Comparative genome analysis reveals strains specific gene clusters involved in exopolysaccharides biosynthesis in Lactobacillus plantarum

Several lactic acid bacteria (LAB) produce capsular and secreted forms of exopolysaccharides (EPS) (Remus et al., 2012). The EPS production is correlated to the presence of specific gene clusters (eps/cps) which exhibit a conserved modular organization and include genes encoding both regulatory factors and enzymes involved in EPS biosynthesis, polymerization and secretion, including glycosyl-transferases, which are responsible for the assembly of the characteristic EPS-repeating unit. The Lactobacillus plantarum WCFS1 genome encodes 4 cps clusters of genes that are associated with surface polysaccharide production. The cps2A-J and cps4A-J clusters encode all functions required for capsular polysaccharide formation, while the cps1A-I and cps3A-J clusters lack genes encoding chain-length control functions and a priming glycosyl-transferase (Remus et al., 2012). L. plantarum Lp90 exhibited a ropy phenotype which was associated to its capacity to produce EPS. The genetic basis of EPS production was investigated by identification, sequencing and comparative analysis of genes clusters involved in EPS biosynthesis with other L. plantarum genomes. It was found that the cluster 4 (cps4) is the most conserved, while the cluster 3 presents high homology with cps3 of WCFS1, ST-III and ATCC 14917 L. plantarum strains. Conversely, cluster 1 (cps1) is fully present only in L. plantarum JDM1, while the first genes of cluster 2 are homologous to the cps2A-E genes of other L. plantarum. The remaining genes of cluster 2 are homologous to proteins of Lactobacillus fabifermentans T30PCM01, probably involved in the exopolysaccharides biosynthesis. This feature makes unique the organization of cps clusters L. plantarum Lp90 and may explain the ropy phenotype of this strain.