Exopolysaccharide Production and Ropy Phenotype Are Determined by Two Gene Clusters in Putative Probiotic Strain Lactobacillus paraplantarum BGCG11
ABSTRACTLactobacillus paraplantarumBGCG11, a putative probiotic strain isolated from a soft, white, artisanal cheese, produces a high-molecular-weight heteropolysaccharide, exopolysaccharide (EPS)-CG11, responsible for the ropy phenotype and immunomodulatory activity of the strain. In this study, a 26.4-kb region originating from the pCG1 plasmid, previously shown to be responsible for the production of EPS-CG11 and a ropy phenotype, was cloned, sequenced, and functionally characterized. In this region 16 putative open reading frames (ORFs), encoding enzymes for the production of EPS-CG11, were organized in specific loci involved in the biosynthesis of the repeat unit, polymerization, export, regulation, and chain length determination. Interestingly, downstream of theepsgene cluster, a putative transposase gene was identified, followed by an additionalrfbgene cluster containing therfbACBDgenes, the ones most probably responsible for dTDP-l-rhamnose biosynthesis. The functional analysis showed that the production of the high-molecular-weight fraction of EPS-CG11 was absent in two knockout mutants, one in theepsand the other in therfbgene cluster, as confirmed by size exclusion chromatography analysis. Therefore, bothepsandrfbgenes clusters are prerequisites for the production of high-molecular-weight EPS-CG11 and for the ropy phenotype of strainL. paraplantarumBGCG11.