Capacity Of Lactic Acid Bacteria Research Articles

Serine and threonine activate Ser/Thr kinase gene to increase the density of Lactobacillus bulgaricus sp1.1 under salt stress

Salt stress significantly impedes high cell-density culture by suppressing the reproductive capacity of lactic acid bacteria. This study examined the effects of salt stress conditions (2% w/v NaCl) on Lactobacillus bulgaricus sp1.1. Although DNA replication and division ring localization remained unaffected, the down-regulation of the ftsZ and dnaA genes inhibited division ring assembly. Consequently, bacteria exhibited filamentation, increased cell length, and accumulated chromosomes and division rings, which obstructed cell division. Under salt stress, sp1.1 experienced several transcriptional changes. The serine/threonine kinase gene was identified as a significant regulator of bacterial division under salt stress. Exogenous addition of serine and threonine could stimulate the expression of Ser/Thr kinase gene, promote the assembly of division ring, and enhance the dividing ability of the bacterium, which led to a density of 7.93 log CFU/mL under the salt stress, which was 6.92 times higher than that of the untreated group. This study provides a new perspective for high-density cultivation of lactic acid bacteria.

Probiotic capacity of commensal lactic acid bacteria from the intestine of Guinea pigs (Cavia porcellus)

The intricate balance of intestinal microbiota is significantly influenced by the pivotal role of indigenous lactic acid bacteria (LAB). These LAB not only contribute to antimicrobial activity and enhance animal health and productivity but also serve as defense against intestinal infections. In the present study, the probiotic potential of LAB strains isolated from various intestinal sections of adult and young guinea pigs (Cavia porcellus) was comprehensively assessed. Strains belonging to the genera Ligilactobacillus, Weissella, Enterococcus, and Limosilactobacillus were also identified. The antibacterial activities of the LAB strains against Salmonella typhimurium, Escherichia coli, and Staphylococcus aureus were quantified. Exopolysaccharide production, adherence capacity, antibiotic resistance, and bile salt tolerance (0.15 %, 0.30 %, and 0.45 %) of LAB were quantified. Further analyses focused on the effects of pH (2.9, 5.0, 6.4, and 7.4), temperature (40, 50, and 60 °C) and NaCl concentrations (3.5 % and 6.5 % w/v) on LAB growth. Strains GCI9 and GDE10 (Ligilactobacillus salivarius), isolated from the cecum and intestine of guinea pigs, exhibited significant antimicrobial activity against S. typhimurium, E. coli and S. aureus. Remarkable adherence capacity to porcine gastric mucin was demonstrated by L. salivarius strains, specifically ACI1, GCI9, and GDE10, with the highest exopolysaccharide levels produced by ACI1 and GCI9 (1.71 and 1.76 mg/mL, respectively). The probiotic potential was further underscored by remarkable bile salt tolerance, especially in strain GDE10, and substantial exopolysaccharide production. These strains displayed notable adaptability to varying environmental conditions, including NaCl concentrations at 3.5 % and 6.5 %, temperatures ranging from 40 to 60 °C, and pH levels of 2.9, 5.0, 6.4, and 7.4. This comprehensive assessment of the probiotic properties of L. salivarius strains, particularly ACI1, GCI9, and GDE10, shows promise for the development of probiotic formulations aimed at enhancing the intestinal health of guinea pigs.

Lactic acid bacteria (Leuconostoc mesenteroides) as bioprotective agents against some pathogenic fungi in common bean

Abstract The common bean (Phaseolus vulgaris L.) is the most important edible food legume in the world. However, its cultivation encounters several phytopathogens. Our study aims to improve food quality and safety through more natural protection methods such as the use of microorganisms that allows us to avoid and minimize pesticide risks. For this purpose, we tested the antagonistic capacity of lactic acid bacteria isolated from raw goat’s milk against four fungal strains isolated from P. vulgaris var. djedida. In this study, lactic acid bacteria (LAB) (Leuconostoc mesenteroides) were screened in vitro for antifungal activity at 28 °C against Fusarium oxysporum, Botrytis cinerea, Aspergillus flavus, and Alternaria alternata. The statistical analysis of the antifungal activity of LAB showed significant differences after a seven-day period. The results of the direct confrontation on the PDA (Potato Dextrose Agar) and MRS (de Man, Rogosa, and Sharpe) Agar medium showed better inhibition by the lactic acid strain on MRS Agar medium. L. mesenteroides gave the highest inhibition rate of 57.6% for the pathogen B. cinerea and 29.1%, 33.3%, and 26.7%, respectively, for the pathogens A. alternata, B. cinerea, F. oxysporum, and A. flavus on the solid PDA medium. However, on the MRS Agar medium, inhibition rates of 88.1% and 80.5% were observed for the pathogens B. cinerea and A. flavus and a total inhibition of 100% on A. alternata and F. oxysporum in the presence of the strain L. mesenteroides. This study led to suggest that food-derived LAB strains could be selected for biotechnological application to control phytopathogenic fungi.

Characterization of potential probiotic starter cultures of lactic acid bacteria isolated from Ethiopian fermented cereal beverages, Naaqe and Cheka.

To test the in vitro probiotic potential and starter culture capacity of lactic acid bacteria (LAB) isolated from Naaqe and Cheka, cereal-based Ethiopian traditional fermented beverages. 44 strains were isolated from spontaneously fermented Ethiopian cereal-based beverages, Naaqe and Cheka, with 24 putatively identified as LAB and 14 identified up to the species level. The species Limosilactobacillus fermentum (6/12; 50%) and Weissella confusa (5/12, 41.67%) were the predominant species identified from Naaqe, while the two Cheka isolates were Limosilactobacillus fermentum and Pediococcus pentosaceus. Six LAB strains inhibited eight of the nine gastrointestinal indicator key pathogens in Ethiopia, including Escherichia coli, Salmonella enterica subsp. enterica var. Typhimurium, Staphylococcus aureus, Shigella flexneri, and Listeria monocytogenes. Three of the LAB isolates exhibited strain-specific immunostimulation in human monocytes. Based on these probiotic properties and growth, six strains were selected for in situ evaluation in a mock fermentation of Naaqe and Cheka. During primary fermentations, L. fermentum 73B, P. pentosaceus 74D, L. fermentum 44B, Weissella confusa 44D, L. fermentum 82C and Weissella cibaria 83E and their combinations demonstrated higher pH-lowering properties and colony-forming unit counts compared to the control spontaneous fermentation. The same pattern was also observed in the secondary mock fermentation by the Naaqe LAB isolates. In this study, we selected six LAB strains with antipathogenic, immunostimulatory and starter culture potentials that can be used as autochthonous probiotic starters for Naaqe and Cheka fermentations, once their health benefit is ascertained in a clinical trial as a next step.

Exploiting Potential Probiotic Lactic Acid Bacteria Isolated from Chlorella vulgaris Photobioreactors as Promising Vitamin B12 Producers.

Lactic acid bacteria (LAB) have been documented as potential vitamin B12 producers and may constitute an exogenous source of cobalamin for the microalga Chlorella vulgaris, which has been described as being able to perform vitamin uptake. Hence, there is an interest in discovering novel B12-producing probiotic LAB. Therefore, the purpose of the current work was to perform a phenotype-genotype analysis of the vitamin B12 biosynthesis capacity of LAB isolated from C. vulgaris bioreactors, and investigate their probiotic potential. Among the selected strains, Lactococcus lactis E32, Levilactobacillus brevis G31, and Pediococcus pentosaceus L51 demonstrated vitamin B12 biosynthesis capacity, with the latter producing the highest (28.19 ± 2.27 pg mL-1). The genomic analysis confirmed the presence of pivotal genes involved in different steps of the biosynthetic pathway (hemL, cbiT, cobC, and cobD). Notably, P. pentosaceus L51 was the only strain harboring cobA, pduU, and pduV genes, which may provide evidence for the presence of the cobalamin operon. All strains demonstrated the capability to withstand harsh gastrointestinal conditions, although P. pentosaceus L51 was more resilient. The potential for de novo cobalamin biosynthesis and remarkable probiotic features highlighted that P. pentosaceus L51 may be considered the most promising candidate strain for developing high-content vitamin B12 formulations.

Antioxidant Capacity of Lactic Acid Bacteria and Yeasts from Xinjiang Traditional Fermented Dairy Products

(1) Background: The objective of this study was to screen strains with antioxidant potential from lactic acid bacteria (LAB) and yeasts isolated from traditional Xinjiang fermentation products. (2) Methods: Twenty-three strains of LAB and twelve strains of yeast isolated from traditional fermented dairy products from different regions of Xinjiang were selected, and the strains with antioxidant ability were initially screened by measuring the hydroxyl radical scavenging, superoxide anion scavenging, DPPH radical scavenging, ABTS+ radical scavenging, anti-lipid peroxidation, and ferrous ion chelating abilities of their bacterial bodies, cell-free extracts, and fermentation broth. They were further screened by measuring their superoxide dismutase (SOD), glutathione peroxidase (GPX), and catalase (CAT) activities to identify strains with more powerful oxidative abilities. (3) Results: The results show that Lacticaseibacillus paracasei NM-12, Enterococcus faecium UM-12 and NM-11, and Pichia fermentans QY-4 had effective antioxidant enzyme activities. The SOD activity of these strains reached 4.846 ± 0.21 U/mL, 9.105 ± 0.428 U/mL, 8.724 ± 0.365 U/mL, and 6.518 ± 0.223 U/mL; the GPX activity reached 0.1396 ± 0.009 U/mL, 0.1123 ± 0.006 U/mL, 0.014 ± 0.007 U/m, and 0.0919 ± 0.006 U/mL; and the CAT activity reached 19.934 ± 3.072 U/mL, 3.749 ± 0.926 U/mL, 92.095 ± 1.017 U/mL, and 97.289 ± 0.535 U/mL, respectively (p < 0.05). (4) Conclusions: Lacticaseibacillus paracasei (NM-11), Enterococcus faecium (UM-12, NM-11), and Pichia fermentans (QY-4), isolated from traditional fermented dairy products, are probiotics with high antioxidant activity and potential applications in the food and fermentation industries.

Effect of probiotic Bacillus cereus DM423 on the flavor formation of fermented sausage

Insufficient protein and fat hydrolysis capacity of lactic acid bacteria (LAB) limit the flavor formation of fermented sausage. Bacillus is known for its substantial expression of proteases and lipases. However, its application in meat fermentation remains underexplored. In this study, a strain of probiotic Bacillus cereus (B. cereus DM423) was employed as a co-starter to improve the quality of Lactiplantibacillus plantarum (L. plantarum HH-LP56) fermented sausage. The addition of DM423 did not interfere with regular fermentation, but it significantly improved the flavor, as measured by electronic tongue and electronic nose. Further analyses using SDS-PAGE and thin-layer chromatography observed enhanced hydrolysis of protein and fat in sausages in which DM423 was involved in fermentation. GC-IMS identified DM423 mediated upregulation of various flavor compounds, including esters, ketones, furans, and branched-chain fatty acids. In addition, genomic de novo sequencing revealed that DM423 carried an abundance of genes associated with proteolysis, lipolysis, and the production of flavor substances, whereas HH-LP56 lacked these genes. Overall, this study finds that B. cereus DM423 can promote flavor formation in fermented sausages. It may illuminate a promising direction for the development of sausage co-starters from a wider microbial pool.

Uncovering the specificity and predictability of tryptophan metabolism in lactic acid bacteria with genomics and metabolomics.

Tryptophan is metabolized by microorganisms into various indole derivatives that have been proven to alleviate diseases and promote human health. Lactic acid bacteria (LAB) are a broad microbial concept, some of which have been developed as probiotics. However, the capacity of most LAB to metabolize tryptophan is unknown. In this study, the aim is to reveal the rule of tryptophan metabolism in LAB by multi-omics. The findings showed that LAB were rich in genes for tryptophan catabolism and that multiple genes were shared among LAB species. Although the number of their homologous sequences was different, they could still form the same metabolic enzyme system. The metabolomic analysis revealed that LAB were capable of producing a variety of metabolites. Strains belonging to the same species can produce the same metabolites and have similar yields. A few strains showed strain-specificity in the production of indole-3-lactic acid (ILA), indole-3-acetic acid, and 3-indolealdehyde (IAld). In the genotype-phenotype association analysis, the metabolites of LAB were found to be highly consistent with the outcomes of gene prediction, particularly ILA, indole-3-propionic acid, and indole-3-pyruvic acid. The overall prediction accuracy was more than 87% on average, which indicated the predictability of tryptophan metabolites of LAB. Additionally, genes influenced the concentration of metabolites. The levels of ILA and IAld were significantly correlated with the numbers of aromatic amino acid aminotransferase and amidase, respectively. The unique indolelactate dehydrogenase in Ligilactobacillus salivarius was the primary factor contributing to its large production of ILA. In summary, we demonstrated the gene distribution and production level of tryptophan metabolism in LAB and explored the correlation between genes and phenotypes. The predictability and specificity of the tryptophan metabolites in LAB were proven. These results provide a novel genomic method for the discovery of LAB with tryptophan metabolism potential and offer experimental data for probiotics that produce specific tryptophan metabolites.

Exploring the binding capacity of lactic acid bacteria derived bacteriocins against RBD of SARS-CoV-2 Omicron variant by molecular simulations

The changes in the SARS-CoV-2 genome have resulted in the emergence of new variants. Some of the variants have been classified as variants of concern (VOC). These strains have higher transmission rate and improved fitness. One of the prevalent were the Omicron variant. Unlike previous VOCs, the Omicron possesses fifteen mutations on the spike protein's receptor binding domain (RBD). The modifications of spike protein's key amino acid residues facilitate the virus' binding capability against ACE2, resulting in an increase in the infectiousness of Omicron variant. Consequently, investigating the prevention and treatment of the Omicron variant is crucial. In the present study, we aim to explore the binding capacity of twenty-two bacteriocins derived from Lactic Acid Bacteria (LAB) against the Omicron variant by using protein-peptidedocking and molecular dynamics (MD) simulations. The Omicron variant RBD was prepared by introducing fifteen mutations using PyMol. The protein-peptide complexes were obtained using HADDOCK v2.4 docking webserver. Top scoring complexes obtained from HADDOCK webserver were retrieved and submitted to the PRODIGY server for the prediction of binding energies. RBD-bacteriocin complexes were subjected to MD simulations. We discovered promising peptide-based therapeutic candidates for the inhibition of Omicron variant for example Salivaricin B, Pediocin PA 1, Plantaricin W, Lactococcin mmfii and Enterocin A. The lead bacteriocins, except Enterocin A, are biosynthesized by food-grade lactic acid bacteria. Our study puts forth a preliminary information regarding potential utilization of food-grade LAB-derived bacteriocins, particularly Salivaricin B and Pediocin PA 1, for Covid-19 treatment and prophylaxis. Communicated by Ramaswamy H. Sarma

Factors affecting selenium-enrichment efficiency, metabolic mechanisms and physiological functions of selenium-enriched lactic acid bacteria

• Summarize the factors affecting the Se enrichment capacity of Se-enriched LABs. • Discuss the metabolic mechanisms and physiological functions of Se-enriched LABs. • Conclude the applications of selenium-enriched LABs in food production. Selenium (Se)-enriched lactic acid bacteria (LAB) are live bacteria preparations that accumulate and bio-transform inorganic Se into organic Se forms including Se-nanoparticles (SeNPs), Se-amino acids and selenoproteins. Se-enriched LAB can play the dual role of organic Se supplement and probiotic effects, and have great applications in the food and biomedical fields. Therefore, more and more attentions have been paid on the Se-enriched LAB. This paper firstly summarized the factors affecting the Se-enrichment efficiency of Se-enriched LAB, then discussed the metabolic mechanisms and physiological functions of Se-enriched LAB, and finally reviewed their applications in food production, in order to provide a guidance for the theoretical and practical implementation of Se-enriched LAB. We concluded that 1) both biomass and the amount of Se enrichment should be used as dual indicators to screen Se-enriched LAB and comprehensively optimize the influencing factors including initial Se concentration, pH, inoculation amount, species of LAB to ensure the Se enrichment efficiency. 2) The metabolic mechanism underlining Se-enriched LAB needs to be further revealed, which will facilitate the production of higher value Se compounds by LAB. 3) The proven physiological functions of Se-enriched LAB include 5 categories: antioxidant activity, antibacterial activity, improving the physical function of animals, detoxification and disease prevention. However, the application of Se-enriched LAB in medical field currently still lacks clinical research, and convincing clinical evidence of effectiveness for Se-enriched LAB on human being must be established. 4) The application in the food field will benefit from the stable existence in the food system of Se-enriched LAB and public acceptance, which come before the various health benefits. In any case, the great potential value of Se-enriched LAB formulations deserves further comprehensive exploration and development.

Potential allergenicity and hydrolysis assessment of bovine casein and β-casein by treatment with lactic acid bacteria.

Casein is one of the main allergens in cow's milk, accounting for 80% of cow's milk proteins. The ability of hydrolyzing proteins by bacteria is also different. In this study, the capacity of lactic acid bacteria to hydrolyze casein or β-casein and the IgG/IgE-binding capacity of hydrolysates were evaluated. The intensity of casein and β-casein degradation was analyzed by SDS-PAGE and RP-HPLC. The hydrolysates were tested for their capacity to inhibit IgG and IgE binding by ELISA. The peptides in the hydrolysate were also analyzed by LC-MS/MS. In these strains, Lactobacillus rhamnosus (CICC No. 22175) had the strongest hydrolysis of casein and β-casein. The hydrolysate of Lactobacillus rhamnosus (CICC No. 22175) showed the lowest antigenicity and potential allergenicity. It also hydrolyzed major allergen IgE epitopes and preserved T cell epitopes. Thereore Lactobacillus rhamnosus (CICC No. 22175) could be used for developing hypoallergenic dairy products and the development of tolerance. PRACTICAL APPLICATIONS: By the study, it obtained that a strain of Lactobacillus rhamnosus could effectively degrade casein and reduced the potential allergenicity of casein. At the same time, some major allergic epitopes were hydrolyzed and T cell epitopes were preserved. Therefore, it is very valuable for the application and development of lactic acid bacteria. The hydrolysate can also be used in a new hypoallergenic dairy formula with specific health benefits and promoting oral tolerance.

Capabilities of bio-binding, antioxidant and intestinal environmental repair jointly determine the ability of lactic acid bacteria to mitigate perfluorooctane sulfonate toxicity.

Perfluorooctane sulfonate (PFOS) is a novel environmental contaminant that can be enriched in humans through the food chain, causing liver diseases, neurotoxicity and metabolic disorders. Lactic acid bacteria (LAB) are safe food-grade microorganisms that exhibit high antioxidant activity and bio-binding capacity towards toxins. Here, strains of LAB with different PFOS binding capacities and antioxidant activities were selected and analyzed for their ability in mitigating the toxic effects of PFOS. The results showed that the PFOS binding capacity and antioxidant activity of LAB largely influenced their ability in alleviating the toxic effects of PFOS. Notably, the individual LAB strains with low PFOS binding capacities and antioxidant activities also attenuated the toxic effects of PFOS, which was shown to up-regulate the contents of short-chain fatty acids (SCFAs) in the cecum and of tight junction proteins in the intestines of mice. Therefore, the mitigation pathway of PFOS-induced toxic damage by LAB is not limited to bio-binding and antioxidant. Repairing the gut environment damaged by PFOS is also essential for LAB to alleviate the toxic damage due to PFOS and may be partly independent of the bio-binding and antioxidant. Therefore, LAB as an alternative pathway for alleviating PFOS toxicity is suggested.

Lactic acid bacteria alleviate di-(2-ethylhexyl) phthalate-induced liver and testis toxicity via their bio-binding capacity, antioxidant capacity and regulation of the gut microbiota

Di-(2-ethylhexyl) phthalate (DEHP) is a plasticiser that, if absorbed into the human body, can cause various adverse effects including reproductive toxicity, liver toxicity and gut microbiota dysbiosis. So far, some studies have proved that the toxicity of DEHP can be reduced by using antioxidants. However, these candidates all show potential side effects and cannot prevent the accumulation of DEHP in the body, making them unable to be used as a daily dietary supplement to relieve the toxic effects of DEHP. Lactic acid bacteria (LAB) have antioxidant capacity and the ability to adsorb harmful substances. Herein, we investigated the protective effects of five strains of LAB, selected based on our in vitro assessments on antioxidant capacities or bio-binding capacities, against the adverse effects of DEHP exposure in rats. Our results showed that LAB strains with outstanding DEHP/MEHP binding capacities, Lactococcus lactis subsp. lactis CCFM1018 and Lactobacillus plantarum CCFM1019, possess the ability to facilitate the elimination of DEHP and its metabolite mono-(2-ethylhexyl) phthalate (MEHP) with the faeces, decrease DEHP and MEHP level in serum further. Meanwhile, DEHP-induced liver and testicular injuries were effectively alleviated by CCFM1018 and CCFM1019. In addition, CCFM1018 effectively alleviated the DEHP-induced oxidative stress with its strong antioxidant ability. Furthermore, both CCFM1018 and CCFM1019 modulated the gut microbiota, which in turn increased the concentrations of faecal propionate and butyrate and regulated the pathways related to host metabolism. Correlation analysis indicate that DEHP/MEHP bio-binding capacity of LAB plays a crucial role in protecting the body from DEHP exposure, and its antioxidant capacity and the ability to alleviate the gut microbiota dysbiosis are also involved in the alleviation of damage. Thus, LAB with powerful bio-binding capacity of DEHP and MEHP can be considered as a potential therapeutic dietary strategy against DEHP exposure.

Screening of mixed lactic acid bacteria starter and its effects on the quality and flavor compounds of fermented Lentinus edodes

The lactic acid bacteria (LAB) with excellent fermented performance were screened for Lentinus edodes fermentation by measuring the growth status and acid producing capacity of different LAB in L. edodes, and the optimal mixed ratio of LAB was selected for the L. edodes fermentation through the mixed fermented test. Factors affecting the quality of fermented L. edodes were optimized by single factor experiment and response surface experiment. The results showed that when the mixed ratio of LAB was Lactobacillus delbrueckii subsp. bulgaricus: Lactiplantibacillus plantarum: Lacticaseibacillus rhamnous = 3:1:2, fermented L. edodes had the best fermented quality. The optimized process parameters of mixed LAB fermented L. edodes were as follows: fermentation temperature of 37 °C, salt content of 1%, and inoculation amount of 2.7%. Under this process, the total acid and sensory score of fermented L. edodes were 0.88 g/100 g and 81.7 points, respectively. Compared with the unfermented L. edodes, the contents of acids and ketones in the fermented L. edodes increased by 2.16% and 17.8%, while the contents of alcohols, aldehydes and phenols were relatively reduced by 3.66%, 7.42%, and 3.87%, respectively. This study provides a theoretical basis for the development of LAB fermented food of L. edodes.

The state of water is associated with the viability and acidification capacity of Lactobacilli in frozen sourdough

The correlations between water state and the key factors affecting sourdough quality, including cell activity and acidification capacity of lactic acid bacteria (LAB), were established in this study. Results revealed that with the increase of frozen storage time, the cell density (CD), total titratable acidity (TTA), and organic acids content declined, whereas the pH value rose. Further, the freezable water content (FWC) and free water quantity (FWQ) decreased, but the total water loss rate (WLR) and immobilised water quantity (IWQ) increased. The CD showed a highly inversely correlation with WLR, and the pH value was strongly inversely correlated to the FWQ. The confocal laser scanning microscopy (CLSM) observed that the ice crystals had larger volumes during frozen storage. Our data, for the first time, disclosed that the total water content and the FWQ may play a crucial role in maintaining the viability and acidification capacity of LAB in frozen sourdough.

ADHESION FACTORS OF LACTIC ACID BACTERIA AND BIFIDOBACTERIA

The review presents data on adhesive and biofilm-generating capacity of lactic acid bacteria and bifidobacteria, promoting microbial colonization of gastrointestinal tract and their application as constituents of probiotics. The structural elements 
 involved in adhesion include pili-like formations, cell surface proteins (adhesins, S-layer proteins, moonlighting proteins), exopolysaccharides, lipoteichoic and teichoic acids. Methods of studying the adhesive properties of bacteria and the main 
 environmental factors affecting the expression of genes engaged in the mechanism of adhesion have been considered.

Capacity of soybean carbohydrate metabolism in Leuconostoc mesenteroides, Lactococcus lactis and Streptococcus thermophilus

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 lactis and Streptococcus thermophilus were 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, scrK and scrR. Among the 15 strains, only 1 L. lactis strain possessed both sucrose permease and PTS pathway. On the other hand, only Leu. mesenteroides among the 3 species have the genes related to α-galactosidases for potential capacity to metabolize raffinose-family oligosaccharides (RFO) in soybean. Four Leu. mesenteroides strains, DQHXN_Q03M16, FSDLZ60M2, DSCAB2M6 and DQHXN_Q38M5, possessed the complete α-galactosidases gene clusters of lacS-galA-galK-galT and 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. lactis and S. thermophilus in soybean carbohydrate metabolism for suitable strain selection in soybean fermentation.

Recent Advances in Lactic Acid Production by Lactic Acid Bacteria.

Lactic acid can synthesize high value-added chemicals such as poly lactic acid. In order to further minimize the cost of lactic acid production, some effective strategies (e.g., effective mutagenesis and metabolic engineering) have been applied to increase productive capacity of lactic acid bacteria. In addition, low-cost cheap raw materials (e.g., cheap carbon source and cheap nitrogen source) are also used to reduce the cost of lactic acid production. In this review, we summarized the recent developments in lactic acid production, including efficient strain modification technology (high-efficiency mutagenesis means, adaptive laboratory evolution, and metabolic engineering), the use of low-cost cheap raw materials, and also discussed the future prospects of this field, which could promote the development of lactic acid industry.

Lactic acid bacteria alleviate liver damage caused by perfluorooctanoic acid exposure via antioxidant capacity, biosorption capacity and gut microbiota regulation

Perfluorooctanoic acid (PFOA) is an environmental pollutant that has multiple toxic effects. Although some medicines and functional food ingredients are currently being used to alleviate the biological toxicity effects caused by PFOA, these candidates all show potential side effects and cannot prevent the accumulation of PFOA in the body, making them unable to be used as a daily dietary supplement to relieve the toxic effects of PFOA. However, new research has shown that lactic acid bacteria (LAB) can alleviate toxicity caused by exposure to foreign substances. In this study, multiple strains of LAB with different adsorption capacities or antioxidant capacities were used to analyse their mitigation effects of on liver damage caused by PFOA exposure. The results showed that the adsorption capacity and antioxidant capacity of LAB could alleviate the liver toxicity of PFOA to a certain extent. Moreover, treatment with some strains of LAB was able to recover the gut microbiota dysbiosis caused by PFOA exposure, such as by increasing the relative abundances of Patescibacteria, Proteobacteria, Akkermansia and Alistipes or decreasing the abundances of Bacteroides and Blautia. In addition, a strain with neither outstanding antioxidant capacity nor adsorption capacity also reversed the decline in short-chain fatty acid levels caused by PFOA exposure. The ability of these strains to relieve gut microbiota dysbiosis partly explains the inconsistency between the capacity for antioxidant or PFOA adsorption and the ability of the strains to alleviate PFOA toxicity. The results indicate that the PFOA adsorption capacity and antioxidant capacity of LAB may be involved in the alleviation of PFOA liver toxicity. In addition, LAB could also alleviate liver damage caused by PFOA by adjusting the gut microbiota and short-chain fatty acid content. Therefore, some strains of LAB can be used as a potentially safe dietary supplement to relieve PFOA-induced liver damage.

Lactic acid bacterial exopolysaccharides strongly bind histamine and can potentially be used to remove histamine contamination in food.

The symptoms of foodborne histamine poisoning are similar to those of IgE-mediated food allergies. In this study, we investigated the histamine-binding capacity of lactic acid bacteria (LAB) strains as potential preventive agents against histamine poisoning. Histamine biosorption capacity was determined for 16 LAB strains. Leuconostoc mesenteroides TOKAI 51 m, Lactobacillus paracasei TOKAI 65 m, Lactobacillus plantarum TOKAI 111 m and Pediococcus pentosaceus TOKAI 759 m showed especially high biosorption rates and reached saturation within 30 min. Adsorption isotherms showed better conformance to the Freundlich model than to the Langmuir model. Analyses after heat, periodic acid and guanidine hydrochloride treatments suggested that histamine was bound to the bacterial cell surface. HPLC analysis revealed that exopolysaccharides produced by Lact. paracasei TOKAI 65 m strongly bound to histamine. In the detachment test with 1 mol l-1 HCl solution, the dissociation rate of histamine for Lact. paracasei TOKAI 65 m was <10 %. This strain is presumably a suitable candidate for use against histamine poisoning.