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involved in synthesis and assembly of group 3 capsules, also by the ABC-
dependent pathway, although fewer characteristic conserved genes are
present and their positions and relative order differ from that observed for
group 2 capsules-related loci (
Whitfield, 2006
).
3. GENETICS OF CYANOBACTERIAL EPS
PRODUCTION: CURRENT KNOWLEDGE
The first insight into the genes encoding proteins involved in EPS
assembly and export (hereafter referred to as EPS-related genes) in cya-
nobacteria was obtained recently (
Pereira et al., 2009
). In that study, the
authors performed an
in silico
analysis of available cyanobacterial genome
sequences, revealing the existence of genes coding for proteins that possess
the conserved domains involved in bacterial EPS assembly and export. The
results obtained also showed that in cyanobacteria, the EPS-related genes
often occur in multiple copies scattered throughout the genomes, either
isolated or in small clusters (
Fig. 7.4
) (
Pereira et al., 2009
).
Although gene redundancy is not unusual in cyanobacteria (
Larsson,
Nylander, & Bergman, 2011
), the pattern observed for EPS-related genes is
different from that of other bacteria, where the EPS-related genes are usually
clustered (
De Vuyst & Degeest, 1999
;
Ferreira et al., 2010
;
Jolly & Stingele,
2001
;
Rahn et al., 1999
;
Roberts, 1996
;
Whitfield, 2006
). In general, as the
complexity of the cyanobacterial strain/size of genome increases, more copies
of the EPS-related genes are found (
Pereira et al., 2009
). It is possible that some
of these genes encode proteins that play similar functions in closely related
pathways, such as the production of O-antigen of the LPS, thus possessing
the same functional domains and/or annotation. However, this hypothesis
does not account for the multiple genes encoding putative OPX proteins
since, up to this moment, there is no evidence of an interaction between the
PCP-1 proteins involved in the assembly and export of the O-antigen with
a Wza/KpsD homologue. Nevertheless, the presence of multiple genes cod-
ing for OPX proteins has also been reported for other bacteria, including
Burkholderia
and
Bacteroides
species (
Cuthbertson et al., 2009
). In the case of
heterocystous strains, it is also necessary to take into consideration the biosyn-
thesis of the polysaccharidic layer surrounding the heterocysts (
Cardemil &
Wolk, 1976
,
1979
,
1981a
,
1981b
;
Dunn & Wolk, 1970
). The identification of
genes encoding proteins possessing the domains typically found in Wzx and
Wzy, both characteristic of theWzy-dependent pathway, strongly suggests that
cyanobacterial EPS production follows this mechanism (
Pereira et al., 2009
;
