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capsule export via the ABC-dependent pathway, with defects on these pro-
teins leading to the accumulation of the polymer inside the cell (
Cieslewicz
& Vimr, 1996
;
Whitfield, 2006
).
The pattern of the genes encoding the Wz_ and Kps_ homologues was
consistent with that observed previous for cyanobacteria, with the gene
copies scattered throughout the genomes, either isolated or in small clusters
(
Pereira et al., 2009
). It is possible that this pattern results from intragenomic
duplication events and/or HGT. Given that gene duplication generates a
broad adaptive potential, some of the copies may be related to specific phe-
notypes such as strains' morphology and ecological niches. Thus, it is impor-
tant to unveil the evolutionary events that led to the pattern observed for
these genes in cyanobacteria.
Due to the pivotal roles of PCP and OPX proteins in EPS assembly and
export pathways, special attention was given to these proteins. The diversity
and phylogenetic relationship of several Gram-negative PCP and OPX rep-
resentatives were recently reviewed (
Cuthbertson et al., 2009
). In general,
the major phylogenetic groups defined for the PCP proteins matched those
established for the correspondent OPX protein (present in the same gene
cluster), likely reflecting their co-evolution. As a result, six groups of EPS
assembly and export components were identified, where groups A, C, D,
and E follow the Wz-dependent pathway and groups B and F participate in
the ABC-dependent pathway. Within each group, the proteins from differ-
ent bacteria display similar characteristics (high sequence similarity, domain
organization, etc.). Although this study provided an important update in the
knowledge of bacterial EPS assembly and export, cyanobacteria have not
been contemplated (
Cuthbertson et al., 2009
). To increase our understand-
ing on cyanobacterial EPS assembly and export, the putative PCP and OPX
identified were analysed from an evolutionary perspective. To achieve that,
phylogenetic trees were computed using the Maximum Likelihood (ML)
(
Felsenstein, 1981
) and the Neighbour-Joining (
Saitou & Nei, 1987
) algo-
rithms, and compared to that obtained from the 16S rRNA. Regarding this
last tree, the major clusters obtained are in agreement with the phylogenetic
relationships described for cyanobacteria, determined using a single gene/
protein or sequence concatenation methods (
Larsson et al., 2011
;
Swingley
& Blankenship, 2008
). In general, the clusters identified in the ML and NJ
computed trees were consistent, strengthen the proposed model. The data
gathered in this work provide the first insight in the evolutionary history
of EPS-related genes in cyanobacteria. Most importantly, it defined new
relevant questions and created the conditions for the design of new
in silico
,
