Lactobacillus delbrueckii subsp. bulgaricus OLL1073R-1 eps gene knockout mutants reduced exopolysaccharide synthesis and immunomodulatory activities

In this study, eps genes in Cluster I of Lactobacillus delbrueckii subsp. bulgaricus OLL1073R-1 were deleted via conjugal transformation to understand the role of key eps genes in exopolysaccharide (EPS) synthesis and their immunomodulatory effects. Eps gene knockout mutants of OLL1073R-1, ΔepsIB, ΔepsIC, ΔepsID, ΔepsIE, and ΔepsIF were isolated by homologous recombination with the conjugative plasmid pGMβ1. Significant reductions in high molecular weight EPS (H-EPS) production were observed in ΔepsIB, ΔepsIC, and ΔepsIE and partly in ΔepsIF but not in ΔepsID fermented milk. H-EPS purified from OLL1073R-1 fermented milk showed significant induction of IL-6, IL-10 and IL-12, whereas low molecular weight EPS (L-EPS) showed significant induction of IL-10 and IL-12 in THP-1 dendritic cells. ΔepsIE with less production of H-EPS exhibited significant reductions in IL-6, IL-10 and IL-12 productions. The present study firstly reported that H-EPS in OLL1073R-1 contributes to IL-6, IL-10 and IL-12 productions in THP-1 dendritic cells.