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Bacteriocins are a class of anti-microbial proteins or peptides produced by bacteria that have antimicrobial activity and are regarded as potential alternatives to antibiotics. Lactobacillus(L.) gasseri, which is a probiotic, can produce bacteriocins. In the present study, we determined the bacteriostatic ability and bacteriocin-producing species of four strains of L. gasseriand investigated the effects of gavage of different bacteriocin-producing L. gasseri, on serum biochemical indices, intestinal cytokines, and gut microbiota of normal mice, a total of 40 C57BL/6J mice were used in the above study, where the gavage L. gasserigroup was given a dose of 109 CFU/d. The ability of different bacteriocin-producing L. gasseri, to alleviate the symptoms caused by Salmonella(S.) typhimuriuminfection was further investigated, and the key bacteriocins and potential mechanisms were discuss, a total of 48 C57BL/6J mice were used in the above study.The results showed that Helveticin J, Gassericin K7B, Acidocin B and Bacteriocin LS2-producing L. gasseriFJXPY47L6, and FGSYC2L2, and FHNFQ28L4 could significantly improve the symptoms caused by S. typhimuriuminfection, and the bacteriocin-producing L. gasseriFJXPY47L6, and FGSYC2L2. Bacteriocin LS2-producing FJXPY47L6 showed the greatest ability to alleviate symptoms caused by S. typhimuriuminfection. These effects are achieved through bacteriocin-producing modulation of intestinal cytokines, gut microbiota, and short-chain fatty acids.

There has been a rising interest in studying how Bifidobacterium brevecan affect the immune system over the years. The aim of this study was to evaluate the effect of B. breveon the immune system and to explore the mechanism in a mouse model of cyclophosphamide (CTX)-induced immunosuppression. The results of the study showed that B. breveCCFM1310 significantly increased the thymus index (p < 0.05), promoting the secretion of immunoglobulins and the number of immune cells in the blood. Moreover, B. breveCCFM1310 could repair the spleen injury. It increased the mRNA expression level of T-bet (p < 0.05) and decreased the mRNA expression level of TGF-β and FOXP3 (p < 0.05). B. breveCCFM1310 alleviated oxidative stress by increasing enzymatic activities of SOD, CAT and T-AOC and reducing the concentration of MDA. Moreover, it repaired intestinal damage by increasing the number of goblet cells, upregulating mRNA expression of tight junction proteins, and promoting the production of short-chain fatty acids (SCFA). B. breveCCFM1310 could regulate the gut microbiota by increasing the relative abundance of Lactobacillus(p < 0.05) and decreasing the relative abudance of LachnospiraceaeNK4A136 group. Overall, our study suggests that B. breveCCFM1310 could enhance immunity in CTX-induced immunosuppressed mice by affecting immune responses, oxidative stress and gut microbiota.

Previous studies indicated that Limosilactobacillus mucosaehad a good ability to regulate lipid metabolism, however, there was limited research on its safety. In this study, we assessed the safety of three L. mucosaestrains including genotypes and phenotype, subacute oral toxicity test, and their influences on immunosuppressed mice. The results showed that there were no virulence genes or genetic islands with clear pathogenicity in the genomes of L. mucosaeDCC1HL5, FZJTZ26M3, and GD16M9. All three strains were resistant to chloramphenicol, additionally, DCC1HL5 was resistant to kanamycin and tetracycline, but the possibility of horizontal transfer of their resistance genes was relatively low. L. mucosaeDCC1HL5, FZJTZ26M3, and GD16M9 did not produce biogenic amine, and α-hemolysis was found. The results of the 28-day subacute oral toxicity test showed that 109 CFU of each strain did not cause significant abnormalities in various aspects such as body weight, organ indexes, histopathology, hematological parameters, fasting blood glucose, serum lipids, liver parameters, and intestinal inflammation in both healthy and immunosuppressed mice. Therefore, L. mucosaeDCC1HL5, FZJTZ26M3, and GD16M9 have the potential for safe application in functional foods.

Streptococcus thermophilusis generally considered to be sensitive to bile salt stimulation, and its bile salt tolerance is strain specific. In this study, the viable bacteria count, sugar utilization capacity, β-galactosidase activity, and extracellular polysaccharide synthesis capacity of 5 strains of Streptococcus thermophilusin bile salt with or without (w/o) lactose were measured to explore the protective ability of lactose to the strains. The changes in gene expression in stress and carbohydrate metabolism-related pathways were recorded. The results indicated that the protective effect of lactose on the bile salt stress response of Streptococcus thermophilusis strain dependent. The β-galactosidase activity of the strains was correlated with the yield of exopolysaccharides (EPS) significantly, and the strain with a high survival rate (4M6) showed higher lactose utilization, β-galactosidase activity and more EPS production in general.

Lactococcus lactissubsp. lactisis a common starter culture in the dairy industry. In this study, the key pathway of five strains of Lactococcus lactissubsp. Lactisregarding their fermentation characteristics in milk systems were studied by metabolomic approach, fermentation characterization and sensory evaluation. Strains DSCAB11M15 and DYNDL21-2, which express the cell wall proteinase PrtM/P, exhibited rapid proliferation and acidification, with significant differences in volatile and non-volatile metabolites including upregulation of flavor compounds such as ethyl butyrate and 2,3-butanedione. Additionally, DYNDL21-2, which carries the α-ketoacid decarboxylase gene, significantly increased the content of 3-methyl-butyric aldehyde, a compound that imparts a caramel-like flavor, in fermented milk. This study offers guidance for the comprehensive investigation of starter cultures with multiple approaches.

Lactobacillus helveticusstrains are used as starter cultures in the manufacture of fermented milk products. Its growth relies on a complex proteolytic system that includes cell-envelope proteinases and peptidases. The proteolytic systems of only a few strains of L. helveticusin terms of genotype and phenotype have been previously characterized. A phylogenetic configuration, pan/core genome analysis and evaluation of the proteolytic enzymatic activities were done for 50 strains of L. helveticusincluding 38 isolated in the laboratory and derived from various ecological niches. While the genome sizes ranged from 1.80 to 2.26 Mbp, diversity in aminopeptidase activities was observed among the L. helveticusstrains. This study helped show the genetic and phenotypic diversity of L. helveticusisolated from various environments and their potential application in fermented dairy products. More analysis is necessary to better understand the influence of genetic and phenotypic diversity of L. helveticuson its activity in food.

Few studies have focused on the capacity of lactic acid bacteria in utilizing soybean carbohydrates by genetic and phenotypic approaches. In the current study, genetic and phenotypic characteristics of soybean carbohydrate metabolism in Leuconostoc mesenteroides, Lactococcus lactisand Streptococcus thermophiluswere investigated. The results indicated that all the 3 species have the potential capacity to utilize sucrose with a sucrose phosphoenolpyruvate-dependent phosphotransferase system (PTS) pathway mainly consisted of scrA, sacA, scrKand scrR.Among the 15 strains, only 1 L. lactisstrain possessed both sucrose permease and PTS pathway. On the other hand, only Leu. mesenteroidesamong the 3 species have the genes related to α-galactosidases for potential capacity to metabolize raffinose-family oligosaccharides (RFO) in soybean. Four Leu. mesenteroidesstrains, DQHXN_Q03M16, FSDLZ60M2, DSCAB2M6 and DQHXN_Q38M5, possessed the complete α-galactosidases gene clusters of lacS-galA-galK-galTand high α-galactosidases activity, which contributed to the capacity of these strains to utilize RFO. These findings provide an approach to investigate the genetic and the phenotypic characteristics of Leu. mesenteroides, L. lactisand S. thermophilusin soybean carbohydrate metabolism for suitable strain selection in soybean fermentation.