Optimization of bacteriocin production by Lactobacillus acidophilus AA11, a strain isolated from Egyptian cheese

Evaluation of Different Nutritional Sources in Lactic Acid Bacteria Fermentation for Sustainable Postbiotic Production

In recent years, interest in postbiotics has grown due to their potential health benefits and applications in food systems. This study evaluated various nutritional sources for lactic acid bacteria (LAB) fermentation to enhance postbiotic production. Three LAB strains were tested: Pediococcus acidilactici CECT 9879 (PA), Weissella cibaria CECT 30731 (WC), and Lactococcus lactis CECT 30734 (LL). Fermentation experiments assessed bacterial growth, pH levels, and antibacterial activity against E. coli using different carbon and nitrogen sources. Fructose and xylose significantly improved growth in WC (9.39 ± 0.16 log CFU/mL) and LL (9.37 ± 0.22 log CFU/mL) compared to glucose. Ribose enhanced antimicrobial activity in PA (41.67 ± 2.89%) and WC (50.00 ± 0.00%) relative to glucose. Additionally, plant-based nitrogen sources, such as soy (LL: 8.93 ± 0.12 log CFU/mL and 81.67 ± 2.89%) and wheat (WC: 9.40 ± 0.17 log CFU/mL and 65.00 ± 0.00%), along with microbial sources like yeast (PA: 9.57 ± 0.12 log CFU/mL and 40.00 ± 0.00%), effectively supported growth and antibacterial activity. These findings highlight the potential of developing animal-free fermentation media that meet nutritional, safety, and sustainability criteria while making a significant contribution to the optimization of postbiotic production.

Optimization of Culture Medium Ingredients and Culture Conditions for Bacteriocin Production in Lactococcus lactis NCU036019

Bacteriocin lactococcin036019 was identified and characterized from Lactococcus lactis NCU036019, which displayed significant antibacterial activity toward foodborne pathogenic bacteria Staphylococcus aureus under various conditions. However, the in situ low-level expression of lactococcin036019 severely limited its wide application in food industry. In this study, we optimized the medium ingredients and culture conditions of L. lactis NCU036019 for maximum production of lactococcin036019. The effects of different carbon sources, nitrogen sources, inorganic salts, growth factors, surfactants, and buffer salts on the production of bacteriocin were studied using antibacterial titer and diameter of inhibitory zone as evaluation indexes. Through single-factor experiments, Plackett-Burman (PB) experiment, steepest ascent experiment and response surface methodology, yeast extract, zinc sulfate, sodium acetate, mannitol, Tween-80, and dipotassium hydrogen phosphate were identified to display significant influence on the production of bacteriocin. By optimizing Man Rogosa and Sharpe (MRS) culture medium ingredients, the antibacterial activity of lactococcin036019 in the cell-free supernatant raised from 46.19 to 300.14 Au/mL, namely, 6.5 times increased. Furthermore, the culture conditions, such as inoculation amount, culture time, and culture temperature, were optimized, and this further increased the antibacterial activity to 409 Au/mL, namely, 8.8 times increased. This study investigated the effects of culture media and conditions on the production of lactococcin036019, and they were optimized for a maximum harvest of bacteriocin, and the significant increase of bacteriocin production in L. lactis NCU036019 facilitates the application of the antibacterial substance in future work.

Antibacterial Activity and Cytotoxicity of the Novel Bacteriocin Pkmh

Bacteriocins are a class of proteins produced by bacteria that are toxic to other bacteria. These bacteriocins play a role in bacterial competition by helping to inhibit potential competitors. In this study, we isolated and purified a novel bacteriocin Pkmh, different from the previously reported bacteriocin PA166, from Pseudomonas sp. strain 166 by ammonium sulfate precipitation, dialysis membrane method, ion exchange chromatography, and gel filtration chromatography. SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) revealed that the molecular weight of Pkmh is approximately 35 kDa. Pkmh exhibited potent antimicrobial activity against bovine Mannheimia haemolytica (M. haemolytica) with low cytotoxicity, and lower hemolytic activity was observed. In addition, Pkmh retained antimicrobial activity at different pH ranges (2-10) and temperature conditions (40, 60, 80, 100 °C). Our analysis of its antimicrobial mechanism showed that Pkmh acts on bacterial cell membranes, increasing their permeability and leading to cell membrane rupture and death. In conclusion, Pkmh exhibited low hemolytic activity, low toxicity, and potent antibacterial effects, suggesting its potential as a promising candidate for clinical therapeutic drugs.

Factors affecting production and effectiveness, performance improvement and mechanisms of action of bacteriocins as food preservative

Modern society is increasingly attracted with safe, natural, and additive-free food products, that gives preference to bacteriocins produced by General Recognized as Safe bacteria as a food preservative. Bacteriocins have been reported to be effective in extending shelf life of diverse foods such as meats, dairy products, wine, juice, and fruits and vegetables, whereas commercialized bacteriocins remain only nisin, pediocin, and Micocin. It is important that commercialized preservatives undergo an easy-to-handle manufacturing while maintaining high efficacy. Limited application of bacteriocins is most often caused by the absence of legislatives for use, low production, high cost and complicated purification process, reduced efficiency in the complex food matrix and insufficiently defined mechanism of action. Accordingly, this review provides an overview of bacteriocins, in relation to production stimulation, general purification scheme, impact of food matrix on bacteriocin effectiveness, and collaborative technology to improve bacteriocin performances. It is worth to note that purification and performance improvement technology remain the two challenging tasks in promoting bacteriocins as a widely used bio-preservative. Furthermore, this review for the first time divides bacteriocin receptors into specific classes (class I, II, III) and nonspecific class, to provide a basis for an in-depth understanding of the mechanism of action.

Evaluation of Rye Bran Enzymatic Hydrolysate Effect on Gene Expression and Bacteriocinogenic Activity of Lactic Acid Bacteria

Lactic acid bacteria (LAB) bacteriocins can be considered as a bio-preservatives and an alternative to antibiotics, but the high manufacturing costs limit their commercial application. The screening of LAB strains for bacteriocinogenic activity was carried out and the effect of rye bran enzymatic hydrolysate (RBEH) on gene expression and bacteriocin production was evaluated. qPCR and RT-PCR was applied for bacteriocin gene detection and their expression quantification. The agar diffusion technique with the test strains of Bacillus spp., Staphylococcus spp. and Salmonella enterica was performed for antimicrobial activity assessment of LAB cultivated in MRS broth and RBEH (processed with proteases and cellulases). The genes of different bacteriocins were revealed for thirteen out of eighteen LAB strains, while the antimicrobial activity was detected only for four of them. The strains of Lactobacillus paracasei VKPM B-11657 and L. salivarius VKPM B-2214 with unnamed class IIb bacteriocin gene demonstrated the widest spectrum of activity. The growth patterns and bacteriocin gene expression differed between both strains and media. The activity of cell-free supernatants after cultivation in RBEH was slightly lower. However, the test strain of S. epidermidis was inhibited by L. paracasei cultivated in RBEH but not in MRS. Thus, rye bran can be applied as a sole source of nutrients for LAB fermentation and bacteriocin production.

Biorefinery of Brewery Spent Grain by Solid-State Fermentation and Ionic Liquids

Novel environmentally friendly pretreatments have been developed in recent years to improve biomass fractionation. Solid-state fermentation (SSF) and treatment with ionic liquids show low environmental impact and can be used in biorefinery of biomass. In this work, these processes were assessed with brewery spent grain (BSG). First, BSG was used as a substrate to produce cellulases and xylanases by SSF with the fungi Aspergillus brasiliensis CECT 2700 and Trichoderma reesei CECT 2414. Then, BSG was pretreated with the ionic liquid [N₁₁₁₂OH][Gly] and hydrolyzed with the crude enzymatic extracts. Results showed that SSF of BSG with A. brasiliensis achieved the highest enzyme production; meanwhile, the pretreatment with ionic liquids allowed glucan and xylan fractions to increase and reduce the lignin content. In addition, a mixture of the extracts from both fungi in a ratio of 2.5:0.5 Aspergillus/Trichoderma (v/v) efficiently hydrolyzed the BSG previously treated with the ionic liquid [N₁₁₁₂OH][Gly], reaching saccharification percentages of 80.68%, 54.29%, and 19.58% for glucan, xylan, and arabinan, respectively. In conclusion, the results demonstrated that the BSG biorefinery process developed in this work is an effective way to obtain fermentable sugar-containing solutions, which can be used to produce value-added products.

Biosynthesis and Production of Class II Bacteriocins of Food-Associated Lactic Acid Bacteria

Bacteriocins are ribosomally synthesized peptides made by bacteria that inhibit the growth of similar or closely related bacterial strains. Class II bacteriocins are a class of bacteriocins that are heat-resistant and do not undergo extensive posttranslational modification. In lactic acid bacteria (LAB), class II bacteriocins are widely distributed, and some of them have been successfully applied as food preservatives or antibiotic alternatives. Class II bacteriocins can be further divided into four subcategories. In the same subcategory, variations were observed in terms of amino acid identity, peptide length, pI, etc. The production of class II bacteriocin is controlled by a dedicated gene cluster located in the plasmid or chromosome. Besides the pre-bacteriocin encoding gene, the gene cluster generally includes various combinations of immunity, transportation, and regulatory genes. Among class II bacteriocin-producing LAB, some strains/species showed low yield. A multitude of fermentation factors including medium composition, temperature, and pH have a strong influence on bacteriocin production which is usually strain-specific. Consequently, scientists are motivated to develop high-yielding strains through the genetic engineering approach. Thus, this review aims to present and discuss the distribution, sequence characteristics, as well as biosynthesis of class II bacteriocins of LAB. Moreover, the integration of modern biotechnology and genetics with conventional fermentation technology to improve bacteriocin production will also be discussed in this review.

Optimization of food-grade medium for co-production of bioactive substances by Lactobacillus acidophilus LA-5 for explaining pharmabiotic mechanisms of probiotic

This study aimed to optimize the co-production of conjugated linoleic acid (CLA), exopolysaccharides (EPSs) and bacteriocins (BACs) by Lactobacillus acidophilus LA-5 in dairy food-grade by-product. The factorial design revealed that the significant factors were temperature, time, and yeast extract. Then the response surface methodology was used for optimization. At the optimal conditions the viable cell number, CLA, EPSs, and inhibition activity were 2.62 ± 0.49 × 108 CFU/mL, 51.46 ± 1.50 μg/mL, 348.24 ± 5.61 mg/mL and 12.46 ± 0.80 mm, respectively. FTIR, GC, TLC, and SDS page analysis revealed the functional groups of pharmabiotics. The FTIR, GC, TLC, and SDS page analysis showed that both CLA isomers (c-9, t-11, and t-10, c-12) produced. The FTIR, GC, TLC, and SDS page analysis indicated that produced EPSs were composed of glucose, mannose, galactose, xylose, and fructose. FTIR, GC, TLC, and SDS page used to report BACs molecular weight, which showed two fractions by molecular mass 35 and 63 kDa. Previously the ability of different probiotic bacteria investigated and optimized the production of CLA, EPSs, and BACs, but, there was no report on the co-producing capacity of these bioactive metabolites by probiotics. The present work was investigated to optimize the co-production of pharmabiotic metabolites by L. acidophilus LA-5, in supplemented cheese whey as a cultivation medium.

Effects of Lactococcus lactis on the Intestinal Functions in Weaning Piglets

Post-weaning diarrhea of piglets is associated with gut microbiota dysbiosis and intestinal pathogen infection. Recent studies have shown that Lactococcus lactis (L.lactis) could help suppress pathogen infection. This study aimed to investigate the effects of L.lactis on various factors related to growth and immunity in weaning piglets. The results showed that L.lactis improved the growth performance, regulated the amino acid profile (for example, increasing serum tryptophan and ileal mucosal cystine) and the intestinal GABAergic system (including inhibiting ileal gene expression of SLC6A13, GABAAρ1, π, θ, and γ1, and promoting ileal GABAAα5 expression). L.lactis also modulated intestinal immunity by promoting jejunal interleukin 17, 18, 22, ileal toll-like receptor 2, 5, 6, and myeloid differentiation primary response protein 88 gene expression while inhibiting jejunal interferon-γ and ileal interleukin 22 expressions. L.lactis highly affected the intestinal microbiota by improving the beta diversity of gut microbiota and the relative abundance of Halomonas and Shewanella. In conclusion, L.lactis improved the growth performance and regulated amino acid profiles, intestinal immunity and microbiota in weaning piglets.

Adsorption of plantaricin Q7 on montmorillonite and application in feedback regulation of plantaricin Q7 synthesis by Lactobacillus plantarum Q7

Kieselguhr, bentonite, and montmorillonite were investigated as potential carriers of plantaricin Q7. Highest level of adsorption of plantaricin Q7 was obtained with montmorillonite. Meanwhile, visible inhibition zones were observed against Listeria monocytogenes for montmorillonite adsorbed with plantaricin Q7. Adsorption kinetics showed that the adsorption behaviour followed the pseudo-first-order and Weber's intra-particle diffusion models, suggesting two steps had taken place during the adsorption process. X-ray diffraction assays revealed that plantaricin Q7 was intercalated into the interlayer space of montmorillonites. Electrostatic, hydrogen bonding and hydrophobic interactions proved to play important roles in the mechanisms of interaction between montmorillonite and plantaricin Q7, as shown by infrared spectroscopy analysis. In addition, plantaricin Q7 production was inhibited by feedback regulation with its high concentrations. In order to remove product feedback inhibition in plantaricin Q7 production, a strategy was implemented for its adsorption onto montmorillonite during fermentation. The final plantaricin Q7 output reached 3713.40 IU/mL during fermentation using montmorillonite to adsorb plantaricin Q7, 41.61% higher than that of non- montmorillonite. These results indicate that montmorillonites are suitable carriers for plantaricin Q7 adsorption, and the adsorption of plantaricin Q7 onto montmorillonite during fermentation could be a good method to increase final plantaricin Q7 production.

Extraction of Lactobacillus acidophilus CICC 6074 S-Layer Proteins and Their Ability to Inhibit Enteropathogenic Escherichia coli

An adhesion-related protein of Lactobacillus acidophilus strain CICC 6074 involved in binding to Caco-2 cells and inhibiting Enteropathogenic Escherichia coli (EPEC) was isolated and characterized. The S-layer protein was extracted with 5M LiCl and the active fraction purified by gel filtration (G-75). The S-layer protein was visualized by SDS-PAGE and characterized by estimating the relative molecular weight using mass spectra. The inhibitory effect of L. acidophilus and its S-layer proteins on the ability of EPEC to adhere to cells was explored by using a Caco-2 cell model. The results suggest that the S-layer proteins of L. acidophilus are adhesive in nature and are involved in the competitive exclusion of EPEC from Caco-2 cells.

The importance of lactic acid bacteria for the prevention of bacterial growth and their biogenic amines formation: A review

Foodborne pathogens (FBP) represent an important threat to the consumers' health as they are able to cause different foodborne diseases. In order to eliminate the potential risk of those pathogens, lactic acid bacteria (LAB) have received a great attention in the food biotechnology sector since they play an essential function to prevent bacterial growth and reduce the biogenic amines (BAs) formation. The foodborne illnesses (diarrhea, vomiting, and abdominal pain, etc.) caused by those microbial pathogens is due to various reasons, one of them is related to the decarboxylation of available amino acids that lead to BAs production. The formation of BAs by pathogens in foods can cause the deterioration of their nutritional and sensory qualities. BAs formation can also have toxicological impacts and lead to different types of intoxications. The growth of FBP and their BAs production should be monitored and prevented to avoid such problems. LAB is capable of improving food safety by preventing foods spoilage and extending their shelf-life. LAB are utilized by the food industries to produce fermented products with their antibacterial effects as bio-preservative agents to extent their storage period and preserve their nutritive and gustative characteristics. Besides their contribution to the flavor for fermented foods, LAB secretes various antimicrobial substances including organic acids, hydrogen peroxide, and bacteriocins. Consequently, in this paper, the impact of LAB on the growth of FBP and their BAs formation in food has been reviewed extensively.

Fermentation factors influencing the production of bacteriocins by lactic acid bacteria: a review

Lactic acid bacteria (LAB) are the major interest in food industry primarily by virtue of their biopreservative properties.

Biological potency and characterization of antibacterial substances produced by Lactobacillus pentosus isolated from Hentak, a fermented fish product of North-East India

Lactic acid bacteria (LAB) isolated from various foods are important due to their potential to inhibit microorganisms, including drug-resistant bacteria. The objectives of this investigation were to isolate and identify antibacterial substances producing LAB from Hentak, a traditional fermented fish product of Manipur (North-East India), and to optimize the production of antagonistic substances present in cell free neutralized supernatant (CFNS) against enteric bacterial pathogens using the ‘one factor at a time’ (OFAT) method. Out of 10 LAB, the most potent bacterium producing antibacterial substances was isolated and identified as Lactobacillus pentosus strain LAP1 based upon morphological, biochemical and molecular characterization. MRS (de Man, Ragosa and Sharpe) medium was determined to provide better bactericidal activity (AU/ml) than other tested media against the indicator enteric bacteria, including Staphylococcus epidermidis MTTC 3615, Micrococcus luteus MTCC 106, Shigella flexneri MTCC 1457, Yersinia enterocolitica MTCC 840 and Proteus vulgaris MTCC 1771. The culture conditions (pH: 5, temperature: 30 °C and inoculum volume: 1 %) and medium components (carbon source: lactose and nitrogen source: ammonium chloride) were observed to be the most influential parameters of significant antagonistic activity of CFNS against the enteric pathogens. MRS medium supplemented with Tween20 effectively stimulated the yield of antibacterial substances. The CFNS of strain LAP1 exhibited sensitivity to proteolytic enzyme (pepsin) treatment and heat treatment (60 °C for 60 min, 100 °C for 30 min and 121 °C for 15 min) and lost its inhibitory properties. The CFNS was active at an acidic (pH 3.0) to neutral pH (pH 7.0) but lost its antagonistic properties at an alkaline pH. The CFNS obtained from strain LAP1 scavenges the DPPH (1,1-diphenyl-2 picrylhydrazyl) significantly in a concentration-dependent manner within the range of 8.8 ± 0.12–57.35 ± 0.1 %. The OFAT-based approach revealed the baseline for statistical optimization, the scale-up process and efficient production of CFNS by L. pentosus strain LAP1, which could be used as a potential antibacterial and free radical scavenging agent.