eae
gene, located in the
chromosomal pathogenicity island LEE (
Jerse and Kaper, 1991
) (see below).
Bundle-forming pili
BFP is a member of the type IV-B class of fimbriae that are produced by a
number of Gram-negative pathogenic bacteria (e.g. ETEC,
Salmonella ener-
ica
serovar Typhi and
Vibrio cholerae
). BFPs form ropelike bundles extending
from the cell surface of typical EPEC strains (
Girón et al., 1991
). These pili are
important virulence factors and are required for LA to epithelial cells (
Donnenberg
et al., 1992a
), autoaggregation and virulence in volunteers (
Bieber et al., 1998
;
Knutton et al., 1999
).
The
bfpT,
operon consists of 14 genes, all of which are required for BFP bio-
genesis (
Ramer et al., 1996
;
Sohel et al., 1996
;
Stone et al., 1996
;
Anantha et al.,
2000
;
Blank and Donnenberg, 2001
;
Schreiber et al., 2002
;
Hwang et al., 2003
).
Expression of this gene cluster in a laboratory strain of
E. coli
via a plasmid
confers both LA and BFP biogenesis (
Stone et al., 1996
). BFP is composed of
repeating subunits of bundlin, pilin monomers encoded by
bfpA,
the first gene
in the
bfpT,
operon.
bfpA
encodes pre-bundlin, which is processed by the pre-
pilin peptidase, encoded by
bfpP
, producing mature bundlin (
Donnenberg et al.,
1992a,b
;
Zhang et al., 1994
). Mutation of the
bfpA
gene leads to loss of LA and
autoaggregation (
Donnenberg et al., 1992a
;
Bieber et al., 1998
;
Anantha et al.,
2000
).
Structural analysis of bundlin revealed that while EPEC and
Vibrio
cholerae
show distinct differences in their monomer subunits and are unable
to complement one another, they assemble into filaments with similar helical
organization (
Ramboarina et al., 2005
). The genes in the
bfpT,
operon are reg-
ulated by environmental and host factors together with a
p
lasmid
e
ncoded
r
egulator, Per (
Puente et al., 1996
;
Rosenshine et al., 1996a
;
Martínez-Laguna
et al., 1999
). For more detailed information on BFP and other type IV pili, see
Chapter 13.
per
(plasmid-encoded regulator)
The
per
operon consists of three ORFs, designated
perA, perB
, and
perC
,
which are also known as
bfpT
,
bfpV
, and
bfpW
, respectively.
perA
, the first
Search WWH ::
Custom Search