In vitro evaluation of resistance to environmental stress by planktonic and biofilm form of lactic acid bacteria isolated from traditionally made cheese from Serbia

Sucrose contributed to the biofilm formation of Tetragenococcus halophilus and changed the biofilm structure

Based on the previous research results that the addition of sucrose in the medium improved the biofilm formation of Tetragenococcus halophilus, the influence of sucrose on biofilm formation was explored. Moreover, the influence of exogenous expression of related genes sacA and galE from T. halophilus on the biofilm formation of L. lactis NZ9000 was investigated. The results showed that the addition of sucrose in the medium improved the biofilm formation, the resistance of biofilm cells to freeze-drying stress, and the contents of exopolysaccharides (EPS) and eDNA in the T. halophilus biofilms. Meanwhile, the addition of sucrose in the medium changed the monosaccharide composition of EPS and increased the proportion of glucose and galactose in the monosaccharide composition. Under 2.5% (m/v) salt stress condition, the expression of gene sacA promoted the biofilm formation and the EPS production of L. lactis NZ9000 with the sucrose addition in the medium and changed the EPS monosaccharide composition. The expression of gene galE up-regulated the proportion of rhamnose, galactose, and arabinose in the monosaccharide composition of EPS, and down-regulated the proportion of glucose and mannose. This study will provide a theoretical basis for regulating the biofilm formation of T. halophilus, and provide a reference for the subsequent research on lactic acid bacteria biofilms.

Microbial biofilms: a comprehensive review of their properties, beneficial roles and applications

Biofilms are microbial communities nested in self-secreted extracellular polymeric substances that can provide microorganisms with strong tolerance and a favorable living environment. Deepening the understanding and research on positive effects of microbial biofilms is consequently necessary, since most researches focuses on how to control biofilms formation to reduce food safety issues. This paper highlights beneficial roles of biofilms including the formation mechanism, influencing factors, health benefits, strategies to improve its film-forming efficiency, as well as applications especially in fields of food industry, agriculture and husbandry, and environmental management. Beneficial biofilms can be affected by multiple factors such as strain characteristics, media composition, signal molecules, and carrier materials. The biofilm barrier composed of beneficial bacteria provides a more favorable microecological environment, keeping bacteria survival longer, and its derived metabolites are better conducive to health. However, in the practical application of biofilms, there are still significant challenges, especially in terms of film-forming efficiency, stability, and safety assessment. Continuous research is needed to discover innovative methods of utilizing biofilms for sustainable food development in the future, in order to fully unleash its potential and promote its application in the food industry.

Beyond Harmful: Exploring Biofilm Formation by Enterococci Isolated from Portuguese Traditional Cheeses

This study investigated the biofilm-forming capabilities of Enterococcus isolates from Portuguese traditional cheeses with protected designation of origin (PDO) status, specifically Azeitão and Nisa. Given the absence of added starter cultures in the cheesemaking process, the characteristics of these cheeses are intrinsically linked to the autochthonous microbiota present in the raw materials and the production environment. Our findings demonstrate that all isolates possess biofilm production abilities, which are crucial for their colonization and persistence within cheese factories, thereby maintaining factory-specific microbial heritage. Through an integrated analysis utilizing principal component analysis (PCA), a direct correlation between biofilm formation and cell viability was established. Notably, these results underscore the adaptive capacity of enterococci to survive environmental fluctuations and their role in the unique characteristics of Portuguese traditional cheeses. Overall, this research enhances our understanding of the microbial dynamics in cheese production and highlights the importance of enterococci in preserving cheese quality and heritage.

Unveiling the Potential of Lactic Acid Bacteria from Serbian Goat Cheese

This study aimed to unleash the potential of indigenous lactic acid bacteria (LAB) originating from traditionally made Serbian goat cheese. Following the isolation and identification of the LAB, the safety aspects of the isolates were evaluated through tests for hemolytic activity and antibiotic sensitivity. The selected isolates were then tested for various technological properties, including growth in methylene blue, proteolytic activity, acidification, curd formation ability in both pure and enriched goat milk, diacetyl production, antagonistic potential against other LAB, and biofilm formation ability. The results indicated that Lactococcus spp., Lacticaseibacillus spp., and Lactiplantibacillus spp. did not exhibit α or β hemolysis, while enterococci displayed α hemolysis. A higher number of isolates demonstrated sensitivity to ampicillin, tetracycline, and streptomycin, while sensitivity to gentamicin and vancomycin was strain-dependent. Based on the evaluation of technological properties, Lacticaseibacillus paracasei M-1 and Lactiplantibacillus plantarum C7-7, C7-8, and C14-5 showed promising characteristics. Additionally, Lactococcus lactis subsp. lactis strains C0-14 and C21-8 emerged as promising candidates with notable technological properties. Notably, certain indigenous strains LAB exhibit promising technological properties and safety profiles. These characteristics make them suitable candidates for use as starter or adjunct cultures in goat's milk cheese production, potentially enhancing the quality and safety of the cheese as well as hygiene practices among small-scale dairy producers.

High-throughput characterization of the effect of sodium chloride and potassium chloride on 31 lactic acid bacteria and their co-cultures

Salt (NaCl) is associated with a risk of hypertension and the development of coronary heart disease, so its consumption should be limited. However, salt plays a key role in the quality and safety of food by controlling undesirable microorganisms. Since studies have focused primarily on the effect of salts on the overall counts of the lactic acid bacteria (LAB) group, we have not yet understood how salt stress individually affects the strains and the interactions between them. In this study, we characterized the effect of sodium chloride (NaCl) and potassium chloride (KCl) on the growth and acidification of 31 LAB strains. In addition, we evaluated the effect of salts on a total of 93 random pairwise strain combinations. Strains and co-cultures were tested at 3% NaCl, 5% NaCl, and 3% KCl on solid medium using an automated approach and image analysis. The results showed that the growth of LAB was significantly reduced by up to 68% at 5% NaCl (p < 0.0001). For the co-cultures, a reduction of up to 57% was observed at 5% NaCl (p < 0.0001). However, acidification was less affected by salt stress, whether for monocultures or co-cultures. Furthermore, KCl had a lesser impact on both growth and acidification compared to NaCl. Indeed, some strains showed a significant increase in growth at 3% KCl, such as Lactococcus lactis subsp. lactis 74310 (23%, p = 0.01). More importantly, co-cultures appeared to be more resilient and had more varied responses to salt stress than the monocultures, as several cases of suppression of the significant effect of salts on acidification and growth were detected. Our results highlight that while salts can modulate microbial interactions, these latter can also attenuate the effect of salts on LAB.

Improving the Viability of Probiotics under Harsh Conditions by the Formation of Biofilm on Electrospun Nanofiber Mat

For improving probiotics’ survivability under harsh conditions, this study used Lactiplantibacillus plantarum GIM1.648 as a model microorganism to investigate its ability to produce biofilms on electrospun ethyl cellulose nanofiber mats. SEM observations confirmed that biofilm was successfully formed on the nanofibers, with the latter being an excellent scaffold material. The optimal cultivation conditions for biofilm formation were MRS medium without Tween 80, a culture time of 36 h, a temperature of 30 °C, a pH of 6.5, and an inoculum concentration of 1% (v/v). The sessile cells in the biofilm exhibited improved gastrointestinal and thermal tolerance compared to the planktonic cells. Additionally, the RT-qPCR assay indicated that the luxS gene played a crucial role in biofilm formation, with its relative expression level being 8.7-fold higher compared to the planktonic cells. In conclusion, biofilm formation on electrospun nanofiber mat has great potential for improving the viability of probiotic cells under harsh conditions.

Engineered Biofilm: Innovative Nextgen Strategy for Quality Enhancement of Fermented Foods

Microbial communities within fermented food (beers, wines, distillates, meats, fishes, cheeses, breads) products remain within biofilm and are embedded in a complex extracellular polymeric matrix that provides favorable growth conditions to the indwelling species. Biofilm acts as the best ecological niche for the residing microbes by providing food ingredients that interact with the fermenting microorganisms' metabolites to boost their growth. This leads to the alterations in the biochemical and nutritional quality of the fermented food ingredients compared to the initial ingredients in terms of antioxidants, peptides, organoleptic and probiotic properties, and antimicrobial activity. Microbes within the biofilm have altered genetic expression that may lead to novel biochemical pathways influencing their chemical and organoleptic properties related to consumer acceptability. Although microbial biofilms have always been linked to pathogenicity owing to its enhanced antimicrobial resistance, biofilm could be favorable for the production of amino acids like l-proline and L-threonine by engineered bacteria. The unique characteristics of many traditional fermented foods are attributed by the biofilm formed by lactic acid bacteria and yeast and often, multispecies biofilm can be successfully used for repeated-batch fermentation. The present review will shed light on current research related to the role of biofilm in the fermentation process with special reference to the recent applications of NGS/WGS/omics for the improved biofilm forming ability of the genetically engineered and biotechnologically modified microorganisms to bring about the amelioration of the quality of fermented food.

Advantages and disadvantages of non-starter lactic acid bacteria from traditional fermented foods: Potential use as starters or probiotics

Traditional fermented foods are a significant source of starter and/or non-starter lactic acid bacteria (nsLAB). Moreover, these microorganisms are also known for their role as probiotics. The potential of nsLAB is huge; however, there are still challenges to be overcome with respect to characterization and application. In the present review, the most important steps that autochthonous lactic acid bacteria isolated from fermented foods need to overcome, to qualify as novel starter cultures, or as probiotics, in food technology and biotechnology, are considered. These different characterization steps include precise identification, detection of health-promoting properties, and safety evaluation. Each of these features is strain specific and needs to be accurately determined. This review highlights the advantages and disadvantages of nsLAB, isolated from traditional fermented foods, discussing safety aspects and sensory impact.

Ribosome Profiling and RNA Sequencing Reveal Genome-Wide Cellular Translation and Transcription Regulation Under Osmotic Stress in Lactobacillus rhamnosus ATCC 53103

To determine whether osmotic pressure affects the translation efficiency of Lactobacillus rhamnosus, the ribosome profiling assay was performed to analyze the changes in translation efficiency in L. rhamnosus ATCC 53103. Under osmotic stress, differentially expressed genes (DEGs) involved in fatty acid biosynthesis and metabolism, ribosome, and purine metabolism pathways were co-regulated with consistent expression direction at translation and transcription levels. DEGs involved in the biosynthesis of phenylalanine, tyrosine, and tryptophan, and the phosphotransferase system pathways also were co-regulated at translation and transcription levels, while they showed opposite expression direction at two levels. Moreover, DEGs involved in the two-component system, amino acid metabolism, and pyruvate metabolism pathways were only regulated at the transcription level. And DEGs involved in fructose and mannose metabolism were only regulated at the translation level. The translation efficiency of DEGs involved in the biosynthesis of amino acids was downregulated while in quorum sensing and PTS pathways was upregulated. In addition, the ribosome footprints accumulated in open reading frame regions resulted in impaired translation initiation and elongation under osmotic stress. In summary, L. rhamnosus ATCC 53103 could respond to osmotic stress by translation regulation and control the balance between survival and growth of cells by transcription and translation.

Joint protection strategies for Saccharomyces boulardii: exogenous encapsulation and endogenous biofilm structure

Biofilms are heterogeneous structures composed of microorganisms and the surrounding extracellular polymeric substances (EPS) that protect the microbial cells from harsh environments. Saccharomyces boulardii is the first yeast classified as a probiotic strain with unique properties. However, tolerance of S. boulardii biofilms to harsh environments especially during production and in the gastrointestine remains unknown. In this study, S. boulardii cells were encapsulated in alginate microcapsules and subsequently cultured to form biofilms, and their survival and tolerance were evaluated. Microencapsulation provided S. boulardii a confined space that enhanced biofilm formation. The thick alginate shell and the mature biofilm improved the ability of S. boulardii to survive under harsh conditions. The exogenous encapsulation and the endogenous biofilm structure together enhanced the gastrointestinal tolerance and thermotolerance of S. boulardii. Besides, as the alginate shell became thinner with an increase in the subsequent culture duration, the EPS of S. boulardii biofilms exerted an important protective effect in resisting high temperatures. The encapsulated biofilm of S. boulardii after 24-h culture exhibited 60 × higher thermotolerance at 60 °C (10 min), while those after 6-h and 24-h culture showed 1000 × to 550,000 × higher thermotolerance at 120 °C (1 min) compared with the planktonic cells without encapsulation. The present study's findings suggest that a combination of encapsulation and biofilm mode efficiently enhanced gastrointestinal tolerance and thermotolerance of S. boulardii. KEY POINTS: • Encapsulated S. boulardii in biofilm mode showed enhanced tolerance. • Exogenous shell and endogenous biofilm provided dual protection to S. boulardii.

Potential Probiotic Pediococcus pentosaceus M41 Modulates Its Proteome Differentially for Tolerances Against Heat, Cold, Acid, and Bile Stresses

Probiotics containing functional food confer health benefits in addition to their nutritional properties. In this study, we have evaluated the differential proteomic responses of a potential novel probiotic Pediococcus pentosaceus M41 under heat, cold, acid, and bile stress conditions. We identified stress response proteins that could provide tolerances against these stresses and could be used as probiotic markers for evaluating stress tolerance. Pediococcus pentosaceus M41 was exposed for 2 h to each condition: 50°C (heat stress), 4°C (cold stress), pH 3.0 (acid stress) and 0.05% bile (bile stress). Proteomic analysis was carried out using 2D-IEF SDS PAGE and LC-MS/MS. Out of 60 identified proteins, 14 upregulated and 6 downregulated proteins were common among all the stress conditions. These proteins were involved in different biological functions such as translation-related proteins, carbohydrate metabolism (phosphoenolpyruvate phosphotransferase), histidine biosynthesis (imidazole glycerol phosphate synthase) and cell wall synthesis (tyrosine-protein kinase CapB). Proteins such as polysaccharide deacetylase, lactate oxidase, transcription repressor NrdR, dihydroxyacetone kinase were upregulated under three out of the four stress conditions. The differential expression of these proteins might be responsible for tolerance and protection of P. pentosaceus M41 against different stress conditions.

Combined proteomics and transcriptomics analysis of Lactococcus lactis under different culture conditions

During industrial handling, Lactococcus lactis needs to adapt to different culture conditions by regulating its metabolic pathways. Modifying culture conditions may be an important way to control the biomass and functional metabolites of lactic acid bacteria. In this study, we identified the differentially expressed genes and proteins of L. lactis under different culture conditions by integrating transcriptomics and proteomics. We also analyzed the data using a bioinformatic approach to reveal the regulatory mechanisms affected by culture conditions. The transcriptome and proteome studies indicated that different culture conditions (fructose, calcium ion, palmitic acid, low pH) affected gene and protein expressions. The levels of differentially expressed proteins did not significantly correlate with the expression levels of their corresponding genes. Our results highlight the importance of comparative transcriptomics and proteomics analyses. In this study, fructose and pH significantly affected sugar metabolism of L. lactis. When lactose was replaced by fructose, fructokinase expression was promoted, and fructose metabolism was accelerated, whereas starch and sucrose metabolism and galactose metabolism system were inhibited. Low pH may be beneficial to homofermentation of L. lactis, which may also metabolize galactose through the tagatose pathway and the Leloir pathway. Fatty acid metabolism and fatty acid biosynthesis were significantly downregulated under calcium ion and palmitic acid. The purine metabolism was upregulated under fructose treatment and downregulated under palmitic acid treatment.

Gentamicin decorated phosphatidylcholine-chitosan nanoparticles against biofilms and intracellular bacteria

Biofilms and intracellular bacteria often cause a series of overwhelming public health issues due to their strong drug resistance. Hence, chitosan nanoparticles (CS NPs), phosphatidylcholine and gentamicin were used to synthesize a novel nanodrug delivery system (GPC NPs). Dynamic light scattering (DLS) demonstrated that the surface zeta-potential of GPC NPs was -19.5 mV. The morphology of GPC NPs was observed by scanning electron microscopy (SEM). The gentamicin adsorption and release behaviors of GPC NPs were also investigated. The GPC NPs could effectively damage and remove the biofilm formed by pathogens through permeation of the antibiotic into the biofilm. In addition, the nanoparticles were readily engulfed by macrophages which facilitated the killing of intracellular bacteria and had neglectable cytotoxicity. Our study indicated that GPC NPs could be used as a promising nanoantibacterial agent against biofilms and intracellular bacteria.

Updates on understanding of probiotic lactic acid bacteria responses to environmental stresses and highlights on proteomic analyses

Probiotics are defined as live microorganisms that improve the health of the host when administered in adequate quantities. Nonetheless, probiotics encounter extreme environmental conditions during food processing or along the gastrointestinal tract. This review discusses different environmental stresses that affect probiotics during food preparation, storage, and along the alimentary canal, including high temperature, low temperature, low and alkaline pH, oxidative stress, high hydrostatic pressure, osmotic pressure, and starvation. The understanding of how probiotics deal with environmental stress and thrive provides useful information to guide the selection of the strains with enhanced performance in specific situations, in food processing or during gastrointestinal transit. In most cases, multiple biological functions are affected upon exposure of the cell to environmental stress. Sensing of sublethal environmental stress can allow for adaptation processes to occur, which can include alterations in the expression of specific proteins.

Autochthonous lactic acid bacteria-presentation of potential probiotics application

OBJECTIVE

The objective of this study was to evaluate the probiotic potential as well as the ability of adhesion and aggregation of natural and autochthonous lactic acid bacteria, isolated from traditionally made cheese.

RESULTS

Lactic acid bacteria from natural food sources can be promising probiotic candidates and they can be used in natural food preservation or like starter cultures. Tested autochthonous isolates showed tolerance to the simulated gastrointestinal condition as well as the sensitivity to clinically relevant antibiotics, especially to ampicillin (MIC at 0.195 μg mL^-1 for lactobacilli and from 0.195 to 3.125 μg mL^-1 for lactococci). Among isolates, the highest percentage of adhesion was detected with chloroform, while the adhesion ability of selected isolates to pig intestinal epithelium was in the correlation with the results of adhesion ability with solvents. The auto-aggregation ability of isolates was demonstrated, while co-aggregation with Escherichia coli was strain specific.

CONCLUSION

The results indicated the potential probiotic properties of the isolates and give evidence for further investigation and potential application in the dairy industry.

Probiotics in Food Systems: Significance and Emerging Strategies Towards Improved Viability and Delivery of Enhanced Beneficial Value

Preserving the efficacy of probiotic bacteria exhibits paramount challenges that need to be addressed during the development of functional food products. Several factors have been claimed to be responsible for reducing the viability of probiotics including matrix acidity, level of oxygen in products, presence of other lactic acid bacteria, and sensitivity to metabolites produced by other competing bacteria. Several approaches are undertaken to improve and sustain microbial cell viability, like strain selection, immobilization technologies, synbiotics development etc. Among them, cell immobilization in various carriers, including composite carrier matrix systems has recently attracted interest targeting to protect probiotics from different types of environmental stress (e.g., pH and heat treatments). Likewise, to successfully deliver the probiotics in the large intestine, cells must survive food processing and storage, and withstand the stress conditions encountered in the upper gastrointestinal tract. Hence, the appropriate selection of probiotics and their effective delivery remains a technological challenge with special focus on sustaining the viability of the probiotic culture in the formulated product. Development of synbiotic combinations exhibits another approach of functional food to stimulate the growth of probiotics. The aim of the current review is to summarize the strategies and the novel techniques adopted to enhance the viability of probiotics.

Probiotics Biofilm-Integrated Electrospun Nanofiber Membranes: A New Starter Culture for Fermented Milk Production

Electrospun nanofiber membranes are widely investigated in the past few decades as candidates for tissue engineering, which can mimic natural extracellular matrix (ECM) and improve cell adhesion, proliferation, and expression on nanofiber membranes. However, the formation of bacterial biofilms on nanofiber membranes and application of the biofilm-integrated nanofiber membranes remain largely unknown. Here, electrospun cellulose acetate nanofiber membranes are first utilized as scaffold materials for Lactobacillus plantarum ( L. plantarum) biofilm formation. Nanofiber membranes proved to be an excellent scaffold for bacteria biofilm with high stability, where biofilms were interlocked with nanofibers forming a cohesive structure. In comparison with planktonic bacteria, L. plantarum biofilms on nanofiber membranes show excellent gastrointestinal resistance. Instead of decreasing, the number of viable cells increased after 3 h digestion in vitro. The L. plantarum biofilm-integrated nanofiber membranes were used as reusable starter cultures for fermented milk production showing excellent fermentative ability and higher survival of L. plantarum during shelf life. The viable cells in fermented milk remained at 11 log CFU/g throughout the reusable batches, which is far above the required value of 7 log CFU/g in commercial products. In addition, the produced fermented milk possesses shorter fermentation time and higher survival of probiotics during shelf life. The results suggest electrospun nanofiber membranes are ideal scaffold materials for bacteria biofilms immobilization in biotechnology and fermentation engineering, which broaden the potential use of electrospun nanofiber membranes in microbiology and strengthen the application of biofilms in fermentation engineering.