The surface macromolecules of probiotic bacteria play crucial roles in modulating immune responses in the host. Exopolysaccharide (EPS) from lactic acid bacteria (LAB) have been widely reported to exhibit immunomodulatory activity. In this study, the EPS biosynthesis gene cluster of Lacticaseibacillus paracasei S-NB was analyzed and a deletion mutant S-NBΔ7576 (two genes S-NB_2175/wze and S-NB_2176/wzd were responsible for the chain length determination and export of EPS) was successfully constructed, resulting a 40.02% decrease in the production of EPS. The deletion of wze and wzd had little effect on the monosaccharide composition and major groups of the two EPS fractions (BEPS1 and BEPS2). Both BEPS1 and BEPS2 could inhibit the transcriptional level of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) mRNA in RAW 264.7 cells induced by lipopolysaccharide (LPS), and enhance host immune tolerance via suppressing NF-κB and MAPK signaling. Notably, the S-NBΔ7576 mutant supplied with the BEPS1/BEPS2 exhibited more significant inhibition of cytokines production and the phosphorylation of p65 and c-Jun N-terminal kinase (JNK) in LPS-stimulated cells compared with the S-NBΔ7576 mutant alone. Our study provided the immunomodulatory effect of BEPS1 and BEPS2 from L. paracasei S-NB, in which the wze and wzd genes associated with EPS biosynthesis may play an important role.

In this study, the in vitro digestion and fermentation of two intra-polysaccharide fractions (IPS1 and IPS2) from Paecilomyces cicadae TJJ1213 were investigated. The constituent monosaccharides of IPS1 and IPS2 were not changed after simulated saliva, gastric and small intestinal digestion. However, they can be hydrolyzed and utilized by gut microbiota, and short-chain fatty acids (SCFAs) level were increased after IPS1and IPS2 treatments. Furthermore, 16S rRNA sequencing analysis of fermentation samples were performed. Alpha-diversity, beta-diversity and taxonomic composition differences analysis revealed that IPS1 and IPS2 promoted the proliferation of beneficial bacteria and modulated the overall structure of gut microbiota. Taxonomic comparison analysis found that IPS1 increased the relative abundances of beneficial bacteria including Megamonas, Bifidobacterium and Lactobacillus, while IPS2 could increase the abundance of Bacteroides, Parabacteroides and Phascolarctobacterium. In addition, they can also decrease the levels of pathogenic bacteria containing Escherichia-Shigella, Klebsiella and Fusobacterium. These results indicated that IPS from Paecilomyces cicadae TJJ1213 could be used as potential candidates for new functional foods.