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

Revisiting the characteristics of nanomaterials, composites, hybrid and functionalized materials in medical microbiology

Unlike traditional materials designed to form large structures, many modern materials are presented in the form of powders resulting from a molecular level control of their composition and structure, making possible the miniaturization and fine-tuning of their properties to act in cellular dimensions with customized tasks. Several new materials for biomedical and microbiology applications appear every year. Although many of them are called nanomaterials, there may be a more precise description or classification. In this work, we review and detail the structural classification of nanometric, functionalized, hybrid and composite materials, mainly based on descriptions given by the International Union of Pure and Applied Chemistry (IUPAC). Besides we included smart and multifunctional materials, cassification based on performance. The second section shows how these materials are used in the area of medical microbiology, grouping these applications into barriers for microorganisms on surfaces, disinfectants in clinical practice, targeting of pathogens, detectors of microorganisms or their metabolites, and also as substrates to stabilize, transport, or nourish beneficial microorganisms. Finally, we will discuss some evidence that indicates the environmental risk and bacterial resistance alerts that should be taken into account with the use of these advanced powder materials.

Shaping the Future of Functional Foods: Using 3D Printing for the Encapsulation and Development of New Probiotic Foods

Consumers have been demanding foods that, besides providing nutrition, bring some health benefits, known as functional foods. The insertion of probiotics in foods is a strategy for developing functional foods. Still, it has been a challenge because these matrices have different pHs and undergo different process temperatures and times that can reduce the viability of these microorganisms. In this sense, encapsulation using 3D printing emerges to protect probiotic microorganisms and ensure that they reach the intestine viable and carry out the expected beneficial action. Thus, this review evaluates the current advancements in 3D printing to encapsulate and develop novel probiotic foods. Research has shown that 3D printing effectively encapsulates probiotic microorganisms, preserving their viability throughout the gastrointestinal tract. Studies have proven the effectiveness of 3D printing encapsulation in protecting probiotics during processing, storage, and digestion. Innovative formulations for 3D bioprinted products with probiotics, such as food structures based on cereals, mashed potatoes, and cream, have been developed. Producing products with shelf life and combining applications of phytochemicals and probiotics aims to improve personalized nutrition, textural characteristics, and sensory attributes of the foods produced by this emerging approach. Therefore, 3D printing of foods with probiotics has the potential to create new products that meet this demand.

Cross-over fermentation dynamics and proteomic properties of acid gels with indigenous Lactobacillus spp. isolated from cheeses

The present study examined the proteomic characteristics and fermentation dynamics of indigenous bacteria isolated from traditional Mihalic cheese in an acid gel matrix. Accordingly, autochthonous strains of Levilactobacillus brevis, Lacticaseibacillus paracasei, and Lacticaseibacillus rhamnosus were adapted to the gel matrix alongside commercial yogurt culture (Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus). The study evaluated bacterial activity, proteolytic behavior, physicochemical characteristics, and textural and sensory properties in acid gel samples. The microorganisms demonstrated high survival rates (>7.35 log₁₀ cfu/g) in the fermented gel system and induced limited acidification throughout the product's shelf life. Regarding proteomic properties, the highest amino acid variation during the shelf life was observed in the FMB sample (28.20%). Furthermore, arginine, leucine, phenylalanine, aspartic acid, lysine, and cysteine reductions were noted in samples containing the isolated microorganisms. Including indigenous microorganisms in the fermented milk increased the levels of essential amino acids. Principal Component Analysis of sensory properties revealed that samples containing indigenous microorganisms differed significantly from the control sample (C), which contained only commercial yogurt culture. The results revealed the proteolytic changes associated with fermentation, including producing free amino acids as nutritional components, forming specific aroma compounds, and modifying textural and sensory properties. These results demonstrate the potential of utilizing local cultures to develop products enriched with novel bioactive components, offering consumers enhanced nutritional and sensory benefits.

Effects of luxS gene on biofilm formation and fermentation property in Lactobacillus plantarum R

The biofilm formation of Lactobacilli is regulated by the LuxS/AI-2 quorum sensing (QS) system, but the mechanism of QS regulating the formation of Lactobacilli biofilm is not clear. This study aimed to investigate the mechanism of producing biofilm in L. plantarum R and its effect on the quality of fermented pickles based on LuxS/AI-2 QS system. Compared with L. plantarum R, the AI-2 activity of L. plantarum RΔluxS was significantly reduced, but the biofilm, extracellular protein, and eDNA were significantly increased. Moreover, expression of oppA, livJ, livH and comD genes was up-regulated and luxS, peg.3090 and peg.3093 was down-regulated. Results showed that peg.3093 was most significantly down-regulated in L. plantarum RΔluxS, and extremely significant negatively correlated with biofilm. The biofilm, eDNA, and extracellular protein of L. plantarum RΔpeg.3093 was higher than those of L. plantarum R. Moreover, metabolomics showed that deletion of luxS gene could decrease AI-2 level, promote anthocyanin and flavonol biosynthesis, lead to improving the antioxidant properties and quality of pickles. Thus, luxS gene knockout may increase biofilm by down-regulating the expression of peg.3093 to increase extracellular protein and eDNA. This study provides a theoretical basis for the enhancement of Lactobacillus biofilm and its application.

Regulatory mechanisms and applications of Lactobacillus biofilms in the food industry

Lactobacillus is widely recognized for its probiotic benefits and has been widely used in food production. While biofilms are typically associated with pathogenic bacteria, they also served as a self-protective mechanism formed by microorganisms in an adverse environments. In recent years, relevant studies have revealed the excellent characteristics of Lactobacillus biofilms, offering new insights into their potential applications in the food industry. The Lactobacillus biofilms is important in improving fermentation processes and enhancing the resilience of Lactobacillus in various conditions. This paper reviews how quorum sensing regulates the formation of Lactobacillus biofilms and explores their roles in stress resistance, bacteriostasis and food production. Additionally, it highlights the emerging concept of fourth-generation probiotics, developed through biofilm technology, as a novel approach to probiotic applications.

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.

Fabric Fiber as a Biofilm Carrier for Halomonas sp. H09 Mixed with Lactobacillus rhamnosus GG

Biofilm bacteria have stronger resistance to the adverse external environment compared to planktonic bacteria, and biofilms of non-pathogenic bacteria have strong potential for applications in food. In this experiment, Halomonas sp. H09 and Lactobacillus rhamnosus GG, which have film-forming ability in monoculture and better film-forming ability in mixed culture than the two strains alone, were selected as the target strains for mixed culture. According to SEM observation and bacterial dry weight measurement, the target strain formed a dense biofilm on a 0.1 g/L chitosan-modified cellulose III carrier. Furthermore, the presence of extracellular polymeric substances in biofilms was verified by EDS and FTIR. The results showed that 0.1 g/L chitosan-modified cellulose III was an ideal carrier material for immobilization of Halomonas sp. H09 with Lactobacillus rhamnosus GG biofilm. This research provided a basis for the selection of non-pathogenic mixed-bacteria biofilm carriers.

Lactobacillus reuteri biofilms formed on porous zein/cellulose scaffolds: Synbiotics to regulate intestinal microbiota

Supplementing probiotics or indigestible carbohydrates is a usual strategy to prevent or revert unhealthy states of the gut by reshaping gut microbiota. One criterion that probiotics are efficacious is the capacity to survive in the gastrointestinal tract. Biofilm is the common growth mode of microorganisms with high tolerances toward harsh environments. Suitable scaffolds are crucial for successful biofilm culture and large-scale production of biofilm-phenotype probiotics. However, the role of scaffolds containing indigestible carbohydrates in biofilm formation has not been studied. In this study, porous zein/cellulose composite scaffolds provided nitrogen sources and carbon sources simultaneously at the solid/liquid interfaces, being beneficial to the biofilm formation of Lactobacillus reuteri. The biofilms showed 2.1-17.4 times higher tolerances in different gastrointestinal conditions. In human fecal fermentation, the biofilms combined with the zein/cellulose composite scaffolds act as the "synbiotics" positively modulating the gut microbiota and the short-chain fatty acids (SCFAs), where biofilms provide probiotics and scaffolds provide prebiotics. The "synbiotics" show a more positive regulation ability than planktonic L. reuteri, presenting potential applications in gut health interventions. These results provide an understanding of the synergistic effects of biofilm-phenotype probiotics and indigestible carbohydrates contained in the "synbiotics" in gut microbiota modulation.

The interaction among Kluyveromyces marxianus G-Y4, Lacticaseibacillus paracasei GL1, and Lactobacillus helveticus SNA12 and signaling molecule AI-2 participate in the formation of biofilm

In this study, two strains of lactic acid bacteria (Lacticaseibacillus paracasei GL1 and Lactobacillus helveticus SNA12) and one yeast strain of Kluyveromyces marxianus G-Y4 (G-Y4) isolated from Tibetan kefir grains were co-cultured. It was found that the addition of G-Y4 could not only promote the growth of lactic acid bacteria, but also increase the release of metabolites (lactic acid, ethanol, and amino nitrogen). Furthermore, the addition of live cells and cell-free fermentation supernatant (CFS) of G-Y4 could increase the ability of biofilm formation. Morever, the surface characteristics results showed that the addition of G-Y4 live cells could enhance the aggregation ability and hydrophobicity of LAB. Meanwhile, adding live cells and CFS of G-Y4 could promote the release of signaling molecule AI-2 and enhance the expression of the LuxS gene related to biofilm formation. In addition, Fourier-transform infrared spectroscopy and chemical composition analysis were used to investigate the composition of the biofilm, and the results indicated that the biofilm was mainly composed of a small amount of protein but it was rich in polysaccharides including glucose, galactose, and mannose with different ratios. Finally, the formation of biofilm could delay the decline of the number of viable bacteria in storage fermented milk.

Probiotic Lactobacillus paragasseri K7 Nanofiber Encapsulation Using Nozzle-Free Electrospinning

Probiotics are live microorganisms that can have beneficial effects on humans. Encapsulation offers them a better chance of survival. Therefore, nozzle-free electrospinning was introduced for their embedding in nanofibrous material. Probiotic Lactobacillus paragasseri K7 in lyophilized and fresh form, with and without inulin as prebiotic, was added to a polymer solution of sodium alginate (NaAlg) and polyethylene oxide (PEO). Conductivity, viscosity, pH, and surface tension were determined to define the optimal concentration and volume ratio for smooth electrospinning. The success of the formed nanoscale materials was examined by scanning electron microscope (SEM), while the entrapment of probiotics in the nanofibrous mats was detected by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). Spontaneous diffusion of bacteria from electrospun samples in PBS buffer pH 7.4 was studied by plate counting on MRS agar. By exposing polymer solutions containing L. paragasseri K7 and inulin to a high electric field, the nanofilm was formed on a polypropylene substrate, used as collecting material. When polymer solutions without inulin were used, the bead-like nanofibers may have become visible. The SEM results suggest that inulin, in addition to K7 strain, additionally lowers the conductivity of spinning macromolecular solution and hinders the nanofiber formation. The results of ATR-FTIR confirmed the presence of L. paragasseri K7 embedded in nanocomposites by the appearance of characteristic peaks. The samples containing the probiotic regardless of its form with inulin had similar surface composition, except that the sodium content was higher in the samples with fresh probiotic, probably due to greater and thus less easy embedding of the bacteria in NaAlg. Within 2 h, the largest amount of probiotic strain K7 was spontaneously released from the electrospun sample containing the inulin and probiotic in freeze-dried form (44%), while the amount released from the nanofibrous sample, which also contained the inulin and probiotic in fresh form, was significantly lower (21%). These preliminary results demonstrate the potential of nozzle-free electrospinning technology for the development of probiotic delivery systems for short-term use, such as feminine hygiene materials (tampons, pads, napkins).

Endophytic fungus from Handroanthus impetiginosus immobilized on electrospun nanofibrous membrane for bioremoval of bisphenol A

The current industrial and human activities scenario has accelerated the widespread use of endocrine-disrupting compounds (EDCs), which can be found in everyday products, including plastic containers, bottles, toys, cosmetics, etc., but can pose a severe risk to human health and the environment. In this regard, fungal bioremediation appears as a green and cost-effective approach to removing pollutants from water resources. Besides, immobilizing fungal cells onto nanofibrous membranes appears as an innovative strategy to improve remediation performance by allowing the adsorption and degradation to occur simultaneously. Herein, we developed a novel nanostructured bioremediation platform based on polyacrylonitrile nanofibrous membrane (PAN NFM) as supporting material for immobilizing an endophytic fungus to remove bisphenol A (BPA), a typical EDC. The endophytic strain was isolated from Handroanthus impetiginosus leaves and identified as Phanerochaete sp. H2 by molecular methods. The successful assembly of fungus onto the PAN NFM surface was confirmed by scanning electron microscopy (SEM). Compared with free fungus cells, the PAN@H2 NFM displayed a high BPA removal efficiency (above 85%) at an initial concentration of 5 ppm, suggesting synergistic removal by simultaneous adsorption and biotransformation. Moreover, the biotransformation pathway was investigated, and the chemical structures of fungal metabolites of BPA were identified by ultra-high performance liquid chromatography - high-resolution mass (UHPLC-HRMS) analysis. In general, our results suggest that by combining the advantages of enzymatic activity and nanofibrous structure, the novel platform has the potential to be applied in the bioremediation of varied EDCs or even other pollutants found in water resources.

Biomaterials and Encapsulation Techniques for Probiotics: Current Status and Future Prospects in Biomedical Applications

Probiotics have garnered significant attention in recent years due to their potential advantages in diverse biomedical applications, such as acting as antimicrobial agents, aiding in tissue repair, and treating diseases. These live bacteria must exist in appropriate quantities and precise locations to exert beneficial effects. However, their viability and activity can be significantly impacted by the surrounding tissue, posing a challenge to maintain their stability in the target location for an extended duration. To counter this, researchers have formulated various strategies that enhance the activity and stability of probiotics by encapsulating them within biomaterials. This approach enables site-specific release, overcoming technical impediments encountered during the processing and application of probiotics. A range of materials can be utilized for encapsulating probiotics, and several methods can be employed for this encapsulation process. This article reviews the recent advancements in probiotics encapsulated within biomaterials, examining the materials, methods, and effects of encapsulation. It also provides an overview of the hurdles faced by currently available biomaterial-based probiotic capsules and suggests potential future research directions in this field. Despite the progress achieved to date, numerous challenges persist, such as the necessity for developing efficient, reproducible encapsulation methods that maintain the viability and activity of probiotics. Furthermore, there is a need to design more robust and targeted delivery vehicles.

Preparation of milk-based probiotic lactic acid bacteria biofilms: A new generation of probiotics

Biofilm is considered as a community of microorganisms in which cells adhere to each other on surfaces in a self-produced matrix of extracellular polymer compounds. In recent years, efforts to use the beneficial aspects of biofilm in probiotic research have intensified. In this study, probiotic biofilms of Lactiplantibacillus plantarum and Lacticaseibacillus rhamnosus were manufactured using milk and transferred to yogurt in whole and pulverized forms to test in real food conditions. Survival was assessed during 21 days of storage time as well as gastrointestinal conditions. The results indicated that Lp. plantarum and Lc. rhamnosus can form a very desirable and strong biofilm that can have a good protective effect on the survival of these bacteria in probiotic yogurt during processing, storage, and gastrointestinal conditions, in a way that, after 120 min of treatment in high acidic gastrointestinal conditions (pH 2.0), the survival rate decreased by only 0.5 and 1.1 log CFU/ml. Probiotic biofilm can be used as a natural way of utilizing bacteria in biotechnology and fermentation, which is an excellent way to increase the utility of probiotics.

Electrospinning and Electrospraying: Emerging Techniques for Probiotic Stabilization and Application

Probiotics are beneficial for human health. However, they are vulnerable to adverse effects during processing, storage, and passage through the gastrointestinal tract, thus reducing their viability. The exploration of strategies for probiotic stabilization is essential for application and function. Electrospinning and electrospraying, two electrohydrodynamic techniques with simple, mild, and versatile characteristics, have recently attracted increased interest for encapsulating and immobilizing probiotics to improve their survivability under harsh conditions and promoting high-viability delivery in the gastrointestinal tract. This review begins with a more detailed classification of electrospinning and electrospraying, especially dry electrospraying and wet electrospraying. The feasibility of electrospinning and electrospraying in the construction of probiotic carriers, as well as the efficacy of various formulations on the stabilization and colonic delivery of probiotics, are then discussed. Meanwhile, the current application of electrospun and electrosprayed probiotic formulations is introduced. Finally, the existing limitations and future opportunities for electrohydrodynamic techniques in probiotic stabilization are proposed and analyzed. This work comprehensively explains how electrospinning and electrospraying are used to stabilize probiotics, which may aid in their development in probiotic therapy and nutrition.

Phenotypic Traits and Probiotic Functions of Lactiplantibacillus plantarum Y42 in Planktonic and Biofilm Forms

Bacteria in planktonic and biofilm forms exhibit different phenotypic properties. In this study, the phenotypic traits and probiotic functions of Lactiplantibacillus plantarum Y42 in planktonic and biofilm forms were assessed. After 36 h of static culture, scanning electron microscopy and confocal laser scanning microscopy showed that the L. plantarum Y42 bacterial cells contained interconnected adhesive matter on the surface, forming a ~18 μm layer of dense biofilms. The surface properties of L. plantarum Y42 in biofilm form, including autoaggregation ability, hydrophobicity, acid-base charge, and adhesiveness, were all higher than those in the planktonic form. Biofilm L. plantarum Y42 showed a higher tolerance to adverse environmental conditions and a higher survival rate, enzymatic activity, and integrity after vacuum lyophilization. And biofilm L. plantarum Y42 had higher adhesion to human enterocyte HT-29 cell monolayers, inhibited the expressions of proinflammatory factors IL-6 and TNF-α, and promoted the expressions of the anti-inflammatory factor IL-10 and barrier proteins Claudin-1 and Occludin. In addition, L. plantarum Y42 in biofilm form can inhibit the adhesion and invasion of Listeria monocytogenes ATCC 19115 to HT-29 cell monolayers and is more effective in relieving the inflammatory reactions and injuries of HT-29 cells caused by L. monocytogenes ATCC 19115. In conclusion, L. plantarum Y42 in biofilm form exhibited better probiotic functions compared to that in planktonic form. This indicated that L. plantarum Y42 can form biofilms to enhance its probiotic functions, which provided a theoretical basis for better development and utilization of L. plantarum Y42.

Biofilm-based delivery approaches and specific enrichment strategies of probiotics in the human gut

The use of probiotics has been one of the effective strategies to restructure perturbed human gut microbiota following a disease or metabolic disorder. One of the biggest challenges associated with the use of probiotic-based gut modulation strategies is to keep the probiotic cells viable and stable during the gastrointestinal transit. Biofilm-based probiotics delivery approaches have emerged as fascinating modes of probiotic delivery in which probiotics show significantly greater tolerance and biotherapeutic potential, and interestingly probiotic biofilms can be developed on food-grade surfaces too, which is ideal for the growth and proliferation of bacterial cells for incorporation into food matrices. In addition, biofilms can be further encapsulated with food-grade materials or with bacterial self-produced biofilms. This review presents a newly emerging and unprecedently discussed techniques for the safe delivery of probiotics based on biofilms and further discusses newly emerging prebiotic materials which target specific gut microbiota groups for growth and proliferation.

Lactobacillus reuteri Biofilms Inhibit Pathogens and Regulate Microbiota in In Vitro Fecal Fermentation

Bacteria colonizing the gastrointestinal tract generally grow well in biofilms. In recent years, probiotic biofilms have been considered the most promising fourth-generation probiotics. However, the research into the functions of probiotic biofilms is just starting. In this study, Lactobacillus reuteri DSM 17938 biofilms formed on electrospun cellulose acetate nanofibrous scaffolds were contrasted with planktonic cells. Pathogen inhibition analysis of Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes suggested a significant distinction between the planktonic and biofilm groups. In human fecal fermentation, L. reuteri remodeled the microbiota by decreasing the relative abundances of Proteobacteria, Escherichia-Shigella, and Desulfovibrio and increasing the relative abundances of Phascolarctobacterium, Bacteroides, and Lactobacillus. Moreover, L. reuteri biofilms played more positive roles in microbiota modulation and short-chain fatty acid production than planktonic L. reuteri. These findings provide an understanding of the beneficial effects of probiotic biofilms, laying a foundation for the application of probiotic biofilms as a health promoter.

Electrospun Nanofibrous Membranes Accelerate Biofilm Formation and Probiotic Enrichment: Enhanced Tolerances to pH and Antibiotics

Biofilms are the oldest, most successful, and most widely distributed form of microorganism life on earth, existing even in extreme environments. Presently, probiotics in biofilm phenotype are thought as the most advanced fourth-generation probiotics. However, high-efficiency and large-scale biofilm enrichment in an artificial way is difficult. Here, fibrous membranes as probiotic biofilm-enriching materials are studied. Electrospun cellulose acetate nanofibrous membranes with nano-sized fibers show outstanding superiority over fibrous membranes with micron-sized fibers in Lactobacillus paracasei biofilm enrichment. The special 3D structure of electrospun nanofibrous membranes makes other facilitating biofilm formation factors insignificant. With a suitable scaffold/culture medium ratio, nearly 100% of L. paracasei cells exist as biofilm phenotype on the membrane from the very beginning, not planktonic state. L. paracasei biofilms possess a potential for long-term survival and high tolerances toward strong acidic and alkali conditions and antibiotics. RNA sequencing results explain why L. paracasei biofilms possess high tolerances toward harsh environments as compared to planktonic L. paracasei. Electrospun nanofibrous membranes can serve as powerful biofilm-enriching scaffolds for probiotics and other valuable microbes.

Lactiplantibacillus plantarum Y42 in Biofilm and Planktonic States Improves Intestinal Barrier Integrity and Modulates Gut Microbiota of Balb/c Mice

In our previous study, Lactiplantibacillus plantarum Y42 showed some potential probiotic functions and the ability to form biofilm. The aim of this study was to compare the similarities and differences in the probiotic and physiological traits of L. plantarum Y42 in the biofilm and planktonic states. L. plantarum Y42 in the biofilm state was proven to have higher survival after passing through mimic gastrointestinal fluid, as well as excellent adhesion properties on the HT-29 cell monolayers, than those in the planktonic state. The expression of tight junction proteins (TJ proteins) of HT-29 cell monolayers treated by L. plantarum Y42 in the planktonic state increased, while similar changes were not observed in the HT-29 cells treated by the strain in the biofilm state. Furthermore, Balb/c mice were orally administered L. plantarum Y42 in the biofilm and planktonic states, respectively. Compared to the planktonic state, the oral administration of L. plantarum Y42 in the biofilm state significantly boosted IgA levels and improved the immunity of the mice. High-throughput sequencing showed that the diversity and structure of the intestinal flora of the mice were changed after the oral administration of L. plantarum Y42, including the up-regulated relative abundance of Lactobacillus in the intestinal tract of the mice, with no difference between the biofilm and planktonic states. Moreover, oral administration of L. plantarum Y42 in biofilm and planktonic states reduced the release of proinflammatory factors, to a certain extent, in the serum of the mice. The similarities and differences in the probiotic and physiological properties of L. plantarum Y42 in the biofilm and planktonic states can be contributed to the reasonable application of the strain.

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.

Biofilm-Integrated Glycosylated Membrane for Biosuccinic Acid Production

Biofilm-based cell-immobilized fermentation technology is regarded as the technique with the most potential for biobased product (chemicals, biofuelss materials, etc.) production in industry. Glycosylated membrane can mimic natural extracellular matrix (ECM) and improve cell adhesion and biofilm formation based on carbohydrate-microbial lectin interaction. Here, we applied glycosylated membrane with rhamnose modified surface for constructing Actinobacillus succinogenes biofilm and producing biosuccinic acid. Polymer hollow fiber (PHF) membrane surface was first modified by glycosylation based on physical adsorption approach. The approach is simple, green, and suitable for scale-amplification. Then, the microbial biofilm formed dramatically on the modified membrane surface. And for subsequent biosuccinic acid production, the maximum titer of succinic acid reached 67.3 g/L, and the yield was 0.82 g/g. Compared with free cell fermentation, the titer and yield increased by 18% and 9% in this biofilm-based cell-immobilized fermentation system, respectively. Importantly, the production efficiency of biosuccinic acid increased obviously for subsequent biofilm-based cell-immobilized fermentation. In addition, the biofilm-integrated glycosylated membrane showed high reusability for succinic acid production. This result is important for developing biofilms for a wide range of applications in bioproduct (chemicals, biofuels, materials, etc.) production.

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.

Milk Fermentation by Lacticaseibacillus rhamnosus GG and Streptococcus thermophilus SY-102: Proteolytic Profile and ACE-Inhibitory Activity

Health benefits of probiotics and production of inhibitors of angiotensin converting enzyme (ACE) released during milk fermentation are well known. That is why in this investigation the proteolytic profile and ACE inhibitory capacity of peptide fractions from protein hydrolysis of milk during fermentation processes was analyzed. Milk fermentation was carried out inoculating 106 CFU of L. rhamnosus GG, S. thermophilus SY-102 and with both bacteria. The proteolytic profile was determined using: TNBS, SDS-PAGE and SEC-HPLC techniques. In vitro ACE inhibition capacity was measured. The pH of 4.5 was reached at 56 h when the milk was fermented with L. rhamnosus, at 12 h with S. thermophillus and at 41 h in the co-culture. Production of free amino groups corresponded with the profile of low molecular weight peptides observed by SDS-PAGE and SEC-HPLC. Co-culture fermentation showed both the highest concentration of low molecular weight peptides and the ACE inhibitory activity (>80%). Results indicated that the combination of lactic cultures could be useful in manufacture of fermented milk with an added value that goes beyond basic nutrition, such as the production of ACE-inhibitory peptides.

Improving the Viability and Metabolism of Intestinal Probiotic Bacteria Using Fibre Obtained from Vegetable By-Products

This study evaluated the effect of dietary fibre obtained from pomegranate, tomato, grape and broccoli by-products on the gastrointestinal transit survival, growth, and metabolism of six probiotic strains. The results showed that the studied by-products contained variable amounts of polysaccharides that affected the six probiotic microorganisms in different ways. In addition, the protective effect of the fibre obtained on the probiotic strains was more effective in the case of the fibre obtained from tomato peel. In terms of growth, grape stems showed the best results, favouring the growth of lactic acid bacteria. Finally, all fibres were able to increase the content of short-chain fatty acids in the in vitro test, but broccoli stems and pomegranate peel stimulated higher production of short-chain fatty acids. The results of this study demonstrate that plant by-product fibres can improve survival, growth, and metabolism in terms of the fatty acid profiles of probiotic strains, highlighting the desirability of harnessing these by-product fibres to develop new high-value-added ingredients as probiotic carriers.

Encapsulation of Lactobacillus in Low-Methoxyl Pectin-Based Microcapsules Stimulates Biofilm Formation: Enhanced Resistances to Heat Shock and Simulated Gastrointestinal Digestion

Encapsulation is a common approach to improve the bacterial survival of probiotics. In this study, two new low-methoxyl pectins (CMP-6 and CMP-8) were used as coating materials to produce microcapsules (MCs) for the encapsulation of Lactobacillus acidophilus LMG9433^T, Lactobacillus casei LMG6904^T, and Lactobacillus rhamnosus LMG25859. A fermentation test showed that encapsulation did not influence the fermentation ability of lactobacilli. The biofilm formation of encapsulated lactobacilli was stimulated when an in situ cultivation was conducted on MCs, which was verified by cryo-SEM observation. The resultant biofilm-forming MCs (BMCs) contained high-density bacterial cells (∼10¹⁰ CFU/mL). Compared to planktonic lactobacilli, pectin-based MCs showed significant protection for encapsulated lactobacilli from heat shock and simulated gastric digestion. Especially, benefiting from the biofilm formation, BMCs provided higher protection with enhanced resistance to heat shock, freeze-drying, and gastrointestinal digestion than MCs. Our result highlighted the superior bacterial resistances of biofilm-forming probiotics encapsulated in pectinate microcapsules.

Applications of bacteria and their derived biomaterials for repair and tissue regeneration

Microorganisms such as bacteria and their derived biopolymers can be used in biomaterials and tissue regeneration. Various methods have been applied to regenerate damaged tissues, but using probiotics and biomaterials derived from bacteria with improved economic-production efficiency and highly applicable properties can be a new solution in tissue regeneration. Bacteria can synthesize numerous types of biopolymers. These biopolymers possess many desirable properties such as biocompatibility and biodegradability, making them good candidates for tissue regeneration. Here, we reviewed different types of bacterial-derived biopolymers and highlight their applications for tissue regeneration.

Effects of okara and vitamin B2 bioenrichment on the functional properties and in vitro digestion of fermented soy milk

Due to highly nutritious and well-known prebiotic nature, okara (soy by-product) can improve the physiological benefits of probiotic consumption by enhancing the physicochemical stability and bioavailability of bacteria and metabolites, partially in food matrices and then in gastrointestinal tract. Initially, vitamin B₂ producing probiotic Lactobacillus plantarum UFG10 was immobilized with 4% okara for soy milk fermentation. SEM micrographs showed firm adherence of UFG10 to okara surface depicting efficient immobilization. Soy milk fermented with okara immobilized UFG10 showed enhanced β-glucosidase activity, stimulating the biotransformation of isoflavones from glucosides (daidzin, from 27.78 to 9.84 μg/mL; genistin, from 32.58 to 8.33 μg/mL) to aglycones (daidzein, from 0.19 to 30.84 μg/mL; genistein, from 1.42 to 33.10 μg/mL) and higher B₂ production (1.53 μg/mL, 12 h) confirmed by HPLC. Okara addition and B₂ enrichment could yield relatively higher antioxidant strength than control soy milk. PLSR correlation revealed the effects of okara and B₂ on the functional properties of soy milk. After okara immobilization, soy milk showed higher soy protein digestibility after in vitro digestion for 225 min, higher aggregation, and lower protein molecular chains, qualitatively confirmed with Atomic force microscope. Okara immobilized bacterial cells exhibited relatively greater resistance up to 55.1% (p < 0.05) in simulated GIT, indicating okara as an ideal substrate for an efficient immobilization which ultimately improved the fate of soy B₂ and protein bioaccessibility and functional products such as isoflavones for micro structural design of soy milk with improved nutrition and digestibility.

Improved digestive stability of probiotics encapsulated within poly(vinyl alcohol)/cellulose acetate hybrid fibers

Novel cellulose acetate (CA) and poly(vinyl alcohol) (PVA) hybrid fibers, fabricated via angled dual-nozzle electrospinning, were used for the encapsulation of probiotics to enhance their gastrointestinal stability. In this study, Escherichia coli strain Nissle 1917 (EcN) cells were encapsulated within PVA/CA composite mats, where CA enhanced the bacterial stability under gastric conditions and PVA provided protection against the toxic solvent during the electrospinning process. Scanning electron microscopy images revealed that EcN was successfully encapsulated within the hybrid fibers. In the simulated digestive system, free cells lost their viability within 100 min, whereas PVA/CA-encapsulated cells survived with a final count of 3.9 log CFU/mL (from an initial count of 7.8 log CFU/mL), an increase of 1 log CFU/mL compared with those in PVA/PVA fibers. Considering the enhanced viability of the encapsulated cells in the gastrointestinal system, multi-nozzle electrospinning is a promising technique for the fabrication of novel matrices for probiotic encapsulation.

Electrospun Scaffold for Biomimic Culture of Caco-2 Cell Monolayer as an In Vitro Intestinal Model

The Caco-2 cell monolayer has been extensively used for the high-throughput assessing of nutrient absorption, screening of drug permeability, and studying the intestinal physiological process in vitro. The most used Caco-2 cell model is the Transwell model with polycarbonate microporous membranes. However, Caco-2 cells in the classical Transwell model need 21 days to gain an intact and mature monolayer. Electrospun nanofiber scaffolds mimicking the natural extracellular matrix could improve cell adhesion, proliferation, and expression, whereas there are no reports that intestinal cells were cultured on the electrospun nanofiber scaffolds. Here, electrospun polylactic acid (PLA) nanofiber scaffolds were chosen as the ideal scaffolds for Caco-2 cell monolayers to construct a modified Transwell. Cell morphology and polarity were studied. Monolayer barrier properties were assessed by measuring transepithelial electrical resistance (TEER) and the leakage of phenol red. As found, intact Caco-2 cell monolayers were formed on the PLA nanofiber scaffolds after 4 days of culture. After 4 days, the TEER increased to 422 Ω·cm² and the apparent permeability coefficients of phenol red decreased to 1.0 ± 0.1 × 10^-6 cm/s, suggesting that Caco-2 cell monolayers developed a formidable barrier to small molecules on the surface of PLA nanofiber scaffolds. Microvilli and tight junctions were clearly visible after day 3. Besides, Caco-2 cell monolayers on the surface of PLA nanofiber scaffolds presented higher differentiation properties than on the surface of the polycarbonate microporous membrane in traditional Transwell including higher alkaline phosphatase activity and higher P-gp activity. Results of quercetin absorption and probiotics adhesion demonstrated that Caco-2 cell monolayers formed on the surface of PLA nanofiber scaffolds also had better physiological function and prediction function in vitro. Overall, the present study indicated that the Transwell with the structurally and functionally biomimetic electrospun PLA nanofiber scaffold could be potentially developed as a promising in vitro intestinal model.

Antibacterial Porous Electrospun Fibers as Skin Scaffolds for Wound Healing Applications

Electrospun fiber scaffolds have a huge potential for the successful treatment of infected wounds based on their unique properties. Although several studies report novel drug-loaded electrospun fiber-based biomaterials, many of these do not provide information on their interactions with eukaryotic and bacterial cells. The main aim of this study was to develop antibacterial drug-loaded porous biocompatible polycaprolactone (PCL) fiber scaffolds mimicking the native extracellular matrix for wound healing purposes. Mechanical property evaluation and different biorelevant tests were conducted in order to understand the structure-activity relationships and reveal how the surface porosity of fibers and the fiber diameter affect the scaffold interactions with the living bacterial and eukaryotic fibroblast cells. Cell migration and proliferation assays and antibiofilm assays enabled us to enlighten the biocompatibility and safety of fiber scaffolds and their suitability to be used as scaffolds for the treatment of infected wounds. Here, we report that porous PCL microfiber scaffolds obtained using electrospinning at high relative humidity served as the best surfaces for fibroblast attachment and growth compared to the nonporous microfiber or nonporous nanofiber PCL scaffolds. Porous chloramphenicol-loaded microfiber scaffolds were more elastic compared to nonporous scaffolds and had the highest antibiofilm activity. The results indicate that in addition to the fiber diameter and fiber scaffold porosity, the single-fiber surface porosity and its effect on drug release, mechanical properties, cell viability, and antibiofilm activity need to be understood when developing antibacterial biocompatible scaffolds for wound healing applications. We show that pores on single fibers within an electrospun scaffold, in addition to nano- and microscale diameter of the fibers, change the living cell-fiber interactions affecting the antibiofilm efficacy and biocompatibility of the scaffolds for the local treatment of wounds.

Electrospun Nanofibers as Carriers of Microorganisms, Stem Cells, Proteins, and Nucleic Acids in Therapeutic and Other Applications

Electrospinning is a technique that uses polymer solutions and strong electric fields to produce nano-sized fibers that have wide-ranging applications. We present here an overview of the use of electrospinning to incorporate biological products into nanofibers, including microorganisms, cells, proteins, and nucleic acids. Although the conditions used during electrospinning limit the already problematic viability/stability of such biological products, their effective incorporation into nanofibers has been shown to be feasible. Synthetic polymers have been more frequently applied to make nanofibers than natural polymers. Polymer blends are commonly used to achieve favorable physical properties of nanofibers. The majority of nanofibers that contain biological product have been designed for therapeutic applications. The incorporation of these biological products into nanofibers can promote their stability or viability, and also allow their delivery to a desired tissue or organ. Other applications include plant protection in agriculture, fermentation in the food industry, biocatalytic environmental remediation, and biosensing. Live cells that have been incorporated into nanofibers include bacteria and fungi. Nanofibers have served as scaffolds for stem cells seeded on a surface, to enable their delivery and application in tissue regeneration and wound healing. Viruses incorporated into nanofibers have been used in gene delivery, as well as in therapies against bacterial infections and cancers. Proteins (hormones, growth factors, and enzymes) and nucleic acids (DNA and RNA) have been incorporated into nanofibers, mainly to treat diseases and enhance their stability. To summarize, incorporation of biological products into nanofibers has numerous advantages, such as providing protection and facilitating controlled delivery from a solid form with a large surface area. Future studies should address the challenge of transferring nanofibers with biological products into practical and industrial use.

An Innovative Nanobody-Based Electrochemical Immunosensor Using Decorated Nylon Nanofibers for Point-of-Care Monitoring of Human Exposure to Pyrethroid Insecticides

A novel ultrasensitive nanobody-based electrochemical immunoassay was prepared for assessing human exposure to pyrethroid insecticides. 3-Phenoxybenzoic acid (3-PBA) is a common human urinary metabolite for numerous pyrethroids, which broadly served as a biomarker for following the human exposure to this pesticide group. The 3-PBA detection was via a direct competition for binding to alkaline phosphatase-embedded nanobodies between free 3-PBA and a 3-PBA-bovine serum albumin conjugate covalently immobilized onto citric acid-decorated nylon nanofibers, which were incorporated on a screen-printed electrode (SPE). Electrochemical impedance spectroscopy (EIS) was utilized to support the advantage of the employment of nanofibrous membranes and the success of the immunosensor assembly. The coupling between the nanofiber and nanobody technologies provided an ultrasensitive and selective immunosensor for 3-PBA detection in the range of 0.8 to 1000 pg mL-1 with a detection limit of 0.64 pg mL-1. Moreover, when the test for 3-PBA was applied to real samples, the established immunosensor proved to be a viable alternative to the conventional methods for 3-PBA detection in human urine even without sample cleanup. It showed excellent properties and stability over time.

Current Applications of Biopolymer-based Scaffolds and Nanofibers as Drug Delivery Systems

BACKGROUND

The high surface-to-volume ratio of polymeric nanofibers makes them an effective vehicle for the release of bioactive molecules and compounds such as growth factors, drugs, herbal extracts and gene sequences. Synthetic polymers are commonly used as sensors, reinforcements and energy storage, whereas natural polymers are more prone to mimicking an extracellular matrix. Natural polymers are a renewable resource and classified as an environmentally friendly material, which might be used in different techniques to produce nanofibers for biomedical applications such as tissue engineering, implantable medical devices, antimicrobial barriers and wound dressings, among others. This review sheds some light on the advantages of natural over synthetic polymeric materials for nanofiber production. Also, the most important techniques employed to produce natural nanofibers are presented. Moreover, some pieces of evidence regarding toxicology and cell-interactions using natural nanofibers are discussed. Clearly, the potential extrapolation of such laboratory results into human health application should be addressed cautiously.