Pediocin-like bacteriocins: new perspectives on mechanism of action and immunity

Innovative perspectives on bacteriocins: advances in classification, synthesis, mode of action, and food industry applications

Bacteriocins, natural antimicrobial peptides produced by bacteria, present eco-friendly, non-toxic, and cost-effective alternatives to traditional chemical antimicrobial agents in the food industry. This review provides a comprehensive update on the classification of bacteriocins in food preservation. It highlights the significant industrial potential of pediocin-like and two-peptide bacteriocins, emphasizing chemical synthesis methods like Fmoc-SPPS to meet the demand for bioactive bacteriocins. The review details the mode of action, focusing on mechanisms such as transmembrane potential disruption and pH-dependent effects. Furthermore, it addresses the limitations of bacteriocins in food preservation and explores the potential of nanotechnology-based encapsulation to enhance their antimicrobial efficacy. The benefits of nanoencapsulation, including improved stability, extended antimicrobial spectrum, and enhanced functionality, are underscored. This understanding is crucial for advancing the application of bacteriocins to ensure food safety and quality.

Antibacterial Mechanism of Garviecin LG34 Against S. Aureus and L. Monocytogenes and its Application in Milk Preservation

The objective of this study was to reveal the antibacterial mode of action of garviecin LG34 against S. aureus CICC 21600 and L. monocytogenes CICC 21633 and measure the inhibitions on these two foodborne pathogenic bacteria in milk. Antibacterial mechanism of garviecin LG34 was ascertained by its effect on the efflux of Potassium (K+) ions, extracellular electrical conductivity, UV-absorbing substances, potential across the membrane (ΔΨ), and cell permeability. The inhibition of garviecin LG34 against S. aureus CICC 21600 and L. monocytogenes CICC 21600 in milk was studied by viable counting method. Supplementation with 160 AU/ml of garviecin LG34 had a bactericidal effect on S. aureus CICC 21600 and L. monocytogenes CICC 21633. A total of 80, 160, and 320 AU/ml of garviecin LG34 resulted in the effusion of potassium ion and UV-absorbing substances, the leakage of cellular electrolytes, and the dissipation of electrical potential across the membrane of these two food-borne bacteria and showed a dose-dependent. Moreover, the increase in cell permeability of both strains was observed by flow cytometer after cells treated with 160 AU/ml of garviecin LG34. Garviecin LG34 significantly inhibited the growth of these two food-borne bacteria in milk, especially in skimmed milk. Garviecin LG34 could cause pore formation, intracellular materials release, and permeability increase of S. aureus CICC 21600 and L. monocytogenes CICC 21633, and could be applied to milk as bio-preservative.

Acidocin A and Acidocin 8912 Belong to a Distinct Subfamily of Class II Bacteriocins with a Broad Spectrum of Antimicrobial Activity

Within class II bacteriocins, we assume the presence of a separate subfamily of antimicrobial peptides possessing a broad spectrum of antimicrobial activity. Although these peptides are structurally related to the subclass IIa (pediocin-like) bacteriocins, they have significant differences in biological activities and, probably, a mechanism of their antimicrobial action. A representative of this subfamily is acidocin A from Lactobacillus acidophilus TK9201. We discovered the similarity between acidocin A and acidocin 8912 from Lactobacillus acidophilus TK8912 when analyzing plasmids from lactic acid bacteria and suggested the presence of a single evolutionary predecessor of these peptides. We obtained the C-terminally extended homolog of acidocin 8912, named acidocin 8912A, a possible intermediate form in the evolution of the former. The study of secondary structures and biological activities of these peptides showed their structural similarity to acidocin A; however, the antimicrobial activities of acidocin 8912 and acidocin 8912A were lower than that of acidocin A. In addition, these peptides demonstrated stronger cytotoxic and membranotropic effects. Building upon what we previously discovered about the immunomodulatory properties of acidocin A, we studied its proteolytic stability under conditions simulating those in the digestive tract and also assessed its ability to permeate intestinal epithelium using the Caco-2 cells monolayer model. In addition, we found a pronounced effect of acidocin A against fungi of the genus Candida, which might also expand the therapeutic potential of this bacterial antimicrobial peptide.

Emerging lactic acid bacteria bacteriocins as anti-cancer and anti-tumor agents for human health

Modern cancer diagnostics and treatment options have greatly improved survival rates; the illness remains a major cause of mortality worldwide. Current treatments for cancer, such as chemotherapy, are not cancer-specific and may cause harm to healthy cells; therefore, it is imperative that new drugs for cancer be developed that are both safe and effective. It has been found that lactic acid bacteria (LAB) have the potential to produce bacteriocins, which could potentially offer a promising alternative for cancer treatment. They have been shown in several studies to be effective against cancer cells while having no effect on healthy cells. More research is needed to fully understand the potential of LAB bacteriocins as anti-cancer medicines, to find the appropriate dose and delivery route, and to conduct clinical trials to evaluate the effectiveness and safety of the products in human patients, as is suggested by this work. Furthermore, LAB bacteriocins may evolve into a significant new class of anti-cancer drugs and food products. Patients with cancer may have a safe and effective alternative treatment option in the form of anti-cancer foods and drugs. Therefore, the aim of this study is to provide an in-depth analysis of the recent breakthroughs and potential future technical advancements of significant bacteriocins that are produced by LAB, how these bacteriocins function, and how these bacteriocins may be utilized as an anti-cancer agent. In addition, the current analysis emphasizes the significant constraints and boundaries that bacteriocins face when they are used as an anti-cancer factor.

Production of bacterial cellulose-based peptidopolysaccharide BC-L with anti-listerial properties using a co-cultivation strategy

Bacterial cellulose (BC) has been found extensive applications in diverse domains for its exceptional attributes. However, the lack of antibacterial properties hampers its utilization in food and biomedical sectors. Leucocin, a bacteriocin belonging to class IIa, is synthesized by Leuconostoc that demonstrates potent efficacy against the foodborne pathogen, Listeria monocytogenes. In the current study, co-culturing strategy involving Kosakonia oryzendophytica FY-07 and Leuconostoc carnosum 4010 was used to confer anti-listerial activity to BC, which resulted in the generation of leucocin-containing BC (BC-L). The physical characteristics of BC-L, as determined by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA), were similar to the physical characteristics of BC. Notably, the experimental results of disc diffusion and growth curve indicated that the BC-L film exhibited a potent inhibitory effect against L. monocytogenes. Scanning electron microscopy (SEM) showed that BC-L exerts its bactericidal activity by forming pores on the bacterial cell wall. Despite the BC-L antibacterial mechanism, which involves pore formation, the mammalian cell viability remained unaffected by the BC-L film. The measurement results of zeta potential indicated that the properties of BC changed after being loaded with leucocin. Based on these findings, the anti-listerial BC-L generated through this co-culture system holds promise as a novel effective antimicrobial agent for applications in meat product preservation and packaging.

Molecular Dynamic Study on the Structure and Thermal Stability of Mutant Pediocin PA-1 Peptides Engineered with Cysteine Substitutions

Pediocin and analogous bacteriocins, valued for thermal stability, serve as versatile antimicrobials in the food sector. Improving their resilience at high temperatures and deriving derivatives not only benefit food production but also offer broad-spectrum antimicrobial potential in pharmaceuticals, spanning treatments for peptic ulcers, women's health, and novel anticancer agents. The study aims to create mutant peptides capable of establishing a third disulfide bond or enhanced through cysteine substitutions. This involves introducing additional Cys residues into the inherent structure of pediocin PA-1 to facilitate disulfide bond formation. Five mutants (Mut 1-5) were systematically generated with double Cys substitutions and assessed for thermal stability through MD simulations across temperatures (298-394 K). The most robust mutants (Mut 1, Mut 4-5) underwent extended analysis via MD simulations, comparing their structural stability, secondary structure, and surface accessibility to the reference Pediocin PA-1 molecule. This comprehensive assessment aims to understand how Cys substitutions influence disulfide bonds and the overall thermal stability of the mutant peptides. In silico analysis indicated that Mut 1 and Mut 5, along with the reference structure, lose their helical structure and one natural disulfide bond at high temperatures, and may impacting antimicrobial activity. Conversely, Mut 4 retained its helical structure and exhibited thermal stability similar to Pediocin PA-1. Pending further experimental validation, this study implies Mut 4 may have high stability and exceptional resistance to high temperatures, potentially serving as an effective antimicrobial alternative.

Antimicrobial Activity of Synthetic Enterocins A, B, P, SEK4, and L50, Alone and in Combinations, against Clostridium perfringens

Multidrug-resistant Clostridium perfringens infections are a major threat to the poultry industry. Effective alternatives to antibiotics are urgently needed to prevent these infections and limit the spread of multidrug-resistant bacteria. The aim of the study was to produce by chemical synthesis a set of enterocins of different subgroups of class II bacteriocins and to compare their spectrum of inhibitory activity, either alone or in combination, against a panel of twenty C. perfringens isolates. Enterocins A, P, SEK4 (class IIa bacteriocins), B (unsubgrouped class II bacteriocin), and L50 (class IId leaderless bacteriocin) were produced by microwave-assisted solid-phase peptide synthesis. Their antimicrobial activity was determined by agar well diffusion and microtitration methods against twenty C. perfringens isolates and against other pathogens. The FICINDEX of different combinations of the selected enterocins was calculated in order to identify combinations with synergistic effects. The results showed that synthetic analogs of L50A and L50B were the most active against C. perfringens. These peptides also showed the broadest spectrum of activity when tested against other non-clostridial indicator strains, including Listeria monocytogenes, methicillin-resistant Staphylococcus aureus, Streptococcus suis, Streptococcus pyogenes, Enterococcus cecorum, Enterococcus faecalis, as well as Gram-negative bacteria (Campylobacter coli and Pseudomonas aeruginosa), among others. The selected synthetic enterocins were combined on the basis of their different mechanisms of action, and all combinations tested showed synergy or partial synergy against C. perfringens. In conclusion, because of their high activity against C. perfringens and other pathogens, the use of synthetic enterocins alone or as a consortium can be a good alternative to the use of antibiotics in the poultry sector.

Impact of bacteriocin-producing strains on bacterial community composition in a simplified human intestinal microbiota

Bacteriocins are antimicrobial peptides that have been studied for decades as food bio-preservatives or as alternatives to antibiotics. They also have potential as modulators of the gut microbiome, which has been linked to human health. However, it is difficult to predict a priori how bacteriocins will impact complex microbial communities through direct and indirect effects. Here we assess the effect of different bacteriocin-producing strains on a Simplified Human Intestinal Microbiota (SIHUMI) model, using a set of bacteriocin-producing strains (Bac+) and otherwise isogenic non-producers (Bac-). Bacteriocins from different classes and with different activity spectra were selected, including lantibiotics such as lacticin 3147 and nisin A, and pediocin-like bacteriocins such as pediocin PA-1 among other peptides. SIHUMI is a bacterial consortium of seven diverse human gut species that assembles to a predictable final composition in a particular growth medium. Each member can be individually tracked by qPCR. Bac+ and Bac- strains were superimposed on the SIHUMI system, and samples were taken at intervals up to 48 h. The genome copy number of each SIHUMI member was evaluated using specific primers. We establish that the composition of the community changes in response to the presence of either broad- or narrow-spectrum bacteriocin producers and confirm that there are significant off-target effects. These effects were analyzed considering antagonistic inter-species interactions within the SIHUMI community, providing a comprehensive insight into the possible mechanisms by which complex communities can be shaped by bacteriocins.

Natural Antimicrobials for Listeria monocytogenes in Ready-to-Eat Meats: Current Challenges and Future Prospects

Listeria monocytogenes, an intra-cellular, Gram-positive, pathogenic bacterium, is one of the leading agents of foodborne illnesses. The morbidity of human listeriosis is low, but it has a high mortality rate of approximately 20% to 30%. L. monocytogenes is a psychotropic organism, making it a significant threat to ready-to-eat (RTE) meat product food safety. Listeria contamination is associated with the food processing environment or post-cooking cross-contamination events. The potential use of antimicrobials in packaging can reduce foodborne disease risk and spoilage. Novel antimicrobials can be advantageous for limiting Listeria and improving the shelf life of RTE meat. This review will discuss the Listeria occurrence in RTE meat products and potential natural antimicrobial additives for controlling Listeria.

Nanomedicine for drug resistant pathogens and COVID-19 using mushroom nanocomposite inspired with bacteriocin – A Review

Multidrug resistant (MDR) pathogens have become a major global health challenge and have severely threatened the health of society. Current conditions have gotten worse as a result of the COVID-19 pandemic, and infection rates in the future will rise. It is necessary to design, respond effectively, and take action to address these challenges by investigating new avenues. In this regard, the fabrication of metal NPs utilized by various methods, including green synthesis using mushroom, is highly versatile, cost-effective, eco-compatible, and superior. In contrast, biofabrication of metal NPs can be employed as a powerful weapon against MDR pathogens and have immense biomedical applications. In addition, the advancement in nanotechnology has made possible to modify the nanomaterials and enhance their activities. Metal NPs with biomolecules composite to prevents their microbial adhesion and kills the microbial pathogens through biofilm formation. Bacteriocin is an excellent antimicrobial peptide that works well as an augmentation substance to boost the antimicrobial effects. As a result, we concentrate on the creation of new, eco-compatible mycosynthesized metal NPs with bacteriocin nanocomposite via electrostatic, covalent, or non-covalent bindings. The synergistic benefits of metal NPs with bacteriocin to combat MDR pathogens and COVID-19, as well as other biomedical applications, are discussed in this review. Moreover, the importance of the adverse outcome pathway (AOP) in risk analysis of manufactured metal nanocomposite nanomaterial and their future possibilities also discussed.

Structural Basis of the Mechanisms of Action and Immunity of Lactococcin A, a Class IId Bacteriocin

Lactococcin A (LcnA), a class IId bacteriocin, induces membrane leakage and cell death by specifically binding to the membrane receptor-mannose phosphotransferase system (man-PTS), as is the case for pediocin-like (class IIa) bacteriocins. The cognate immunity protein of bacteriocins, which protects the producer cell from its own bacteriocin, recognizes and binds to the bacteriocin-man-PTS complex, consequently blocking membrane leakage. We previously deciphered the mode of action and immunity of class IIa bacteriocins. Here, we determined the structure of the ternary complex of LcnA, LciA (i.e., the immunity protein), and its receptor, i.e., the man-PTS of Lactococcus lactis (ll-man-PTS). An external loop on the membrane-located component IIC of ll-man-PTS was found to prevent specific binding of the N-terminal region of LcnA to the site recognized by pediocin-like bacteriocins. Thus, the N-terminal β-sheet region of LcnA recognized an adjacent site on the extracellular side of ll-man-PTS, with the LcnA C-terminal hydrophobic helix penetrating into the membrane. The cytoplasmic cleft formed within the man-PTS Core and Vmotif domains induced by embedded LcnA from the periplasmic side is adopted by the appropriate angle between helices H3 and H4 of the N terminus of LciA. The flexible C terminus of LciA then blocks membrane leakage. To summarize, our findings reveal the molecular mechanisms of action and immunity of LcnA and LciA, laying a foundation for further design of class IId bacteriocins. IMPORTANCE Class IId (lactococcin-like) bacteriocins and class IIa (pediocin-like) bacteriocins share a few similarities: (i) both induce membrane leakage and cell death by specifically binding the mannose phosphotransferase system (man-PTS) on their target cells, and (ii) cognate immunity proteins recognize and bind to the bacteriocin-man-PTS complex to block membrane leakage. However, class IId bacteriocins lack the "pediocin box" motif, which is typical of class IIa bacteriocins, and basically target only lactococcal cells; in contrast, class IIa bacteriocins target diverse bacterial cells, but not lactococcal cells. We previously solved the structure of class IIa bacteriocin-receptor-immunity ternary complex from Lactobacillus sakei. Here, we determined the structure of the ternary complex of class IId bacteriocin LcnA, its cognate immunity protein LciA, and its receptor, the man-PTS of Lactococcus lactis. By comparing the interactions between man-PTS and class IIa and class IId bacteriocins, this study affords some clues to better understand the specificity of bacteriocins targeting the mannose phosphotransferase system.

High-efficiency production of the antimicrobial peptide pediocin PA-1 in metabolically engineered Corynebacterium glutamicum using a microaerobic process at acidic pH and elevated levels of bivalent calcium ions

BACKGROUND

Pediocin PA-1 is a bacteriocin of recognized value with applications in food bio-preservation and the medical sector for the prevention of infection. To date, industrial manufacturing of pediocin PA-1 is limited by high cost and low-performance. The recent establishment of the biotechnological workhorse Corynebacterium glutamicum as recombinant host for pediocin PA-1 synthesis displays a promising starting point towards more efficient production.

RESULTS

Here, we optimized the fermentative production process. Following successful simplification of the production medium, we carefully investigated the impact of dissolved oxygen, pH value, and the presence of bivalent calcium ions on pediocin production. It turned out that the formation of the peptide was strongly supported by an acidic pH of 5.7 and microaerobic conditions at a dissolved oxygen level of 2.5%. Furthermore, elevated levels of CaCl₂ boosted production. The IPTG-inducible producer C. glutamicum CR099 pXMJ19 P_tac pedACD^Cg provided 66 mg L^-1 of pediocin PA-1 in a two-phase batch process using the optimized set-up. In addition, the novel constitutive strain P_tuf pedACD^Cg allowed successful production without the need for IPTG.

CONCLUSIONS

The achieved pediocin titer surpasses previous efforts in various microbes up to almost seven-fold, providing a valuable step to further explore and develop this important bacteriocin. In addition to its high biosynthetic performance C. glutamicum proved to be highly robust under the demanding producing conditions, suggesting its further use as host for bacteriocin production.

Antimicrobial Activity and Immunomodulatory Properties of Acidocin A, the Pediocin-like Bacteriocin with the Non-Canonical Structure

Pediocin-like bacteriocins are among the natural antimicrobial agents attracting attention as scaffolds for the development of a new generation of antibiotics. Acidocin A has significant structural differences from most other members of this subclass. We studied its antibacterial and cytotoxic activity, as well as effects on the permeability of E. coli membranes in comparison with avicin A, the typical pediocin-like bacteriocin. Acidocin A had a more marked tendency to form an alpha-helical structure upon contact with detergent micelles, as was shown by CD spectroscopy, and demonstrated considerably less specific mode of action: it inhibited growth of Gram-positive and Gram-negative strains, which were unsusceptible to avicin A, and disrupted the integrity of outer and inner membranes of E. coli. However, the peptide retained a low toxicity towards normal and tumor human cells. The effect of mutations in the pediocin box of acidocin A (on average, a 2-4-fold decrease in activity) was less pronounced than is usually observed for such peptides. Using multiplex analysis, we showed that acidocin A and avicin A modulated the expression level of a number of cytokines and growth factors in primary human monocytes. Acidocin A induced the production of a number of inflammatory mediators (IL-6, TNFα, MIG/CXCL9, MCP-1/CCL2, MCP-3/CCL7, and MIP-1β) and inhibited the production of some anti-inflammatory factors (IL-1RA, MDC/CCL22). We assumed that the activity of acidocin A and similar peptides produced by lactic acid bacteria might affect the functional state of the human intestinal tract, not only through direct inhibition of various groups of symbiotic and pathogenic bacteria, but also via immunomodulatory effects.

Bacteriocin Production by Bacillus Species: Isolation, Characterization, and Application

Antibiotic resistance is a problem that has been increasing lately; therefore, it is important to find new alternatives to treat infections induced by pathogens that cannot be eliminated with available products. Small antimicrobial peptides (AMPs) known as bacteriocin could be an alternative to antibiotics because they have shown to be effective against a great number of multidrug-resistant microbes. In addition to its high specificity against microbial pathogens and its low cytotoxicity against human cells, most bacteriocin present tolerance to enzyme degradation and stability to temperature and pH alterations. Bacteriocins are small peptides with a great diversity of structures and functions; however, their mechanisms of action are still not well understood. In this review, bacteriocin produced by Bacillus species will be described, especially its mechanisms of action, culture conditions used to improve its production and state-of-the-art methodologies applied to identify them. Bacteriocin utilization as food preservatives and as new molecules to treat cancer also will be discussed.

Garvicin Q: characterization of biosynthesis and mode of action

Bacteriocins are ribosomally synthesized antimicrobial peptides, that either kill target bacteria or inhibit their growth. Bacteriocins are used in food preservation and are of increasing interest as potential alternatives to conventional antibiotics. In the present study, we show that Lactococcus petauri B1726, a strain isolated from fermented balsam pear, produces a heat-stable and protease-sensitive compound. Following genome sequencing, a gene cluster for production of a class IId bacteriocin was identified consisting of garQ (encoding for the bacteriocin garvicin Q), garI (for a putative immunity protein), garC, and garD (putative transporter proteins). Growth conditions were optimized for increased bacteriocin activity in supernatants of L. petauri B1726 and purification and mass spectrometry identified the compound as garvicin Q. Further experiments suggest that garvicin Q adsorbs to biomass of various susceptible and insusceptible bacteria and support the hypothesis that garvicin Q requires a mannose-family phosphotransferase system (PTS^Man) as receptor to kill target bacteria by disruption of membrane integrity. Heterologous expression of a synthetic garQICD operon was established in Corynebacterium glutamicum demonstrating that genes garQICD are responsible for biosynthesis and secretion of garvicin Q. Moreover, production of garvicin Q by the recombinant C. glutamicum strain was improved by using a defined medium yet product levels were still considerably lower than with the natural L. petauri B1726 producer strain.Collectively, our data identifies the genetic basis for production of the bacteriocin garvicin Q by L. petauri B1726 and provides insights into the receptor and mode of action of garvicin Q. Moreover, we successfully performed first attempts towards biotechnological production of this interesting bacteriocin using natural and heterologous hosts.

Structural Features, Mechanisms of Action, and Prospects for Practical Application of Class II Bacteriocins

Bacteriocins are antimicrobial peptides ribosomally synthesized by both Gram-negative and Gram-positive bacteria, as well as by archaea. Bacteriocins are usually active against phylogenetically related bacteria, providing competitive advantage to their producers in the natural bacterial environment. However, some bacteriocins are known to have a broader spectrum of antibacterial activity, including activity against multidrug-resistant bacterial strains. Multitude of bacteriocins studied to date are characterized by a wide variety of chemical structures and mechanisms of action. Existing classification systems for bacteriocins take into account structural features and biosynthetic pathways of bacteriocins, as well as the phylogenetic affiliation of their producing organisms. Heat-stable bacteriocins with molecular weight of less than 10 kDa from Gram-positive and Gram-negative producers are divided into post-translationally modified (class I) and unmodified peptides (class II). In recent years there has been an increasing interest in the class II bacteriocins as potential therapeutic agents that can help to combat antibiotic-resistant infections. Advantages of unmodified peptides are relative simplicity of their biotechnological production in heterologous systems and chemical synthesis. Potential for the combined use of bacteriocins with other antimicrobial agents allowing to enhance their efficacy, low probability of cross-resistance development, and ability of probiotic strains to produce bacteriocins in situ make them promising candidate compounds for creation of new drugs. The review focuses on structural diversity of the class II bacteriocins and their practical relevance.

The bacteriocin Angicin interferes with bacterial membrane integrity through interaction with the mannose phosphotransferase system

In a natural environment, bacteria are members of multispecies communities. To compete with rival species, bacteria produce antimicrobial peptides (AMPs), called bacteriocins. Bacteriocins are small, cationic, ribosomally synthesized peptides, which normally inhibit closely related species of the producing organism. Bacteriocin production is best studied in lactic bacteria (LAB). Streptococcus anginosus, belonging to LAB, produces the potent bacteriocin Angicin, which shows inhibitory activity against other streptococci, Listeria monocytogenes and vancomycin resistant Enterococcus faecium (VRE). Furthermore, Angicin shows a high resistance toward pH changes and heat, rendering it an interesting candidate for food preservation or clinical applications. The inhibitory activity of Angicin depends on the presence of a mannose phosphotransferase system (Man-PTS) in target cells, since L. monocytogenes harboring a deletion in an extracellular loop of this system is no longer sensitive to Angicin. Furthermore, we demonstrated by liposome leakage and pHluorin assays that Angicin destroys membrane integrity but shows only low cytotoxicity against human cell lines. In conclusion, we show that Angicin has a detrimental effect on the membrane of target organisms by using the Man-PTS as a receptor.

Structural Basis of the Immunity Mechanisms of Pediocin-like Bacteriocins

Pediocin-like bacteriocins, also designated class IIa bacteriocins, are ribosomally synthesized antimicrobial peptides targeting species closely related to the producers. They act on the cytoplasmic membrane of Gram-positive cells by dissipating the transmembrane electrical potential through pore formation with the mannose phosphotransferase system (man-PTS) as the target/receptor. Bacteriocin-producing strains also synthesize a cognate immunity protein that protects them against their own bacteriocins. Herein, we report the cryo-electron microscopy structure of the bacteriocin-receptor-immunity ternary complex from Lactobacillus sakei. The complex structure reveals that pediocin-like bacteriocins bind to the same position on the Core domain of man-PTS, while the C-terminal helical tails of bacteriocins delimit the opening range of the Core domain away from the Vmotif domain to facilitate transmembrane pore formation. Upon attack of bacteriocins from the extracellular side, man-PTS exposes its cytosolic side for recognition of the N-terminal four-helix bundle of the immunity protein. The C-terminal loop of the immunity protein then inserts into the pore and blocks leakage induced by bacteriocins. Elucidation of the toxicity and immunity mechanisms of pediocin-like bacteriocins could support the design of novel bacteriocins against antibiotic-resistant pathogenic bacteria. IMPORTANCE Pediocin-like bacteriocins, ribosomally synthesized antimicrobial peptides, are generally co-expressed with cognate immunity proteins to protect the bacteriocin-producing strain from its own bacteriocin. Bacteriocins are considered potential alternatives to conventional antibiotics in the context of the bacterial resistance crisis, but the immunity mechanism is unclear. This study uncovered the mechanisms of action and immunity of class IIa bacteriocins.

BIOTECHNOLOGICAL ASPECTS OF THE DEVELOPMENT OF A LIQUID FORMULATION OF MULTIFUNCTIONAL ENZYBIOTIC ANTISEPTIC

Aim. Evaluation of biotechnological aspects of the production of a liquid formulation of the multifunctional antiseptic preparation of microbial origin, which can be typified as an enzybiotic; characterization of the enzyme specificity of the studied formulation, stabilization methods, its ability to affect microbial biofilms. Methods. Gel-filtration and electrophoresis were used to study the component composition and the specificity of the enzyme complex of the Streptomyces albus UN 44 producer strain. Proteolytic and staphylolytic activities of individual fractions were determined. The Pseudomonas aeruginosa biofilm and its formation under the effect of various drug formulations were quantitatively evaluated by spectrophotometry. Results. The stability of the liquid formulation of the enzybiotic biosynthesized by S. albus UN 44 was demonstrated. Activity of the formulation could be prolonged and additionally stabilized by adding of 0.5% polyvinyl alcohol. Fractionation of the formulation enzyme complex using gel-filtration revealed the presence of at least three proteinases of different molecular weights (80-100, 24-35 and 20 kDa) and lysoenzymes (18-22 kDa). The effectiveness of the developed liquid antibiotic formulation for the destruction and inhibition (8-10 folds) of the biofilm formation by clinical strains of P. aeruginosa was shown. Conclusions. The broad spectrum, multidirectional mechanisms of antimicrobial and regenerative action of enzybiotic drug, and the possibility of its production directly from the biotechnological process determine the prospects of its manufacturing and use as a multifunctional surface antiseptic.

Novel pathways in bacteriocin synthesis by lactic acid bacteria with special reference to ethnic fermented foods

Ethnic fermented foods are known for their unique aroma, flavour, taste, texture and other sensory properties preferred by every ethnic community in this world culturally as parts of their eatables. Some beneficial microorganisms associated with fermented foods have several functional properties and health-promoting benefits. Bacteriocins are the secondary metabolites produced by the microorganisms mostly lactic acid bacteria present in the fermented foods which can act as lantibiotics against the pathogen bacteria. Several studies have been conducted regarding the isolation and characterization of potent strains as well as their association with different types of bacteriocins. Collective information regarding the gene organizations responsible for the potent effect of bacteriocins as lantibiotics, mode of action on pathogen bacterial cells is not yet available. This review focuses on the gene organizations, pathways include for bacteriocin and their mode of action for various classes of bacteriocins produced by lactic acid bacteria in some ethnic fermented foods.

Angicin, a novel bacteriocin of Streptococcus anginosus

As a conserved defense mechanism, many bacteria produce antimicrobial peptides, called bacteriocins, which provide a colonization advantage in a multispecies environment. Here the first bacteriocin of Streptococcus anginosus, designated Angicin, is described. S. anginosus is commonly described as a commensal, however it also possesses a high pathogenic potential. Therefore, understanding factors contributing to its host colonization and persistence are important. A radial diffusion assay was used to identify S. anginosus BSU 1211 as a potent bacteriocin producer. By genetic mutagenesis the background of bacteriocin production and the bacteriocin gene itself were identified. Synthetic Angicin shows high activity against closely related streptococci, listeria and vancomycin resistant enterococci. It has a fast mechanism of action and causes a membrane disruption in target cells. Angicin, present in cell free supernatant, is insensitive to changes in temperature from - 70 to 90 °C and pH values from 2 to 10, suggesting that it represents an interesting compound for potential applications in food preservation or clinical settings.

Structural basis of pore formation in the mannose phosphotransferase system (man-PTS) by pediocin PA-1

Bacteriocins are ribosomally synthesized bacterial antimicrobial peptides that have a narrow spectrum of antibacterial activity against species closely related to the producers. Pediocin-like (or class IIa) bacteriocins (PLBs) exhibit antibacterial activity against several Gram-positive bacterial strains by forming pores in the cytoplasmic membrane of target cells with the specific receptor, the mannose phosphotransferase system (man-PTS). In this study, we report the cryo-electron microscopy structures of man-PTS from Listeria monocytogenes alone and its complex with pediocin PA-1, the first and most extensively studied representative PLB at a resolution of 3.12 Å and 2.45 Å, respectively. The structures revealed that the binding of pediocin PA-1 opens the Core domain of man-PTS away from its Vmotif domain, creating a pore through the cytoplasmic membranes of target cells. During this process, the N-terminal β-sheet region of pediocin PA-1 can specifically attach to the extracellular surface of the man-PTS Core domain, whereas the C-terminal half penetrates the membrane and cracks the man-PTS like a wedge. Thus, our findings shed light on a design of novel PLBs that can kill target pathogenic bacteria. Importance Listeria monocytogenes is a ubiquitous microorganism responsible for listeriosis, a rare but severe disease in humans who become infected by ingesting contaminated food products (i.e., dairy, meat, fish, and vegetables), which have a fatality rate of 33%. Pediocin PA-1 is an important commercial additive used in food production to inhibit Listeria species. The mannose phosphotransferase system (man-PTS) is responsible for the sensitivity of Listeria monocytogenes to pediocin PA-1. In this study, we report the cryo-EM structures of man-PTS from Listeria monocytogenes alone and its complex with pediocin PA-1 at a resolution of 3.12 Å and 2.45 Å, respectively. Our results facilitate the understanding of the mode of action of class IIa bacteriocins as an alternative to antibiotics.

Ribosomally synthesized peptides, foreground players in microbial interactions: recent developments and unanswered questions

It is currently well established that multicellular organisms live in tight association with complex communities of microorganisms including a large number of bacteria. These are immersed in complex interaction networks reflecting the relationships established between them and with host organisms; yet, little is known about the molecules and mechanisms involved in these mutual interactions. Ribosomally synthesized peptides, among which bacterial antimicrobial peptides called bacteriocins and microcins have been identified as contributing to host-microbe interplays, are either unmodified or post-translationally modified peptides. This review will unveil current knowledge on these ribosomal peptide-based natural products, their interplay with the host immune system, and their roles in microbial interactions and symbioses. It will include their major structural characteristics and post-translational modifications, the main rules of their maturation pathways, and the principal ecological functions they ensure (communication, signalization, competition), especially in symbiosis, taking select examples in various organisms. Finally, we address unanswered questions and provide a framework for deciphering big issues inspiring future directions in the field.

Ubericin K, a New Pore-Forming Bacteriocin Targeting mannose-PTS

Bovine mastitis infection in dairy cattle is a significant economic burden for the dairy industry globally. To reduce the use of antibiotics in treatment of clinical mastitis, new alternative treatment options are needed. Antimicrobial peptides from bacteria, also known as bacteriocins, are potential alternatives for combating mastitis pathogens. In search of novel bacteriocins against mastitis pathogens, we screened samples of Norwegian bovine raw milk and found a Streptococcus uberis strain with potent antimicrobial activity toward Enterococcus, Streptococcus, Listeria, and Lactococcus. Whole-genome sequencing of the strain revealed a multibacteriocin gene cluster encoding one class IIb bacteriocin, two class IId bacteriocins, in addition to a three-component regulatory system and a dedicated ABC transporter. Isolation and purification of the antimicrobial activity from culture supernatants resulted in the detection of a 6.3-kDa mass peak by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry, a mass corresponding to the predicted size of one of the class IId bacteriocins. The identification of this bacteriocin, called ubericin K, was further confirmed by in vitro protein synthesis, which showed the same inhibitory spectrum as the purified antimicrobial compound. Ubericin K shows highest sequence similarity to the class IId bacteriocins bovicin 255, lactococcin A, and garvieacin Q. We found that ubericin K uses the sugar transporter mannose phosphotransferase (PTS) as a target receptor. Further, by using the pHlourin sensor system to detect intracellular pH changes due to leakage across the membrane, ubericin K was shown to be a pore former, killing target cells by membrane disruption. IMPORTANCE Bacterial infections in dairy cows are a major burden to farmers worldwide because infected cows require expensive treatments and produce less milk. Today, infected cows are treated with antibiotics, a practice that is becoming less effective due to antibiotic resistance. Compounds other than antibiotics also exist that kill bacteria causing infections in cows; these compounds, known as bacteriocins, are natural products produced by other bacteria in the environment. In this work, we discover a new bacteriocin that we call ubericin K, which kills several species of bacteria known to cause infections in dairy cows. We also use in vitro synthesis as a novel method for rapidly characterizing bacteriocins directly from genomic data, which could be useful for other researchers. We believe that ubericin K and the methods described in this work will aid in the transition away from antibiotics in the dairy industry.

Current Knowledge of the Mode of Action and Immunity Mechanisms of LAB-Bacteriocins

Bacteriocins produced by lactic acid bacteria (LAB-bacteriocins) may serve as alternatives for aging antibiotics. LAB-bacteriocins can be used alone, or in some cases as potentiating agents to treat bacterial infections. This approach could meet the different calls and politics, which aim to reduce the use of traditional antibiotics and develop novel therapeutic options. Considering the clinical applications of LAB-bacteriocins as a reasonable and desirable therapeutic approach, it is therefore important to assess the advances achieved in understanding their modes of action, and the resistance mechanisms developed by the producing bacteria to their own bacteriocins. Most LAB-bacteriocins act by disturbing the cytoplasmic membrane through forming pores, or by cell wall degradation. Nevertheless, some of these peptides still have unknown modes of action, especially those that are active against Gram-negative bacteria. Regarding immunity, most bacteriocin-producing strains have an immunity mechanism involving an immunity protein and a dedicated ABC transporter system. However, these immunity mechanisms vary from one bacteriocin to another.

Establishing recombinant production of pediocin PA-1 in Corynebacterium glutamicum

Bacteriocins are antimicrobial peptides produced by bacteria to inhibit competitors in their natural environments. Some of these peptides have emerged as commercial food preservatives and, due to the rapid increase in antibiotic resistant bacteria, are also discussed as interesting alternatives to antibiotics for therapeutic purposes. Currently, commercial bacteriocins are produced exclusively with natural producer organisms on complex substrates and are sold as semi-purified preparations or crude fermentates. To allow clinical application, efficacy of production and purity of the product need to be improved. This can be achieved by shifting production to recombinant microorganisms.

Here, we identify Corynebacterium glutamicum as a suitable production host for the bacteriocin pediocin PA-1. C. glutamicum CR099 shows resistance to high concentrations of pediocin PA-1 and the bacteriocin was not inactivated when spiked into growing cultures of this bacterium. Recombinant C. glutamicum expressing a synthetic pedACD^Cgl operon releases a compound that has potent antimicrobial activity against Listeria monocytogenes and Listeria innocua and matches size and mass:charge ratio of commercial pediocin PA-1. Fermentations in shake flasks and bioreactors suggest that low levels of dissolved oxygen are favorable for production of pediocin. Under these conditions, however, reduced activity of the TCA cycle resulted in decreased availability of the important pediocin precursor l-asparagine suggesting options for further improvement. Overall, we demonstrate that C. glutamicum is a suitable host for recombinant production of bacteriocins of the pediocin family.

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C. glutamicum CR099 is resistant to high concentrations of pediocin PA-1.

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Recombinant C. glutamicum CR099/pEKEx-pedACDCg produces of a compound with antimicrobial activity against Listeria sp.

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The purified compound matches size and mass:charge ratio of commercial pediocin PA-1.

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Low oxygen levels are favorable for production of active pediocin by C. glutamicum in batch fermentations.

Adaptive Response of Listeria monocytogenes to the Stress Factors in the Food Processing Environment

Listeria monocytogenes are Gram-positive, facultatively anaerobic, non-spore-forming bacteria that easily adapt to changing environmental conditions. The ability to grow at a wide range of temperatures, pH, and salinity determines the presence of the pathogen in water, sewage, soil, decaying vegetation, and animal feed. L. monocytogenes is an etiological factor of listeriosis, especially dangerous for the elderly, pregnant women, and newborns. The major source of L. monocytogenes for humans is food, including fresh and smoked products. Its high prevalence in food is associated with bacterial adaptation to the food processing environment (FPE). Since the number of listeriosis cases has been progressively increasing an efficient eradication of the pathogen from the FPE is crucial. Understanding the mechanisms of bacterial adaptation to environmental stress will significantly contribute to developing novel, effective methods of controlling L. monocytogenes in the food industry.

Mechanisms of action of ribosomally synthesized and posttranslationally modified peptides (RiPPs)

Natural products remain a critical source of medicines and drug leads. One of the most rapidly growing superclasses of natural products is RiPPs: ribosomally synthesized and posttranslationally modified peptides. RiPPs have rich and diverse bioactivities. This review highlights examples of the molecular mechanisms of action that underly those bioactivities. Particular emphasis is placed on RiPP/target interactions for which there is structural information. This detailed mechanism of action work is critical toward the development of RiPPs as therapeutics and can also be used to prioritize hits in RiPP genome mining studies.

Nosocomial Infections: Pathogenicity, Resistance and Novel Antimicrobials

Background. The fight against the spread of infectious diseases creates the problem of resistance to pathogens and the most resistant of them – the propagators of nosocomial infections – are formed in hospitals because of a number of reasons. The solution of the problem lies in different areas, but the search of new effective means for the treatment of such diseases remains relevant right today. The shortest way to do this is to find the "pain points" of the pathogens themselves, i.e. the factors of their pathogenicity and resistance to which the action of novel antiseptics should be directed. Objective. We aimed to analyse and evaluate the main factors of pathogenicity and resistance of pathogens of nosocomial infections to determine modern approaches to the development of novel antimicrobials. Methods. Search and systematization of new scientific data and results concerning pathogenic factors of microbial pathogens that can be used as targets for the action of drugs. Results. Over the last 10–20 years, due to the development of new research methods in biology, it has become possible to clarify the features and additional conditions for the detection of pathogenic factors of nosocomial infections. Additional mechanisms of manifestation of resistance, adhesiveness, invasiveness, transmission of signs, secretion of toxins by pathogens are shownthat determines the general increase of their resistance to the action of currently used means. The general idea of ​​creating antiseptics that will not increase the resistance of pathogens can now be implemented by using substances with multidirectional or indirect mechanisms of action that minimally affect the metabolism of the cell and significantly reduce its resistance and pathogenicity. Conclusions. Factors of pathogenicity of propagators of nosocomial infections and mechanisms of their implementation can be considered as the main targets for the action of novel antiseptics that will inhibit the spread of pathogens without increasing their resistance. The promising substances for such drugs, among other things, are bacteriophages and their modifications, enzybiotics, immunobiotics, autoinducer inhibitors, quorum sensing-system inhibitors, b-lactamase inhibitors and others. Some of these substances in combination with the new generation of antibiotics significantly enhance their effectiveness and together they are able to overcome the resistance of even multidrug-resistant pathogens.

High-pressure processing-induced transcriptome response during recovery of Listeria monocytogenes

Background

High-pressure processing (HPP) is a commonly used technique in the food industry to inactivate pathogens, including L. monocytogenes. It has been shown that L. monocytogenes is able to recover from HPP injuries and can start to grow again during long-term cold storage. To date, the gene expression profiling of L. monocytogenes during HPP damage recovery at cooling temperature has not been studied. In order identify key genes that play a role in recovery of the damage caused by HPP treatment, we performed RNA-sequencing (RNA-seq) for two L. monocytogenes strains (barotolerant RO15 and barosensitive ScottA) at nine selected time points (up to 48 h) after treatment with two pressure levels (200 and 400 MPa).

Results

The results showed that a general stress response was activated by SigB after HPP treatment. In addition, the phosphotransferase system (PTS; mostly fructose-, mannose-, galactitol-, cellobiose-, and ascorbate-specific PTS systems), protein folding, and cobalamin biosynthesis were the most upregulated genes during HPP damage recovery. We observed that cell-division-related genes (divIC, dicIVA, ftsE, and ftsX) were downregulated. By contrast, peptidoglycan-synthesis genes (murG, murC, and pbp2A) were upregulated. This indicates that cell-wall repair occurs as a part of HPP damage recovery. We also observed that prophage genes, including anti-CRISPR genes, were induced by HPP. Interestingly, a large amount of RNA-seq data (up to 85%) was mapped to Rli47, which is a non-coding RNA that is upregulated after HPP. Thus, we predicted that Rli47 plays a role in HPP damage recovery in L. monocytogenes. Moreover, gene-deletion experiments showed that amongst peptidoglycan biosynthesis genes, pbp2A mutants are more sensitive to HPP.

Conclusions

We identified several genes and mechanisms that may play a role in recovery from HPP damage of L. monocytogenes. Our study contributes to new information on pathogen inactivation by HPP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07407-6.

Heterologous Expression of the Leuconostoc Bacteriocin Leucocin C in Probiotic Yeast Saccharomyces boulardii

The yeast Saccharomyces boulardii is well known for its probiotic effects such as treating or preventing gastrointestinal diseases. Due to its ability to survive in stomach and intestine, S. boulardii could be applied as a vehicle for producing and delivering bioactive substances of interest to human gut. In this study, we cloned the gene lecC encoding the antilisterial peptide leucocin C from lactic acid bacterium Leuconostoc carnosum in S. boulardii. The constructed S. boulardii strain secreted a peptide, which had molecular weight corresponding to leucocin C in SDS-PAGE. The peptide band inhibited Listeria monocytogenes in gel overlay assay. Likewise, concentrated S. boulardii culture supernatant inhibited the growth of L. monocytogenes. The growth profile and acid tolerance of the leucocin C secreting S. boulardii were similar as those of the strain carrying the empty vector. We further demonstrated that the cells of the leucocin C producing S. boulardii efficiently killed L. monocytogenes, also without antibiotic selection pressure. These results showed that antilisterial activity could be added to the arsenal of probiotic activities of S. boulardii, demonstrating its potential as a carrier for therapeutics delivery.

The mannose phosphotransferase system (Man-PTS) - Mannose transporter and receptor for bacteriocins and bacteriophages

Mannose transporters constitute a superfamily (Man-PTS) of the Phosphoenolpyruvate Carbohydrate Phosphotransferase System (PTS). The membrane complexes are homotrimers of protomers consisting of two subunits, IIC and IID. The two subunits without recognizable sequence similarity assume the same fold, and in the protomer are structurally related by a two fold pseudosymmetry axis parallel to membrane-plane (Liu et al. (2019) Cell Research 29 680). Two reentrant loops and two transmembrane helices of each subunit together form the N-terminal transport domain. Two three-helix bundles, one of each subunit, form the scaffold domain. The protomer is stabilized by a helix swap between these bundles. The two C-terminal helices of IIC mediate the interprotomer contacts. PTS occur in bacteria and archaea but not in eukaryotes. Man-PTS are abundant in Gram-positive bacteria living on carbohydrate rich mucosal surfaces. A subgroup of IICIID complexes serve as receptors for class IIa bacteriocins and as channel for the penetration of bacteriophage lambda DNA across the inner membrane. Some Man-PTS are associated with host-pathogen and -symbiont processes.

Mining and Statistical Modeling of Natural and Variant Class IIa Bacteriocins Elucidate Activity and Selectivity Profiles across Species

Class IIa bacteriocin antimicrobial peptides (AMPs) are a compelling alternative to current antimicrobials because of potential specific activity toward antibiotic-resistant bacteria, including vancomycin-resistant enterococci. Engineering of these molecules would be enhanced by a better understanding of AMP sequence-activity relationships to improve efficacy in vivo and limit effects of off-target activity. Toward this goal, we experimentally evaluated 210 natural and variant class IIa bacteriocins for antimicrobial activity against six strains of enterococci. Inhibitory activity was ridge regressed to AMP sequence to predict performance, achieving an area under the curve of 0.70 and demonstrating the potential of statistical models for identifying and designing AMPs. Active AMPs were individually produced and evaluated against eight enterococcus strains and four Listeria strains to elucidate trends in susceptibility. It was determined that the mannose phosphotransferase system (manPTS) sequence is informative of susceptibility to class IIa bacteriocins, yet other factors, such as membrane composition, also contribute strongly to susceptibility. A broadly potent bacteriocin variant (lactocin DT1) from a Lactobacillus ruminis genome was identified as the only variant with inhibitory activity toward all tested strains, while a novel enterocin variant (DT2) from an Enterococcus faecium genome demonstrated specificity toward Listeria strains. Eight AMPs were evaluated for proteolytic stability to trypsin, chymotrypsin, and pepsin, and three C-terminal disulfide-containing variants, including divercin V41, were identified as compelling for future in vivo studies, given their high potency and proteolytic stability.IMPORTANCE Class IIa bacteriocin antimicrobial peptides (AMPs), an alternative to traditional small-molecule antibiotics, are capable of selective activity toward various Gram-positive bacteria, limiting negative side effects associated with broad-spectrum activity. This selective activity is achieved through targeting of the mannose phosphotransferase system (manPTS) of a subset of Gram-positive bacteria, although factors affecting this mechanism are not entirely understood. Peptides identified from genomic data, as well as variants of previously characterized AMPs, can offer insight into how peptide sequence affects activity and selectivity. The experimental methods presented here identify promising potent and selective bacteriocins for further evaluation, highlight the potential of simple computational modeling for prediction of AMP performance, and demonstrate that factors beyond manPTS sequence affect bacterial susceptibility to class IIa bacteriocins.

Broadening and Enhancing Bacteriocins Activities by Association with Bioactive Substances

Bacteriocins are antimicrobial peptides some of which are endowed with antiviral, anticancer and antibiofilm properties. These properties could be improved through synergistic interactions of these bacteriocins with other bioactive molecules such as antibiotics, phages, nanoparticles and essential oils. A number of studies are steadily reporting the effects of these combinations as new and potential therapeutic strategies in the future, as they may offer many incentives over existing therapies. In particular, bacteriocins can benefit from combination with nanoparticles which can improve their stability and solubility, and protect them from enzymatic degradation, reduce their interactions with other molecules and improve their bioavailability. Furthermore, the combination of bacteriocins with other antimicrobials is foreseen as a way to reduce the development of antibiotic resistance due to the involvement of several modes of action. Another relevant advantage of these synergistic combinations is that it decreases the concentration of each antimicrobial component, thereby reducing their side effects such as their toxicity. In addition, combination can extend the utility of bacteriocins as antiviral or anticancer agents. Thus, in this review, we report and discuss the synergistic effects of bacteriocin combinations as medicines, and also for other diverse applications including, antiviral, antispoilage, anticancer and antibiofilms.

BacSJ-Another Bacteriocin with Distinct Spectrum of Activity that Targets Man-PTS

Lactic acid bacteria produce diverse antimicrobial peptides called bacteriocins. Most bacteriocins target sensitive bacteria by binding to specific receptors. Although a plethora of bacteriocins have been identified, for only a few of them the receptors they recognize are known. Here, we identified permease IIC and surface protein IID, two membrane subunits of the mannose-specific quaternary phosphotransferase system (Man-PTS), as a receptor for BacSJ, a subclass IId bacteriocin produced by Lactobacillus paracasei subsp. paracasei BGSJ2-8. BacSJ shares 45% identity with another Man-PTS binding bacteriocin, garvicin Q (GarQ). Similarly to GarQ, BacSJ has a relatively broad activity spectrum acting against several Gram-positive bacteria, such as Lactococcus lactis and Listeria monocytogenes, harboring fairly similar Man-PTSs, but not against Lactococcus garvieae. To identify specific Man-PTS amino acids responsible for the L.lactis sensitivity to BacSJ, and thus likely involved in the interaction with this bacteriocin, we generated eight independent BacSJ resistant L.lactis mutants harboring five distinct missense mutations in the ptnC or ptnD genes encoding the IIC and IID subunits. Concurrently with the resistance to BacSJ, the mutants efficiently utilized mannose as a carbon source, which indicated functionality of their mutated Man-PTS. The amino acid substitutions in the mutants localized to the intracellular region of the IIC permease or to the extracellular parts of IID. This localization coincides with regions targeted by GarQ and some other Man-PTS-binding garvicins, pointing to similarities between all these bacteriocins in the mechanism of their interaction with Man-PTS. During the attack by these bacteriocins, subunits IID and IIC are assumed to function sequentially as a docking and an entry module allowing the toxic peptide to bind the cell and then open the pore. However, since not all of the BacSJ-resistant mutants exhibited cross-resistance to GarQ, we propose that BacSJ interacts with Man-PTS in a manner slightly different from that of GarQ.

Comparative Genomics of the Transport Proteins of Ten Lactobacillus Strains

The genus Lactobacillus includes species that may inhabit different anatomical locations in the human body, but the greatest percentage of its species are inhabitants of the gut. Lactobacilli are well known for their probiotic characteristics, although some species may become pathogenic and exert negative effects on human health. The transportome of an organism consists of the sum of the transport proteins encoded within its genome, and studies on the transportome help in the understanding of the various physiological processes taking place in the cell. In this communication we analyze the transport proteins and predict probable substrate specificities of ten Lactobacillus strains. Six of these strains (L. brevis, L. bulgaricus, L. crispatus, L. gasseri, L. reuteri, and L. ruminis) are currently believed to be only probiotic (OP). The remaining four strains (L. acidophilus, L. paracasei, L. planatarum, and L. rhamnosus) can play dual roles, being both probiotic and pathogenic (PAP). The characteristics of the transport systems found in these bacteria were compared with strains (E. coli, Salmonella, and Bacteroides) from our previous studies. Overall, the ten lactobacilli contain high numbers of amino acid transporters, but the PAP strains contain higher number of sugar, amino acid and peptide transporters as well as drug exporters than their OP counterparts. Moreover, some of the OP strains contain pore-forming toxins and drug exporters similar to those of the PAP strains, thus indicative of yet unrecognized pathogenic potential. The transportomes of the lactobacilli seem to be finely tuned according to the extracellular and probiotic lifestyles of these organisms. Taken together, the results of this study help to reveal the physiological and pathogenic potential of common prokaryotic residents in the human body.

Synergistic inhibition mechanism of pediocin PA-1 and L-lactic acid against Aeromonas hydrophila

Pediocin PA-1 (PA-1) is a membrane-targeting bacteriocin from lactic acid bacteria, which shows antimicrobial activity against a wide range of Gram-positive pathogens. However, the outer membrane of Gram-negative bacteria does not allow pediocin access to its target. In this work, the synergistic inhibitory mechanism of PA-1 with L-lactic acid against Gram-negative aquaculture and food pathogen Aeromonas hydrophila (A. hydrophila) was analyzed. The combined treatment of 3.5 mmol/L L-lactic acid and 50 μmol/L (or 30 μmol/L) PA-1 had strong bacteriostatic and bactericidal activity against A. hydrophila. Full wavelength scanning and ELISA assay revealed the release of lipopolysaccharide (LPS) from the outer membrane of A. hydrophila caused by L-lactic acid treatment. Laser confocal microscopic imaging of A. hydrophila with FITC-labeled pediocin PA-1 proved the accumulation of PA-1 on lactic acid-treated bacterial cells. PA-1 then caused a rapid dissipation of membrane potential (Δψ) and a proton gradient difference (ΔpH) in lactic acid-treated A. hydrophila. Pediocin PA-1 also caused an increase in the extracellular ATP level. Morphology revealed by SEM and TEM showed that combined treating with lactic acid and PA-1 induced vesicles on the cell surface, the outer and inner membrane disruption, and even cytoplasm leakage and cell lysis. The results proved a potential mechanism of the synergistic inhibition of lactic acid and PA-1 against A. hydrophila, by which L-lactic acid released the outer membrane LPS, making it possible for PA-1 to contact the plasma membrane of A. hydrophila, resulting in the dissipation of proton-motive force in the inner membrane and cell death.

Features and applications of Ent35-MccV hybrid bacteriocin: current state and perspectives

Bacteriocins are peptides of ribosomal synthesis that are active against bacteria related to the producing strain. They have been widely used in the food industry as biopreservatives. The generation of hybrid peptides by combining the genes that encode two different bacteriocins has made it possible to study the mechanisms of action of the bacteriocins that compose them and also develop new peptides with improved biotechnological applications. Hybrid bacteriocins may be obtained in several ways. In our laboratory, by combining enterocin CRL35 and microcin V (Ent35-MccV), we obtained a broad-spectrum peptide that is active against both Gram-positive and Gram-negative bacteria. Ent35-MccV is sensitive to the action of intestinal proteases and is heat resistant, which makes it a good candidate for use as a biopreservative. For this reason, the peptide was tested in skim milk and beef burgers as food models. We also obtained more potent variants of the hybrid by modifying the central amino acid of the hinge region that connects the two bacteriocins. This review also discusses future applications and perspectives regarding the Ent35-MccV and other hybrid peptides.Key Points• Ent35-MccV is a new broad-spectrum bacteriocin.• The mechanism of action of bacteriocins can be studied using hybrid peptides.• Genetic engineering allows obtaining improved bacteriocin derivatives.• Hybrid peptides can be used in the food, pharmaceutical, and veterinary applications.

Transporters of glucose and other carbohydrates in bacteria

Glucose arguably is the most important energy carrier, carbon source for metabolites and building block for biopolymers in all kingdoms of life. The proper function of animal organs and tissues depends on the continuous supply of glucose from the bloodstream. Most animals can resorb only a small number of monosaccharides, mostly glucose, galactose and fructose, while all other sugars oligosaccharides and dietary fibers are degraded and metabolized by the microbiota of the lower intestine. Bacteria, in contrast, are omnivorous. They can import and metabolize structurally different sugars and, as a consortium of different species, utilize almost any sugar, sugar derivative and oligosaccharide occurring in nature. Bacteria have membrane transport systems for the uptake of sugars against steep concentration gradients energized by ATP, the proton motive force and the high energy glycolytic intermediate phosphoenolpyruvate (PEP). Different uptake mechanisms and the broad range of overlapping substrate specificities allow bacteria to quickly adapt to and colonize changing environments. Here, we review the structures and mechanisms of bacterial representatives of (i) ATP-dependent cassette (ABC) transporters, (ii) major facilitator (MFS) superfamily proton symporters, (iii) sodium solute symporters (SSS) and (iv) enzyme II integral membrane subunits of the bacterial PEP-dependent phosphotransferase system (PTS). We give a short overview on the distribution of transporter genes and their phylogenetic relationship in different bacterial species. Some sugar transporters are hijacked for import of bacteriophage DNA and antibacterial toxins (bacteriocins) and they facilitate the penetration of polar antibiotics. Finally, we describe how the expression and activity of certain sugar transporters are controlled in response to the availability of sugars and how the presence and uptake of sugars may affect pathogenicity and host-microbiota interactions.

The Man-PTS subunit ⅡC is responsible for the sensitivity of Listeria monocytogenes to durancin GL

Target cell recognition is an important issue in the realization of bacteriocin's activity. In this report, we provide genetic and biochemical evidence of durancin GL, a new bacteriocin produced by Enterococcus durans 41D, and use ⅡC subunit in the mannose phosphotransferase system (Man-PTS) of Listeria monocytogenes as target/receptor. First, the L. monocytogenes mutants with Man-PTS IIC or IID deletion were constructed with the vector pHoss1. Then, the utilization of glucose and mannose and the sensitivity to durancin GL of the mutant strains were investigated. Afterward, the interactions between durancin GL and the subunits of IIC or IID in Man-PTS of L. monocytogenes were characterized by yeast two-hybrid system. The results showed that the L. monocytogenes mutants with either IIC or IID deletion were not only resistant to durancin GL, but also their absorption and utilization of glucose and mannose were not disturbed by the presence of durancin GL. Finally, in situ detection of the interaction between durancin GL and Man-PTS subunits of IIC or IID by yeast two-hybrid system revealed that there was a strong interaction between durancin GL and Man-PTS subunit IIC. However, the interaction between durancin GL and Man-PTS subunit IID was not present or weak. Based on the experimental evidence above, the Man-PTS subunit IIC is responsible for the sensitivity of L. monocytogenes to bacteriocin durancin GL.

Obtaining an Ent35-MccV derivative with mutated hinge region that exhibits increased activity against Listeria monocytogenes and Escherichia coli

The present paper describes the generation of derivatives from the hybrid peptide called Ent35-MccV, active against Gram-positive and Gram-negative bacteria. This peptide has a triple glycine hinge region between enterocin CRL35 and microcin V. In order to obtain variants of Ent35-MccV with greater biotechnological potential, a saturation mutagenesis was carried out in the hinge region. As a result, we obtained a bank of E. coli strains expressing different mutated hybrid bacteriocins in the central position of the hinge region. From all these variants, we found that the one bearing a tyrosine in the central region of the hinge (Ent35-GYG-MccV) is 2-fold more active against E. coli and 4-fold more active against Listeria than the original peptide Ent35-MccV. This derivative was purified and characterized. The development and evaluation of alternative hinges for Ent35-MccV represents a step forward in the bioengineering of antimicrobial peptides. This approach fosters the rational design of peptides with enhanced antimicrobial activity.

Pediocin-Like Antimicrobial Peptides of Bacteria

Bacteriocins are bacterial antimicrobial peptides that, unlike classical peptide antibiotics, are products of ribosomal synthesis and usually have a narrow spectrum of antibacterial activity against species closely related to the producers. Pediocin-like bacteriocins (PLBs) belong to the class IIa of the bacteriocins of Gram-positive bacteria. PLBs possess high activity against pathogenic bacteria from Listeria and Enterococcus genera. Molecular target for PLBs is a membrane protein complex - bacterial mannose-phosphotransferase. PLBs can be synthesized by components of symbiotic microflora and participate in the maintenance of homeostasis in various compartments of the digestive tract and on the surface of epithelial tissues contacting the external environment. PLBs could give a rise to a new group of antibiotics of narrow spectrum of activity.

Enterococci: Between Emerging Pathogens and Potential Probiotics

Enterococci are ubiquitous microorganisms that could be found everywhere; in water, plant, soil, foods, and gastrointestinal tract of humans and animals. They were previously used as starters in food fermentation due to their biotechnological traits (enzymatic and proteolytic activities) or protective cultures in food biopreservation due to their produced antimicrobial bacteriocins called enterocins or as probiotics, live cells with different beneficial characteristics such as stimulation of immunity, anti-inflammatory activity, hypocholesterolemic effect, and prevention/treatment of some diseases. However, in the last years, the use of enterococci in foods or as probiotics caused an important debate because of their opportunistic pathogenicity implicated in several nosocomial infections due to virulence factors and antibiotic resistance, particularly the emergence of vancomycin-resistant enterococci. These virulence traits of some enterococci are associated with genetic transfer mechanisms. Therefore, the development of new enterococcal probiotics needs a strict assessment with regard to safety aspects for selecting the truly harmless enterococcal strains for safe applications. This review tries to give some data of the different points of view about this question.

Biotechnological Method of Preparation and Characterization of Recombinant Antimicrobial Peptide Avicin A from Enterococcus avium

Avicin A is a bacteriocin from the gram-positive bacterium Enterococcus avium. It exhibits a high microbicidal activity against bacteria of the genus Listeria, a causative agent of the severe human infection listeriosis. We developed a biotechnological method for obtaining avicin A and characterized its structure and biological activity. We also proposed a possible mechanism of the antimicrobial action of avicin A.

Intracellular pHluorin as Sensor for Easy Assessment of Bacteriocin-Induced Membrane-Damage in Listeria monocytogenes

Bacteriocins are antimicrobial peptides naturally produced by many bacteria and were shown to be effective against various pathogens including Listeria monocytogenes. L. monocytogenes is a food-borne pathogen that frequently causes disease outbreaks around the world with fatal outcomes in at-risk individuals. Thus, bacteriocins are a promising solution to prevent contaminations with L. monocytogenes and other microorganisms during food production and preservation. In the present study, we constructed L. monocytogenes EGD-e/pNZ-P_help-pHluorin, a strain that constitutively expresses the pH-sensitive fluorescent protein pHluorin, as a sensor strain to detect disruption of the pH gradient by the membrane-damaging activity of bacteriocins. The ratiometric fluorescence properties of pHluorin were validated both in crude extracts and permeabilized cells of this sensor strain. L. monocytogenes EGD-e/pNZ-P_help-pHluorin was used to assess membrane damaging activity of the bacteriocins nisin A and pediocin PA-1 and to determine the minimal concentrations required for full disruption of the pH gradient across the membrane. Moreover, the sensor strain proved useful to analyze the presence of compounds affecting membrane integrity in supernatants of a nisin Z-producing Lactococcus lactis strain at different timepoints during growth. Supernatants of this strain that were active in disrupting the pH gradient across the membrane were also shown to inhibit growth of L. monocytogenes. In summary, the presented results suggest that the generated sensor strain is a convenient, fast and reliable tool to identify and characterize novel bacteriocins and other compounds that target membrane integrity.

Carbohydrate Transport by Group Translocation: The Bacterial Phosphoenolpyruvate: Sugar Phosphotransferase System

The Bacterial Phosphoenolpyruvate (PEP) : Sugar Phosphotransferase System (PTS) mediates the uptake and phosphorylation of carbohydrates, and controls the carbon- and nitrogen metabolism in response to the availability of sugars. PTS occur in eubacteria and in a few archaebacteria but not in animals and plants. All PTS comprise two cytoplasmic phosphotransferase proteins (EI and HPr) and a species-dependent, variable number of sugar-specific enzyme II complexes (IIA, IIB, IIC, IID). EI and HPr transfer phosphorylgroups from PEP to the IIA units. Cytoplasmic IIA and IIB units sequentially transfer phosphates to the sugar, which is transported by the IIC and IICIID integral membrane protein complexes. Phosphorylation by IIB and translocation by IIC(IID) are tightly coupled. The IIC(IID) sugar transporters of the PTS are in the focus of this review. There are four structurally different PTS transporter superfamilies (glucose, glucitol, ascorbate, mannose) . Crystal structures are available for transporters of two superfamilies: bcIIC^mal (MalT, 5IWS, 6BVG) and bcIIC^chb (ChbC, 3QNQ) of B. subtilis from the glucose family, and IIC^asc (UlaA, 4RP9, 5ZOV) of E. coli from the ascorbate superfamily . They are homodimers and each protomer has an independent transport pathway which functions by an elevator-type alternating-access mechanism. bcIIC^mal and bcIIC^chb have the same fold, IIC^asc has a completely different fold. Biochemical and biophysical data accumulated in the past with the transporters for mannitol (IICBA^mtl) and glucose (IICB^glc) are reviewed and discussed in the context of the bcIIC^mal crystal structures. The transporters of the mannose superfamily are dimers of protomers consisting of a IIC and a IID protein chain. The crystal structure is not known and the topology difficult to predict. Biochemical data indicate that the IICIID complex employs a different transport mechanism . Species specific IICIID serve as a gateway for the penetration of bacteriophage lambda DNA across, and insertion of class IIa bacteriocins into the inner membrane. PTS transporters are inserted into the membrane by SecYEG translocon and have specific lipid requirements. Immunoelectron- and fluorescence microscopy indicate a non-random distribution and supramolecular complexes of PTS proteins.