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J. Bacteriol., Jan 1998, 338-349, Vol 180, No. 2
TA Russo, S Wenderoth, UB Carlino, JM Merrick and AJ Lesse
Group III capsular polysaccharides (e.g., K54) of extraintestinal isolates
of Escherichia coli, similar to group II capsules (e.g., K1), are important
virulence traits that confer resistance to selected host defense components
in vitro and potentiate systemic infection in vivo. The genomic
organization of group II capsule gene clusters has been established as a
serotype-specific region 2 flanked by regions 1 and 3, which contain
transport genes that are highly homologous between serotypes. In contrast,
the organization of group III capsule gene clusters is not well understood.
However, they are defined in part by an absence of genes with significant
nucleotide homology to group II capsule transport genes in regions 1 and 3.
Evaluation of isogenic, TnphoA-generated, group III capsule-minus
derivatives of a clinical blood isolate (CP9, O4/K54/H5) has led to the
identification of homologs of the group II capsule transport genes kpsDMTE.
These genes and their surrounding regions were sequenced and analyzed. The
genomic organization of these genes is distinctly different from that of
their group II counterparts. Although kps(K54)DMTE are significantly
divergent from their group II homologs at both the DNA and protein levels
phoA fusions and computer-assisted analyses suggest that their structures
and functions are similar. The putative proteins Kps(K54)M and Kps(K54)T
appear to be the integral membrane component and the peripheral ATP-binding
component of the ABC-2 transporter family, respectively. The putative
Kps(K54)E possesses features similar to those of the membrane fusion
protein family that facilitates the passage of large molecules across the
periplasm. At one boundary of the capsule gene cluster, a truncated kpsM
(kpsM(truncated) and its 5' noncoding regulatory sequence were identified.
In contrast to the complete kps(K54)M, this region was highly homologous to
the group II kpsM. Fifty-three base pairs 3' from the end of
kpsM(truncated) was a sequence 75% homologous to the 39-bp inverted repeat
in the IS110 insertion element from Streptomyces coelicolor. Southern
analysis established that two copies of this element are present in CP9.
These findings are consistent with the hypothesis that CP9 previously
possessed group II capsule genes and acquired group III capsule genes via
IS110-mediated horizontal transfer.
Copyright © 1998, American Society for Microbiology
Identification, genomic organization, and analysis of the group III capsular polysaccharide genes kpsD, kpsM, kpsT, and kpsE from an extraintestinal isolate of Escherichia coli (CP9, O4/K54/H5) [In Process Citation]
Department of Medicine, and The Center for Microbial Pathogenesis, SUNY at Buffalo, New York 14215, USA. trusso@acsu.buffalo.edu
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