Synthesis, antimicrobial activity and conformational analysis of the class IIa bacteriocin pediocin PA-1 and analogs thereof

Genome mining of Lactiplantibacillus plantarum PA21: insights into its antimicrobial potential

BACKGROUND

The dramatic increase of antimicrobial resistance in the healthcare realm has become inexorably linked to the abuse of antibiotics over the years. Therefore, this study seeks to identify potential postbiotic metabolites derived from lactic acid bacteria such as Lactiplantibacillus plantarum that could exhibit antimicrobial properties against multi-drug resistant pathogens.

RESULTS

In the present work, the genome sequence of Lactiplantibacillus plantarum PA21 consisting of three contigs was assembled to a size of 3,218,706 bp. Phylogenomic analysis and average nucleotide identity (ANI) revealed L. plantarum PA21 is closely related to genomes isolated from diverse niches such as dairy products, food, and animals. Genome mining through the BAGEL4 and antiSMASH database revealed four bacteriocins in a single cluster and four regions of biosynthetic gene clusters responsible for the production of bioactive compounds. The potential probiotic genes indirectly responsible for postbiotic metabolites production were also identified. Additionally, in vitro studies showed that the L. plantarum PA21 cell-free supernatant exhibited antimicrobial activity against all nine methicillin-resistant Staphylococcus aureus (MRSA) and three out of 13 Klebsiella pneumoniae clinical isolates tested.

CONCLUSION

Results in this study demonstrates that L. plantarum PA21 postbiotic metabolites is a prolific source of antimicrobials against multi-drug resistant pathogens with potential antimicrobial properties.

Heterologous expression of pediocin PA-1 in Pichia pastoris: cloning, expression, characterization, and application in pork bologna preservation

OBJECTIVE

Pediocin PA-1, an antimicrobial peptide derived from Pediococcus acidilactici PAC1.0, has a potential application as a food preservative thanks to its strong inhibitory activity against the foodborne pathogen L. monocytogenes. This study aimed to produce Pediocin PA-1 from the yeast P. pastoris and evaluate its characteristics.

METHODS

Gene encoding Pediocin PA-1 was integrated into P. pastoris X33 genome to establish the strain X33::ped, which could produce and secrete this peptide into culture medium. The antimicrobial activity of Pediocin PA-1 was examined using agar diffusion assay. The stability of pediocin PA-1 was determined based on its remaining antibacterial activity after exposure to proteases and extreme pH and temperatures. The potential use of this bacteriocin in food preservation was demonstrated using the L. monocytogenes infected pork bologna. The anticancer activity of Pediocin PA-1 was also investigated on some cancer cells using MTT assay.

RESULTS

We established the yeast P. pastoris X33::ped capable of producing pediocin PA-1 with antimicrobial activity against L. monocytogenes and some other harmful bacteria. Pediocin PA-1 was stable at 100˚C and resistant against pH 1-12 for 1 h, but susceptible to trypsin, α-chymotrypsin, and proteinase K. This peptide could reduce the number of L. monocytogenes in pork bologna by 3.59 log CFU/g after 7 days of storage at 4˚C. Finally, Pediocin PA-1 (25 µg/ml) inhibited the proliferation of A549 and Hela cancer cells.

CONCLUSION

We succeeded in producing active Pediocin PA-1 from P. pastoris and demonstrated its potential use in food preservation and pharmaceutical industry.

The Progress of the Biotechnological Production of Class IIa Bacteriocins in Various Cell Factories and Its Future Challenges

Class IIa bacteriocins produced in lactic acid bacteria are short cationic peptides with antimicrobial activity. In the search for new biopreservation agents, class IIa bacteriocins are considered to be the best potential candidates, not only due to their large abundance but also because of their high biological activity and excellent thermal stability. However, regulated by the biosynthetic regulatory system, the natural class IIa bacteriocin yield is low, and the extraction process is complicated. The biotechnological production of class IIa bacteriocins in various cell factories has been attempted to improve this situation. In this review, we focus on the application of biotechnological routes for class IIa bacteriocin production. The drawbacks and improvements in the production of class IIa bacteriocins in various cell factories are discussed. Furthermore, we present the main challenge of class IIa bacteriocins, focusing on increasing their production by constructing suitable cell factories. Recombinant bacteriocins have made considerable progress from inclusion body formation, dissolved form and low antibacterial activity to yield recovery. The development of prospective cell factories for the biotechnological production of bacteriocins is still required, which may facilitate the application of bacteriocins in the food industry.

Influence of different culture media on the antimicrobial activity of Pediococcus pentosaceus ST65ACC against Listeria monocytogenes

Pediococcus pentosaceus ST65ACC is a bacteriocinogenic lactic acid bacteria (LAB) isolated from Brazilian artisanal cheese that is capable of inhibiting different food pathogens, mainly Listeria monocytogenes. The production of bacteriocins can be influenced by several growth conditions, such as temperature, pH, and medium composition. This study aimed to evaluate the effect of different culture media on the production of bacteriocins and antimicrobial activity of P. pentosaceus ST65ACC on L. monocytogenes Scott A. The strains were inoculated alone and in coculture in four different media: BHI broth, MRS broth, meat broth, and reconstituted skim milk (RSM) 10% (w/v). The culture media were then incubated at 37 °C for 96 h, and count analysis, pH measurement, and bacteriocin production were performed at 0, 24, 48, 72 and 96 h. L. monocytogenes was inhibited to nondetectable levels in coculture with P. pentosaceus ST65ACC in MRS broth within 96 h, consistent with the high production of bacteriocin throughout the analysis period (3,200-12,800 AU/mL). However, lower inhibitory activities of P. pentosaceus ST65ACC on L. monocytogenes Scott A were recorded in BHI, RSM, and meat broth, with low or no production of bacteriocins at the analyzed times. The composition of these culture media may have repressed the production and activity of bacteriocins and, consequently, the antagonist activity of P. pentosaceus ST65ACC on L. monocytogenes Scott A. The results showed that the antimicrobial activity was more effective in MRS broth, presenting greater production of bacteriocins and less variability when compared to the other media analyzed.

Insights into Molecular Interactions between a GAPDH-Related Fish Antimicrobial Peptide, Analogs Thereof, and Bacterial Membranes

Interactions between SJGAP (skipjack tuna GAPDH-related antimicrobial peptide) and four analogs thereof with model bacterial membranes were studied using Fourier-transform infrared spectroscopy (FTIR) and molecular dynamics (MD) simulations. MD trajectory analyses showed that the N-terminal segment of the peptide analogs has many contacts with the polar heads of membrane phospholipids, while the central α helix interacts strongly with the hydrophobic core of the membranes. The peptides also had a marked influence on the wave numbers associated with the phase transition of phospholipids organized as liposomes in both the interface and aliphatic chain regions of the infrared spectra, supporting the interactions observed in the MD trajectories. In addition, interesting links were found between peptide interactions with the aliphatic chains of membrane phospholipids, as determined by FTIR and from the MD trajectories, and the membrane permeabilization capacity of these peptide analogs, as previously demonstrated. To summarize, the combined experimental and computational efforts have provided insights into crucial aspects of the interactions between the investigated peptides and bacterial membranes. This work thus makes an original contribution to our understanding of the molecular interactions underlying the antimicrobial activity of these GAPDH-related antimicrobial peptides from Scombridae.

Bacteriocins: potentials and prospects in health and agrifood systems

Bacteriocins are highly diverse, abundant, and heterogeneous antimicrobial peptides that are ribosomally synthesized by bacteria and archaea. Since their discovery about a century ago, there has been a growing interest in bacteriocin research and applications. This is mainly due to their high antimicrobial properties, narrow or broad spectrum of activity, specificity, low cytotoxicity, and stability. Though initially used to improve food quality and safety, bacteriocins are now globally exploited for innovative applications in human, animal, and food systems as sustainable alternatives to antibiotics. Bacteriocins have the potential to beneficially modulate microbiota, providing viable microbiome-based solutions for the treatment, management, and non-invasive bio-diagnosis of infectious and non-infectious diseases. The use of bacteriocins holds great promise in the modulation of food microbiomes, antimicrobial food packaging, bio-sanitizers and antibiofilm, pre/post-harvest biocontrol, functional food, growth promotion, and sustainable aquaculture. This can undoubtedly improve food security, safety, and quality globally. This review highlights the current trends in bacteriocin research, especially the increasing research outputs and funding, which we believe may proportionate the soaring global interest in bacteriocins. The use of cutting-edge technologies, such as bioengineering, can further enhance the exploitation of bacteriocins for innovative applications in human, animal, and food systems.

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.

Optimized recombinant production of the bacteriocin garvicin Q by Corynebacterium glutamicum

Bacteriocins are antimicrobial peptides applied in food preservation and are interesting candidates as alternatives to conventional antibiotics or as microbiome modulators. Recently, we established Corynebacterium glutamicum as a suitable production host for various bacteriocins including garvicin Q (GarQ). Here, we establish secretion of GarQ by C. glutamicum via the Sec translocon achieving GarQ titers of about 7 mg L-1 in initial fermentations. At neutral pH, the cationic peptide is efficiently adsorbed to the negatively charged envelope of producer bacteria limiting availability of the bacteriocin in culture supernatants. A combination of CaCl2 and Tween 80 efficiently reduces GarQ adsorption to C. glutamicum. Moreover, cultivation in minimal medium supplemented with CaCl2 and Tween 80 improves GarQ production by C. glutamicum to about 15 mg L-1 but Tween 80 resulted in reduced GarQ activity at later timepoints. Using a reporter strain and proteomic analyses, we identified HtrA, a protease associated with secretion stress, as another potential factor limiting GarQ production. Transferring production to HtrA-deficient C. glutamicum K9 improves GarQ titers to close to 40 mg L-1. Applying conditions of low aeration prevented loss in activity at later timepoints and improved GarQ titers to about 100 mg L-1. This is about 50-fold higher than previously shown with a C. glutamicum strain employing the native GarQ transporter GarCD for secretion and in the range of levels observed with the native producer Lactococcus petauri B1726. Additionally, we tested several synthetic variants of GarQ and were able to show that exchange of the methionine in position 5 to a phenylalanine (GarQM5F) results in markedly increased activity against Lactococcus lactis and Listeria monocytogenes. In summary, our findings shed light on several aspects of recombinant GarQ production that may also be of relevance for production with natural producers and other bacteriocins.

Effect of Disulfide Bonds on the Thermal Stability of Pediocin: In-silico Screening Using Molecular Dynamics Simulation

The thermal stability properties of pediocin at 310, 313, 323, 333, 343, and 348 K (37, 40, 50, 60, 70, and 75°C, respectively) are reported in this study. A theoretical approach, such as the molecular dynamics method, was used to analyze the structure. Molecular dynamics simulation confirms the stability of molecules with Cys. Furthermore, this study reveals that Cys residues play an essential role in structure stability at high temperatures. To understand the structural basis for the stability of pediocin, a detailed in-silico analysis using molecular dynamics simulations to explore the thermal stability profiles of the compounds was conducted. This study shows that thermal effects fundamentally alter the functionally crucial secondary structure of pediocin. However, as previously reported, pediocin's activity was strictly conserved due to the disulfide bond between Cys residues. These findings reveal, for the first time, the dominant factor behind the thermodynamic stability of pediocin.

Comparative genomics reveals key molecular targets for mutant Pediococcus pentosaceus C23221 producing pediocin

Listeria monocytogenes is a common microorganism that causes food spoilage. Pediocins are some biologically active peptides or proteins encoded by ribosomes, which have a strong antimicrobial activity against L. monocytogenes. In this study, the antimicrobial activity of previously isolated P. pentosaceus C-2-1 was enhanced by ultraviolet (UV) mutagenesis. A positive mutant strain P. pentosaceus C23221 was obtained after 8 rounds of UV irradiation with increased antimicrobial activity of 1448 IU/mL, which was 8.47 folds higher than that of wild-type C-2-1. The genome of strain C23221 and wild-type C-2-1 was compared with identify the key genes for higher activity. The genome of the mutant strain C23221 consists of a chromosome of 1,742,268 bp, with 2052 protein-coding genes, 4 rRNA operons, and 47 tRNA genes, which is 79,769 bp less than the original strain. Compared with strain C-2-1, a total of 19 deduced proteins involved in 47 genes are unique to C23221 analyzed by GO database; the specific ped gene related to bacteriocin biosynthesis were detected using antiSMASH in mutant C23221, indicating mutant C23221 produced a new bacteriocin under mutagenesis conditions. This study provides genetic basis for further constituting a rational strategy to genetically engineer wild-type C-2-1 into an overproducer.

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.

In Silico Analysis of Bacteriocins from Lactic Acid Bacteria Against SARS-CoV-2

The COVID-19 pandemic caused by a novel coronavirus (SARS-CoV-2) is a serious health concern in the twenty-first century for scientists, health workers, and all humans. The absence of specific biotherapeutics requires new strategies to prevent the spread and prophylaxis of the novel virus and its variants. The SARS-CoV-2 virus shows pathogenesis by entering the host cells via spike protein and Angiotensin-Converting Enzyme 2 receptor protein. Thus, the present study aims to compute the binding energies between a wide range of bacteriocins with receptor-binding domain (RBD) on spike proteins of wild type (WT) and beta variant (lineage B.1.351). Molecular docking analyses were performed to evaluate binding energies. Upon achieving the best bio-peptides with the highest docking scores, further molecular dynamics (MD) simulations were performed to validate the structure and interaction stability. Protein-protein docking of the chosen 22 biopeptides with WT-RBD showed docking scores lower than -7.9 kcal/mol. Pediocin PA-1 and salivaricin P showed the lowest (best) docking scores of - 12 kcal/mol. Pediocin PA-1, salivaricin B, and salivaricin P showed a remarkable increase in the double mutant's predicted binding affinity with -13.8 kcal/mol, -13.0 kcal/mol, and -12.5 kcal/mol, respectively. Also, a better predicted binding affinity of pediocin PA-1 and salivaricin B against triple mutant was observed compared to the WT. Thus, pediocin PA-1 binds stronger to mutants of the RBD, particularly to double and triple mutants. Salivaricin B showed a better predicted binding affinity towards triple mutant compared to WT, showing that it might be another bacteriocin with potential activity against the SARS-CoV-2 beta variant. Overall, pediocin PA-1, salivaricin P, and salivaricin B are the most promising candidates for inhibiting SARS-CoV-2 (including lineage B.1.351) entrance into the human cells. These bacteriocins derived from lactic acid bacteria hold promising potential for paving an alternative way for treatment and prophylaxis of WT and beta variants.

Demystifying Bacteriocins of Human Microbiota by Genome Guided Prospects: An Impetus to Rekindle the Antimicrobial Research

The human microbiome is a reservoir of potential bacteriocins that can counteract multidrug resistant bacterial pathogens. Unlike antibiotics, bacteriocins selectively inhibit a spectrum of competent bacteria and are said to safeguard gut commensals, reducing the chance of dysbiosis. Bacteriocinogenic probiotics or bacteriocins of human origin will be more pertinent in human physiological conditions for therapeutic applications to act against invading pathogens. Recent advancement in the omics approach enables the mining of diverse and novel bacteriocins by identifying biosynthetic gene clusters from the human microbial genome, pangenome or shotgun metagenome, which is a breakthrough in the discovery line of novel bacteriocins. This review summarizes the most recent trends and therapeutic potential of bacteriocins of human microbial origin, the advancement in the in silico algorithms and databases in the discovery of novel bacteriocin, and how to bridge the gap between the discovery of bacteriocin genes from big datasets and their in vitro production. Besides, the later part of the review discussed the various impediments in their clinical applications and possible solution to bring them into the frontline therapeutics to control infections, thereby meeting the challenges of global antimicrobial resistance.

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.

Pan-genomic and comparative analysis of Pediococcus pentosaceus focused on the in silico assessment of pediocin-like bacteriocins

Bacteriocins are antimicrobial peptides produced by different species of bacteria, especially the Gram-positive lactic acid bacteria (LAB). Pediococcus pentosaceus is widely applied in the industry and stands out as Bacteriocin-Like Inhibitory Substances (BLIS) producer known to inhibit pathogens commonly considered a concern in the food industries. This study aimed to perform in silico comparisons of P. pentosaceus genomes available in the public GenBank database focusing on their pediocin-like bacteriocins repertoire. The pan-genome analysis evidenced a temporal signal in the pattern of gene gain and loss, supporting the hypothesis that the complete genetic repertoire of this group of bacteria is still uncovered. Thirteen bacteriocin genes from Class II and III were predicted in the accessory genome. Four pediocin-like bacteriocins (54% of the detected bacteriocin repertoire) and their accompanying immunity genes are highlighted; penocin A, coagulin A, pediocin PA-1, and plantaricin 423. Additionally, in silico, modeling of the pediocin-like bacteriocins revealed different configurations of the helix motif compared to other physically determined pediocin-like structures. Comparative and phylogenomic analyses support the hypothesis that a dynamic mechanism of bacteriocin acquisition and purging is not dependent on the bacterial isolation source origin. Synteny analysis revealed that while coagulin A, pediocin PA-1, and Plantaricin 423 loci are associated with insertion sequences mainly from the IS30 family and are likely of plasmid origin, penocin A lies in a conserved chromosomal locus. The results presented here provide insights into the unique pediocin-like bacteriocin peptide fold, genomic diversity, and the evolution of the bacteriocin genetic repertoire of P. pentosaceus, shedding new insights into the role of these biomolecules for application in inhibiting bacterial pathogens, and suggesting that prospecting and sequencing new strains is still an alternative to mining for new probiotic compounds.

Advances in Rational Protein Engineering toward Functional Architectures and Their Applications in Food Science

Protein biomolecules including enzymes, cagelike proteins, and specific peptides have been continuously exploited as functional biomaterials applied in catalysis, nutrient delivery, and food preservation in food-related areas. However, natural proteins usually function well in physiological conditions, not industrial conditions, or may possess undesirable physical and chemical properties. Currently, rational protein design as a valuable technology has attracted extensive attention for the rational engineering or fabrication of ideal protein biomaterials with novel properties and functionality. This article starts with the underlying knowledge of protein folding and assembly and is followed by the introduction of the principles and strategies for rational protein design. Basic strategies for rational protein engineering involving experienced protein tailoring, computational prediction, computation redesign, and de novo protein design are summarized. Then, we focus on the recent progress of rational protein engineering or design in the application of food science, and a comprehensive summary ranging from enzyme manufacturing to cagelike protein nanocarriers engineering and antimicrobial peptides preparation is given. Overall, this review highlights the importance of rational protein engineering in food biomaterial preparation which could be beneficial for food science.

In vitro assessment of skin sensitization, irritability and toxicity of bacteriocins and reuterin for possible topical applications

Bacteriocins and reuterin are promising antimicrobials for application in food, veterinary, and medical sectors. In the light of their high potential for application in hand sanitizer, we investigated the skin toxicity of reuterin, microcin J25, pediocin PA-1, bactofencin A, and nisin Z in vitro using neutral red and LDH release assays on NHEK cells. We determined their skin sensitization potential using the human cell line activation test (h-CLAT). Their skin irritation potential was measured on human epidermal model EpiDerm™. We showed that the viability and membrane integrity of NHEK cells remained unaltered after exposure to bacteriocins and reuterin at concentrations up to 400 µg/mL and 80 mg/mL, respectively. Furthermore, microcin J25 and reuterin showed no skin sensitization at concentrations up to 100 µg/mL and 40 mg/mL, respectively, while pediocin PA-1, bactofencin A, and nisin Z caused sensitization at concentrations higher than 100 µg/mL. Tissue viability was unaffected in presence of bacteriocins and reuterin at concentrations up to 200 µg/mL and 40 mg/mL, respectively, which was confirmed by measuring cytokine IL-1α and IL-8 levels and by histological analysis. In conclusion, the current study provides scientific evidence that some bacteriocins and reuterin, could be safely applied topically as sanitizers at recommended concentrations.

Bacteriocin-Based Synergetic Consortia: a Promising Strategy to Enhance Antimicrobial Activity and Broaden the Spectrum of Inhibition

Bacteria-derived natural antimicrobial compounds such as bacteriocins, reruterin, and organic acids have recently received substantial attention as food preservatives or therapeutic alternatives in human or animal sectors. This study aimed to evaluate the antimicrobial activity of different bacteria-derived antimicrobials, alone or in combination, against a large panel of Gram-negative and Gram-positive bacteria. Bacteriocins, including microcin J25, pediocin PA-1, nisin Z, and reuterin, were investigated alone or in combination with lactic acid and citric acid, using a checkerboard assay. Concentrations were selected based on predetermined MICs against Salmonella enterica subsp. enterica serovar Newport ATCC 6962 and Listeria ivanovii HPB28 as Gram-negative and Gram-positive indicator strains, respectively. The results demonstrated that the combination of microcin J25 + citric acid + lactic acid; microcin J25 + reuterin + citric acid; and microcin J25 + reuterin + lactic acid tested against S. Newport ATCC 6962 showed synergistic effects (FIC index = 0.5). Moreover, a combination of pediocin PA-1 + citric acid + lactic acid; and reuterin + citric acid + lactic acid against L. ivanovii HPB28 showed a partially synergistic interactions (FIC index = 0.75). Nisin Z exerted a partially synergistic effect in combination with acids (FIC index = 0.625 -0.75), whereas when it was combined with reuterin or pediocin PA-1, it showed additive effects (FIC index = 1) against L. ivanovii HPB28. The inhibitory activity of synergetic consortia were tested against a large panel of Gram-positive and Gram-negative bacteria. According to our results, combining different antimicrobials with different mechanisms of action led to higher potency and a broad spectrum of inhibition, including multidrug-resistance pathogens.

IMPORTANCE Reuterin and bacteriocins, including microcin J25, pediocin PA-1, nisin were produced and purified with >90% purity. Using the broth-based checkerboard assay the interaction between these compounds (synergetic, additive, or antagonistic) was assessed. By combining different natural antimicrobials with different modes of action and structure (reuteirn, microcin J25, pediocin PA-1, and organic acids), we successfully developed five different synergetic consortia with improved antimicrobial activity and a broad spectrum of inhibition. These consortia were shown to be effective against a large panel of pathogenic and spoilage microorganisms as well as clinically important multidrug-resistance bacteria. Moreover, because the lower concentrations of bacteriocins and reuterin are used in the synergetic consortia, there is a limited risk of toxicity and resistance development for these compounds.

Structure and properties of antimicrobial peptides produced by antagonist microorganisms isolated from Siberian natural objects

Introduction. Public healthcare urgently needs new pharmaceuticals – alternative to traditional antibiotics – that pathogens develop no resistance to. Of special interest in this regard are antimicrobial, ribosomally synthesized bacterial peptides or bacteriocins. In this work, we aimed to study the structure and properties of antimicrobial peptides produced by antagonist microorganisms isolated from the natural objects of the Siberian region. Study objects and methods. The study objects were bacteria isolated from the natural sources of Kuzbass. After culturing bacteria, total protein was precipitated from the culture fluid and separated into fractions by gel permeation HPLC. Their amino acid sequences were determined by MALDI-TOF mass spectrometry. The antibacterial (against Bacillus pumilus and Escherichia coli) and fungicidal (against Aspergillus flavus and Aspergillus niger) properties of the peptides were studied by the disk diffusion method. Results and discussion. Seven peptides with different amino acid sequences were isolated from the culture fluid of bacteria, five of which had no analogues in the PepBank and Uniprot data banks. The peptide with an amino acid sequence of VMCLARKCSQGLIVKAPLM (2061.66 Da) was homologous to the cysteine membrane protein Giardia lamblia P15, and the peptide with an amino acid sequence of AVPSMKLCIQWSPVRASPCVMLGI (2587.21 Da) showed a homology with the Planctomycetes bacterium I41 peptides. We found antibacterial (against gram-positive and gram-negative bacteria) and fungicidal (against Aspergillus) properties in the peptide fractions. Conclusion. Antimicrobial peptides produced by bacteria isolated from the natural objects of the Siberian region can be used to create pharmaceuticals as an alternative to traditional antibiotics to treat infectious diseases.

Gastrointestinal Stability and Cytotoxicity of Bacteriocins From Gram-Positive and Gram-Negative Bacteria: A Comparative in vitro Study

Bacteriocins are receiving increased attention as potent candidates in food preservation and medicine. Although the inhibitory activity of bacteriocins has been studied widely, little is known about their gastrointestinal stability and toxicity toward normal human cell lines. The aim of this study was to evaluate the gastrointestinal stability and activity of microcin J25, pediocin PA-1, bactofencin A and nisin using in vitro models. In addition cytotoxicity and hemolytic activity of these bacteriocins were investigated on human epithelial colorectal adenocarcinoma cells (Caco-2) and rat erythrocytes, respectively. Pediocin PA-1, bactofencin A, and nisin were observed to lose their stability while passing through the gastrointestinal tract, while microcin J25 is only partially degraded. Besides, selected bacteriocins were not toxic to Caco-2 cells, and integrity of cell membrane was observed to remain unaffected in presence of these bacteriocins at concentrations up to 400 μg/mL. In hemolysis study, pediocin PA-1, bactofencin A, and nisin were observed to lyse rat erythrocytes at concentrations higher than 50 μg/mL, while microcin J25 showed no effect on these cells. According to data indicating gastrointestinal degradation and the absence of toxicity of pediocin PA-1, bactofencin A, and microcin J25 they could potentially be used in food or clinical applications.

Genomic Analyses of Pediococcus pentosaceus ST65ACC, a Bacteriocinogenic Strain Isolated from Artisanal Raw-Milk Cheese

Pediococcus pentosaceus ST65ACC was obtained from a Brazilian artisanal cheese (BAC) and characterized as bacteriocinogenic. This strain presented beneficial properties in previous studies, indicating its potential as a probiotic candidate. In this study, we aimed to carry out a genetic characterization based on whole-genome sequencing (WGS), including taxonomy, biotechnological properties, bacteriocin clusters and safety-related genes. WGS was performed using the Illumina MiSeq platform and the genome was annotated with the Prokaryotic Genome Annotation (Prokka). P. pentosaceus ST65ACC taxonomy was investigated and bacteriocin genes clusters were identified by BAGEL4, metabolic pathways were analyzed by Kyoto Encyclopedia of Genes and Genomes (KEGG) and safety-related genes were checked. P. pentosaceus ST65ACC had a total draft genome size of 1,933,194 bp with a GC content of 37.00%, and encoded 1950 protein coding sequences (CDSs), 6 rRNA, 55 tRNA, 1 tmRNA and no plasmids were detected. The analysis revealed absence of a CRISPR/Cas system, bacteriocin gene clusters for pediocin PA-1/AcH and penocin-A were identified. Genes related to beneficial properties, such as stress adaptation genes and adhesion genes, were identified. Furthermore, genes related to biogenic amines and virulence-related genes were not detected. Genes related to antibiotic resistance were identified, but not in prophage regions. Based on the obtained results, the beneficial potential of P. pentosaceus ST65ACC was confirmed, allowing its characterization as a potential probiotic candidate.

An oxidation resistant pediocin PA-1 derivative and penocin A display effective anti-Listeria activity in a model human gut environment

Pediocin PA-1 is a class IIa bacteriocin that is particularly effective against the foodborne pathogen Listeria monocytogenes. The loss of activity of PA-1 pediocin due to methionine oxidation is one of the challenges that limit the wider application of the bacteriocin. In this study, we heterologously expressed an oxidation resistant form of pediocin PA-1, i.e., pediocin M31L, and compared its activity to that of native pediocin PA-1 and to penocin A, a pediocin-like bacteriocin that displays a narrower antimicrobial spectrum. Minimal inhibitory concentration assays revealed that pediocin M31L was as effective as PA-1 and more effective than synthetic penocin A against Listeria with negligible activity against a range of obligate anaerobic commensal gut bacterial species. The anti-Listeria activity of these pediocins was also assessed in a simulated human distal colon model assay using the L. monocytogenes, spiked at 6.5 ±   0.13 Log CFU/mL, as a bioindicator. At 24 h, pediocin M31L and penocin A (2.6 μM) reduced Listeria counts to 3.5 ± 0.4 and 3.64 ± 0.62 Log CFU/mL, respectively, whereas Listeria counts were considerably higher, i.e. 7.75 ±   0.43 Log CFU/mL, in the non-bacteriocin-containing control. Ultimately, it was established that synthetic penocin A and the stable pediocin M31L derivative, heterologously produced, display effective anti-Listeria activity in a human gut environment.

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.

Thiol- and Disulfide-Containing Vancomycin Derivatives Against Bacterial Resistance and Biofilm Formation

Antibiotic-resistant and biofilm-associated infections constitute a rapidly growing issue. Use of the last-resort antibiotic vancomycin is under threat due to the increasing appearance of vancomycin-resistant bacteria as well as the formation of biofilms. Herein, we report a series of novel vancomycin derivatives carrying thiol- and disulfide-containing moieties. The new compounds exhibited enhanced antibacterial activity against a broad range of bacterial strains, including vancomycin-resistant microbes and Gram-negative bacteria. Moreover, all obtained derivatives demonstrated improved antibiofilm formation activity against VanB-resistant Enterococcus compared to vancomycin. This work establishes a promising strategy for combating drug-resistant bacterial infections or disrupting biofilm formation and advances the knowledge on the structural optimization of antibiotics with sulfur-containing modifications.

Susceptibility to Nisin, Bactofencin, Pediocin and Reuterin of Multidrug Resistant Staphylococcus aureus, Streptococcus dysgalactiae and Streptococcus uberis Causing Bovine Mastitis

Antibiotics are the most effective strategy to prevent and treat intramammary infections. However, their misuse has led to the dissemination of multidrug resistant bacteria (MDR) for both animals and humans. Efforts to develop new alternative strategies to control bacterial infections related to MDR are continuously on the rise. The objective of this study was to evaluate the antimicrobial activity of different bacteriocins and reuterin against MDR Staphylococcus and Streptococcus clinical isolates involved in bovine mastitis. A bacterial collection including S. aureus (n = 19), S. dysgalactiae (n = 17) and S. uberis (n = 19) was assembled for this study. Antibiotic resistance profiles were determined by the disk diffusion method. In addition, sensitivity to bacteriocins and reuterin was evaluated by determining minimum inhibitory concentrations (MIC). A total of 21 strains (37.5%) were MDR. MICs ranged from ≤1.0 μg/mL to ≥100 μg/mL for nisin and 2.0 to ≥250 μg/mL for bactofencin. Reuterin was active against all tested bacteria, and MICs vary between 70 and 560 μg/mL. Interestingly, 20 MDR strains were inhibited by bactofencin at a concentration of ≤250 μg/mL, while 14 were inhibited by nisin at an MIC of ≤100 μg/mL. Pediocin did not show an inhibitory effect.

The microbiome-shaping roles of bacteriocins

The microbiomes on human body surfaces affect health in multiple ways. They include not only commensal or mutualistic bacteria but also potentially pathogenic bacteria, which can enter sterile tissues to cause invasive infection. Many commensal bacteria produce small antibacterial molecules termed bacteriocins that have the capacity to eliminate specific colonizing pathogens; as such, bacteriocins have attracted increased attention as potential microbiome-editing tools. Metagenome-based and activity-based screening approaches have strongly expanded our knowledge of the abundance and diversity of bacteriocin biosynthetic gene clusters and the properties of a continuously growing list of bacteriocin classes. The dynamic acquisition, diversification or loss of bacteriocin genes can shape the fitness of a bacterial strain that is in competition with bacteriocin-susceptible bacteria. However, a bacteriocin can only provide a competitive advantage if its fitness benefit exceeds the metabolic cost of production, if it spares crucial mutualistic partner strains and if major competitors cannot develop resistance. In contrast to most currently available antibiotics, many bacteriocins have only narrow activity ranges and could be attractive agents for precision therapy and prevention of infections. A common scientific strategy involving multiple disciplines is needed to uncover the immense potential of microbiome-shaping bacteriocins.

Wildlife symbiotic bacteria are indicators of the health status of the host and its ecosystem

Lactic acid bacteria (LAB) are gut symbionts that can be used as a model to understand the host-microbiota crosstalk under unpredictable environmental conditions such as wildlife ecosystems. The aim of this study was to determine whether viable LAB can be informative of the health status of wild boar populations. We monitored the genotype and phenotype of LAB based on markers that included safety and phylogenetic origin, antibacterial activity and immunomodulatory properties. A LAB profile dominated by lactobacilli appears to stimulate protective immune responses and relates to strains widely used as probiotics, resulting in a potentially healthy wildlife population whereas microbiota overpopulated by enterococci was observed in a hostile environment. These enterococci were closely related to pathogenic strains that have developed mechanisms to evade innate immune system, posing a potential risk for the host health. Furthermore, our LAB isolates displayed antibacterial properties in a species-dependent manner. Nearly all of them were able to inhibit bacterial pathogens, raising the possibility of using them as a la carte antibiotic alternative in the unexplored field of wildlife disease mitigation. Our study highlights that microbiological characterization of LAB is a useful indicator of wildlife health status and the ecological origin from which they derive. Significance Statement The wildlife symbiotic microbiota is an important component to the greater for greater diversity and functionality of their bacterial populations, influencing the host health and adaptability to its ecosystem. Although many microbes are partly responsible for the development of multiple physiological processes, only certain bacterial groups such as lactic acid bacteria (LAB) have the capacity to overpopulate the gut, promoting health (or disease) when specific genetic and environmental conditions are present. LAB have been exploited in many ways due to their probiotic properties, in particular lactobacilli, however their relationship with wildlife gut-associated microbiota hosts remains to be elucidated. On the other hand, it is unclear whether LAB such as enterococci, which have been associated with detrimental health effects, could lead to disease. These important questions have not been properly addressed in the field of wildlife, and therefore, should be clearly attained.

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.

A Novel Bacteriocin From Lactobacillus Pentosus ZFM94 and Its Antibacterial Mode of Action

Bacteriocins are bioactive antimicrobial peptides synthesized in the ribosome of numerous bacteria and released extracellularly. Pentocin ZFM94 produced by Lactobacillus pentosus (L. pentosus) ZFM94, isolated from infant feces with strong antibacterial activity, was purified by ammonium sulfate precipitation, dextran gel chromatography, and reverse-phase high-performance liquid chromatography (RP-HPLC). The molecular mass of the purified bacteriocin was 3,547.74 Da determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Pentocin ZFM94 exhibited broad-spectrum antimicrobial activity against tested Gram-positive and Gram-negative bacteria, and the minimal inhibitory concentrations (MICs) of Micrococcus luteus (M. luteus) 10,209, Staphylococcus aureus (S. aureus) D48, and Escherichia coli (E. coli) DH5α were 1.75, 2.00, and 2.50 μm, respectively. Pentocin ZFM94 was heat-stable (30 min at 80°C) and showed inhibitory activity over a wide pH range (5.00–7.00). It could be degraded by trypsin and pepsin, but not by amylase, lysozyme, lipase, and ribonuclease A. Fluorescence leakage assay showed that pentocin ZFM94 induced disruption of the cell membrane and caused leakage of cellular content. Furthermore, lipid II was not an antibacterial target of pentocin ZFM94. This study laid the foundation for further development and utilization of L. pentosus ZFM94 and its bacteriocin.

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.

Lactic Acid Bacteria Diversity and Characterization of Probiotic Candidates in Fermented Meats

Probiotics are defined as live microorganisms which confer health benefits to the host when administered in adequate amounts. Many lactic acid bacteria (LAB) strains have been classified as probiotics and fermented foods are an excellent source of such LAB. In this study, novel probiotic candidates from two fermented meats (pancetta and prosciutto) were isolated and characterized. LAB populations present in pancetta and prosciutto were evaluated and Lactiplantibacillus plantarum was found to be the dominant species. The antagonistic ability of selected isolates against LAB and non-LAB strains was investigated, in particular, the ability to produce anti-microbial compounds including organic acids and bacteriocins. Probiotic characteristics including antibiotic susceptibility, hydrophobicity and autoaggregation capacity; and ability to withstand simulated gastric juice, bile salt, phenol and NaCl were assessed. Among the characterized strains, L. plantarum 41G isolated from prosciutto was identified as the most robust probiotic candidate compared. Results from this study demonstrate that artisanal fermented meat is a rich source of novel strains with probiotic potential.

Genome Mining for Antimicrobial Compounds in Wild Marine Animals-Associated Enterococci

New ecosystems are being actively mined for new bioactive compounds. Because of the large amount of unexplored biodiversity, bacteria from marine environments are especially promising. Further, host-associated microbes are of special interest because of their low toxicity and compatibility with host health. Here, we identified and characterized biosynthetic gene clusters encoding antimicrobial compounds in host-associated enterococci recovered from fecal samples of wild marine animals remote from human-affected ecosystems. Putative biosynthetic gene clusters in the genomes of 22 Enterococcus strains of marine origin were predicted using antiSMASH5 and Bagel4 bioinformatic software. At least one gene cluster encoding a putative bioactive compound precursor was identified in each genome. Collectively, 73 putative antimicrobial compounds were identified, including 61 bacteriocins (83.56%), 10 terpenes (13.70%), and 2 (2.74%) related to putative nonribosomal peptides (NRPs). Two of the species studied, Enterococcus avium and Enterococcus mundtti, are rare causes of human disease and were found to lack any known pathogenic determinants but yet possessed bacteriocin biosynthetic genes, suggesting possible additional utility as probiotics. Wild marine animal-associated enterococci from human-remote ecosystems provide a potentially rich source for new antimicrobial compounds of therapeutic and industrial value and potential probiotic application.

Bacteriocins from Lactic Acid Bacteria. A Powerful Alternative as Antimicrobials, Probiotics, and Immunomodulators in Veterinary Medicine

In the search for an alternative treatment to reduce antimicrobial resistance, bacteriocins shine a light on reducing this problem in public and animal health. Bacteriocins are peptides synthesized by bacteria that can inhibit the growth of other bacteria and fungi, parasites, and viruses. Lactic acid bacteria (LAB) are a group of bacteria that produce bacteriocins; their mechanism of action can replace antibiotics and prevent bacterial resistance. In veterinary medicine, LAB and bacteriocins have been used as antimicrobials and probiotics. However, another critical role of bacteriocins is their immunomodulatory effect. This review shows the advances in applying bacteriocins in animal production and veterinary medicine, highlighting their biological roles.

Antimicrobial peptides against colorectal cancer-a focused review

Despite recent advances in the treatment of colorectal cancer (CRC), low patient survival rate due to emergence of drug resistant cancer cells, metastasis and multiple deleterious side effects of chemotherapy, is a cause of public concern globally. To negate these clinical conundrums, search for effective and harmless novel molecular entities for the treatment of CRC is an urgent necessity. Since antimicrobial peptides (AMPs) are part of innate immunity of living beings, it is quite imperative to look for essential attributes of these peptides which may contribute to their effectiveness against carcinogenesis. Once identified, those characteristics can be suitably modified using several synthetic and computational techniques to further enhance their selectivity and pharmacokinetic profiles. Hence, this review analyses scientific reports describing the antiproliferative action of AMPs derived from several sources, particularly focusing on various colon cancer in vitro/in vivo investigations. On perusal of the literature, it appears that AMPs based therapeutics would definitely find special place in CRC therapy in future either alone or as an adjunct to chemotherapy provided some necessary alterations are made in their natural structures to make them more compatible with modern clinical practice. In this context, further in-depth research is warranted in adequate in vivo models.

Mining, heterologous expression, purification, antibactericidal mechanism, and application of bacteriocins: A review

Bacteriocins are generally considered as low-molecular-weight ribosomal peptides or proteins synthesized by G⁺ and G^- bacteria that inhibit or kill other related or unrelated microorganisms. However, low yield is an important factor restricting the application of bacteriocins. This paper reviews mining methods, heterologous expression in different systems, the purification technologies applied to bacteriocins, and identification methods, as well as the antibacterial mechanism and applications in three different food systems. Bioinformatics improves the efficiency of bacteriocins mining. Bacteriocins can be heterologously expressed in different expression systems (e.g., Escherichia coli, Lactobacillus, and yeast). Ammonium sulfate precipitation, dialysis membrane, pH-mediated cell adsorption/desorption, solvent extraction, macroporous resin column, and chromatography are always used as purification methods for bacteriocins. The bacteriocins are identified through electrophoresis and mass spectrum. Cell envelope (e.g., cell permeabilization and pore formation) and inhibition of gene expression are common antibacterial mechanisms of bacteriocins. Bacteriocins can be added to protect meat products (e.g., beef and sausages), dairy products (e.g., cheese, milk, and yogurt), and vegetables and fruits (e.g., salad, apple juice, and soybean sprouts). The future research directions are also prospected.

Application of yeast surface display system in expression of recombinant pediocin PA-1 in Saccharomyces cerevisiae

Pediocin PA-1 is a bacteriocin that shows strongly anti-microbial activity against some Gram-positive pathogens such as Listeria monocytogenes, Staphylococcus aureus, and Enterococcus faecalis. With the broad inhibitory spectrum as well as high-temperature stability, pediocin has a potential application in the food preservation and pharmaceutical industry. Pediocin has been studied to express in many heterologous expression systems such as Escherichia coli, Saccharomyces cerevisiae, and Pichia pastoris as a free peptide. Here we showed in this study a new strategy by using yeast surface display system to produce the anchored pediocin PA-1 on the cell surface of Saccharomyces cerevisiae, which could be used directly as a pediocin resource. We had successfully constructed a recombinant S. cerevisiae W303 strain that could express pediocin PA-1 on the cell surface. The pediocin-expressing yeast could inhibit the growth of Shigella boydii and Shigella flexneri, which have never been reported before for pediocin activity. Besides, the pediocin expression level of the recombinant S. cerevisiae strain was also evaluated in three different media: synthetic defined (SD), basic medium (BM), and fermentation medium (FM). BM medium was shown to give the highest production yield of the recombinant yeast (4.75 ± 0.75 g dry cell weight per 1 L of culture) with the ratio number of the pediocin-expressing cells of 93.46 ± 2.45%. Taken together, the results clearly showed that pediocin can be displayed on yeast cell surface as anchored protein. The application of yeast cell surface system enables a new door of pediocin application on either food or feed industries. Graphical abstract.

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.

Phenotypic comparison and DNA sequencing analysis of a wild-type and a pediocin-resistant mutant of Listeria ivanovii

Listeria ivanovii is one of the two pathogenic species within the genus Listeria, the other being Listeria monocytogenes. In this study, we generated a stable pediocin resistant mutant Liv-r1 of a L. ivanovii strain, compared phenotypic differences between the wild-type and the mutant, localised the pediocin-induced mutations in the chromosome, and analysed the mechanisms behind the bacteriocin resistance. In addition to pediocin resistance, Liv-r1 was also less sensitive to nisin. The growth of Liv-r1 was significantly reduced with glucose and mannose, but less with cellobiose. The cells of Liv-r1 adsorbed less pediocin than the wild-type cells. Consequently, with less pediocin on the cell surface, the mutant was also less leaky, as shown as the release of intracellular lactate dehydrogenase to the supernatant. The surface of the mutant cells was more hydrophobic than that of the wild-type. Whole genome sequencing revealed numerous changes in the Liv-r1 chromosome. The mutations were found e.g., in genes encoding sigma-54-dependent transcription regulator and internalin B, as well as in genes involved in metabolism of carbohydrates such as glucose and cellobiose. Genetic differences observed in the mutant may be responsible for resistance to pediocin but no direct evidence is provided.

Nisin as a Novel Feed Additive: The Effects on Gut Microbial Modulation and Activity, Histological Parameters, and Growth Performance of Broiler Chickens

Two independent experiments were performed to evaluate the effect of nisin alone or with monensin on gut microbiota, gut microbial activities, and histomorphology (exp 1) and the effect of nisin application in a dose‒response manner on the growth performance of broiler chickens (exp 2). A total of 900 one-day-old female Ross 308 chicks (400, exp 1; 500, exp 2) were randomly distributed to four groups (exp 1; 10 replicate pens per treatment with 10 birds each), i.e., NA, no additives; MON, monensin (100 ppm); NIS, nisin (2700 IU/kg diet); and MON + NIS, a mixture of monensin (100 ppm) and nisin (2700 IU/kg diet); or 5 treatments (exp 2), NA, no additives; NIS100, nisin (100 IU/kg diet); NIS200, nisin (200 IU/kg diet); NIS400, nisin (400 IU/kg diet); and NIS800, nisin (800 IU/kg diet). Nisin supplementation positively affected the microbiota of the gut by reducing potentially pathogenic bacterial populations in the jejunum and ceca. The bacterial fermentation in the jejunum was significantly lowered by nisin addition. The addition of nisin from 100 IU to 800 IU decreased the FCR value over the entire experimental period. According to the results, nisin can be considered a natural dietary supplement for broiler chickens.

Heterologous Expression of the Class IIa Bacteriocins, Plantaricin 423 and Mundticin ST4SA, in Escherichia coli Using Green Fluorescent Protein as a Fusion Partner

The antilisterial class IIa bacteriocins, plantaricin 423 and mundticin ST4SA, have previously been purified from the cell-free supernatants of Lactobacillus plantarum 423 and Enterococcus mundtii ST4SA, respectively. Here, we present the fusions of mature plantaricin 423 and mundticin ST4SA to His-tagged green fluorescent protein (GFP) for respective heterologous expression in Escherichia coli. Fusion of plantaricin 423 and mundticin ST4SA to His-tagged GFP produced the fusion proteins GFP-PlaX and GFP-MunX, respectively. Both fusion proteins were autofluorescent, circumvented inclusion body formation and lowered the toxicity of class IIa bacteriocins during heterologous expression. Not only did GFP-class IIa fusion stabilize heterologous expression and boost yields, the fluorescent intensity of GFP-PlaX and GFP-MunX could be monitored quantitatively and qualitatively throughout expression and purification. This robust fluorometric property allowed rapid optimization of conditions for expression and bacteriocin liberation from GFP via the incorporated WELQut protease cleavage sequence. Incubation temperature and IPTG concentration had a significant effect on bacteriocin yield, and was optimal at 18°C and 0.1-0.2 mM, respectively. GFP-MunX was approximately produced at a yield of 153.30 mg/L culture which resulted in 12.4 mg/L active mundticin ST4SA after liberation and HPLC purification. While GFP-PlaX was produced at a yield of 121.29 mg/L culture, evidence suggests heterologous expression resulted in conformation isomers of WELQut liberated plantaricin 423.

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.

The case for class II bacteriocins: A biophysical approach using "suicide probes" in receptor-free hosts to study their mechanism of action

Class II bacteriocins are unmodified membrane-active peptides that act over a narrow spectrum of target bacteria. They bind a specific receptor protein on the membrane to form a pore, leading to membrane permeabilization and cell death. However, little is known about the molecular events triggering the pore formation after the bacteriocin recognizes the receptor. It is not clear yet if the pore is the same receptor forced into an open conformation or if the pore results from the bacteriocin insertion and oligomeric assembly in the lipid bilayer. In order to reveal which model is more suitable to explain the toxicity mechanism, in this work we use chimeric peptides, resulting from the fusion of the bitopic membrane protein EtpM with different class II bacteriocins: enterocin CRL35, pediocin PA-1 and microcin V. E. coli strains lacking the specific receptors for these bacteriocins were chosen as expression hosts. As these constructs display a lethal effect when they are heterologously expressed, they are called "suicide probes". The results suggest that, indeed, the specific receptor would act as a docking molecule more than as a structural piece of the pore, as long as the bacteriocin is somehow anchored to the membrane. These set of chimeric peptides also represent an in vivo system that allows to study the interaction of the bacteriocins with real bacterial membranes, instead of model membranes. Hence, the effects of these suicide probes in membrane fluidity and transmembrane potential were also assessed, using fluorescence spectroscopy. The data show that the different suicide probes are able to increase phospholipid order and depolarize the membranes of receptor-free bacterial cells.