The microbiota is directly involved in the development and modulation of the intestinal immune system. In particular, members of the genus Bifidobacterium play a primary role in immune regulation. In the present study, Bifidobacterium bifidum H3-R2 was screened from 15 bifidobacterium strains by in vitro experiment, showing a positive tolerance to digestive tract conditions, adhesion ability to intestinal epithelial cells and a regulatory effect on immune cell activity. Immunostimulatory activity of B. bifidum H3-R2 was also elucidated in vivo in cytoxan (CTX)-treated mice. The results showed that the administration of B. bifidum H3-R2 ameliorated the CTX-induced bodyweight loss and imbalanced expression of inflammatory cytokines, enhanced the production of secretory immunoglobulin A (SIgA), and promoted splenic lymphocyte proliferation, natural killer (NK) cell activity and phagocytosis of macrophages in immunosuppressed mice. In addition, B. bifidum H3-R2 restored injured intestinal mucosal, and increased the villus length and crypt depth in CTX-treated mice. The results could be helpful for understanding the functions of B. bifidum H3-R2, supporting its potential as a novel probiotic for immunoregulation.

Lactobacillus plantarum, a probiotic, has a high survival rate and high colonization ability in the gastrointestinal tract. Tolerance to the gastrointestinal environment and adhesion to intestinal epithelial cells by some Lactobacillus species (excluding L. plantarum) are related to luxS/AI-2. Here, the role of luxS in tolerance to simulated digestive juice (SDJ) and adhesion to Caco-2 cells by L. plantarum KLDS1.0391 (hereafter, KLDS1.0391) was investigated. The KLDS1.0391 luxS mutant strain was constructed by homologous recombination. When luxS was deleted, acid and bile salt tolerance and survival rates in SDJ significantly decreased (p < 0.05 for all). The ability of the luxS deletion strain to adhere to Caco-2 cells was markedly lower than that of the wild-type strain (p < 0.05). The ability of the luxS mutant strain to adhere (competition, exclusion, and displacement) to Escherichia coli ATCC 25922 was significantly lower than that of the wild-type strain (p < 0.05 for all). A significant decrease was noted only in the exclusion adhesion inhibition of the luxS mutant strain to Salmonella typhimurium ATCC 14028 (p < 0.05). These results indicate that the luxS gene plays an important role in the gastrointestinal environment tolerance and adhesion ability of KLDS1.0391.

Bifidobacteria are important mediators of immune system development within the gastrointestinal system and immunological homeostasis. The present study explored the anti-colitic activity of Bifidobacterium bifidum H3-R2 in a murine dextran sulfate sodium (DSS)-induced model of ulcerative colitis (UC). Moreover, this study offers novel insight regarding the molecular basis for the probiotic properties of B. bifidum H3-R2 by analyzing the underlying mechanisms whereby B. bifidum H3-R2-derived proteins affect the intestinal barrier. B. bifidum H3-R2 administration was sufficient to alleviate clinical manifestations consistent with DSS-induced colitis, restoring aberrant inflammatory cytokine production, enhancing tight junction protein expression, and positively impacting overall intestinal microecological homeostasis in these animals. Moreover, the bifidobacteria-derived GroEL and transaldolase (TAL) proteins were found to regulate tight junction protein expression via the NF-κB, myosin light chain kinase (MLCK), RhoA/Rho-associated protein kinase (ROCK), and mitogen-activated protein kinase (MAPK) signaling pathways, preventing the lipopolysaccharide (LPS)-mediated disruption of the intestinal epithelial cell barrier.

Probiotics have long been shown to modulate inflammatory bowel disease (IBD) in a variety of ways, and their major metabolites, short-chain fatty acids (SCFAs), have been shown to have a...

Lactobacillus plantarum is an important industrial lactic acid bacteria, which can be used as a starter culture for fermented milk and meat products. Many Lactobacillus plantarum strains can produce bacteriocins with broad-spectrum antibacterial properties, heat stability, and easy to be hydrolyzed by protease in the process of food fermentation and metabolism, and their potential as biopreservative starter culture in the preservation of fermented food has been recognized. However, the high salt environment in the food matrix can affect bacteriocin production. Hence, the objective of this research is to reveal how salt stress affects the production of bacteriocin and the expression of related genes in this strain by transcriptome sequencing and to further analyze possible regulatory mechanisms, to provide references for the use of bacteriocin as a natural biological preservative in salt-containing foods. The number of viable counts and the antibacterial activity of bacteriocin over the whole growth stages were determined under the stress of 0%, 2%, 3%, 4%, and 6% NaCl. When the strain was cultured at low nanoparticle NaCl concentration (2% or 3%), the growth of the experimental group had no significant difference compared with the control group; however, bacteriocin antibacterial activity increased significantly in the stable phase. When the target strain was cultured under 2% NaCl stress for 24 h, the antimicrobial activity reached the maximum. Subsequently, based on the transcriptome sequencing results obtained by Illumina HiSEq 2500 sequencing system, the differentially expressed genes under 0% and 2% NaCl stress were compared, and the enrichment pathways of these genes were analyzed. A total of 260 genes displayed significant differential expression induced by NaCl: Among them, 159 genes were significantly up-regulated, and 101 genes were down-regulated. Bioinformatic analysis revealed that differentially expressed genes related to bacteriocin synthesis were mainly enriched in bacterial secretion pathway, amino acid synthesis pathway, proteolytic enzyme regulation pathway, purine metabolism pathway, two-component reg- ulation pathway, etc. It is preliminarily speculated that nanoparticle NaCl stress can regulate the synthesis and release of bacteriocin by affecting the expression of secY and ftsY in the cell membrane secretion pathway. We also speculate that nanoparticle NaCl stress can provide raw materials for bacteriocin by affecting the expression levels of genes hisH, cysE, cysM, metB, metA, lysA, and argH in the amino acid synthesis pathway. In addition, our research signified that the expression levels of sat and rpoB in the purine metabolism pathway were up-regulated under nanoparticle NaCl stress, which is beneficial to provide energy for bacteriocin production. The results will be helpful to understand how salt stress regulates bacteriocin synthesis of Lactobacillus plantarum. Furthermore, this study also provides guidance for using bacteriocin-producing strains as biocontrol bacteria in the salt-containing food matrix.