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independently of its polysaccharidic structure. Likewise, the ABC-depen-
dent assembly and export pathway requires the participation of the KpsD.
Although this protein possesses the PES domain characteristic of the OPX
proteins, it is not a lipoprotein and shares low sequence similarity with
Wza (
Cuthbertson et al., 2009
). Considerably, less is known about a pos-
sible interaction between the OPX and PCP-3 components involved in
the ABC-dependent pathway. However, existing data suggest that KpsD
and KpsE may form a complex similar to that of Wza and Wzc (
Cuthb-
ertson et al., 2009
).
2.4. Organization and Phylogeny of Gene Clusters Involved
in EPS Biosynthesis
In most EPS-producing bacteria, the genes encoding the proteins
involved in the synthesis, assembly and export of the EPS are located in
the same genetic loci, exhibiting conserved features (
Yother, 2011
). In
E. coli
, the genetic loci encoding the proteins involved in the production
of group 1 capsules, following the Wzy-dependent pathway, comprise
two distinct regions. The 5′ region contains conserved genes, including
wza
,
wzb
, and
wzc
. The 3′ region is serotype specific and encodes the
enzymes involved in the biosynthesis of the nucleotide sugars, glyco-
syltransferases and Wzx and Wzy proteins. While the genes related to
nucleotide sugar metabolism and those encoding the glycosyltransferases
are serotype specific, determining the monosaccharidic composition of
the capsules produced, the
wzy
and
wzx
are always present, defining the
pathway (
Whitfield, 2006
). This 3′ region is identical in loci involved in
the production of other polysaccharides by the Wzy-dependent pathway,
such as the
E. coli
group 4 capsules and the O-antigen of LPS in different
bacteria (
Whitfield, 2006
).
The organization of the genetic loci involved in the production of group
1 capsules can be found in other organisms, including several strains of the
Burkholderia
genus (
Ferreira et al., 2010
;
Moreira et al., 2003
) and
Klebsiella
pneumoniae
(
Rahn, Drummelsmith, & Whitfield, 1999
). The gene clusters
of
E. coli
and
Klebsiella
are highly conserved in organization and nucleo-
tide sequence, raising the hypothesis of horizontal gene transfer (HGT)
events between these organisms. The same organization can also be found
in Gram-positive bacteria, such as
Streptococcus pneumoniae
(
Yother, 2011
)
and several lactic acid bacteria (
De Vuyst, De Vin, Vaningelgem, & Degeest,
2001
;
Jolly & Stingele, 2001
), despite the inherent differences related to the
cell wall structure.
