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Synbiotics are mixtures of prebiotics and probiotics that enhance the activity of probiotic bacteria when co-administered to provide greater benefits to the host. Traditionally, the synbiotics that have been discovered enhance gut probiotic strains and are nutritionally complex molecules that survive digestive breakdown until they reach the later stages of the intestinal tract. Here, we screened and identified sugars or sugar substitutes as synbiotics for the oral probiotic strains Streptococcus salivarius BLIS K12 and BLIS M18. Using a modified deferred antagonism assay, we found that 0.5% (w/v) galactose and 2.5% (w/v) raffinose were the best candidates for use as synbiotics with BLIS K12 and M18, as they trigger enhanced antimicrobial activity against a range of bacteria representing species from the mouth, gut, and skin. Using reverse transcriptase quantitative PCR, we found that this enhanced antimicrobial activity was caused by the upregulation of the lantibiotic genes salA, salB, and sal9 in either K12 or M18. This led to the conclusion that either 2.5% (w/v) raffinose or 0.5% (w/v) galactose, respectively, are suitable synbiotics for use in conjunction with BLIS K12 and M18 to enhance probiotic performance. [ABSTRACT FROM AUTHOR]

Synbiotics are mixtures of prebiotics and probiotics that enhance the activity of probiotic bacteria when co-administered to provide greater benefits to the host. Traditionally, the synbiotics that have been discovered enhance gut probiotic strains and are nutritionally complex molecules that survive digestive breakdown until they reach the later stages of the intestinal tract. Here, we screened and identified sugars or sugar substitutes as synbiotics for the oral probiotic strains Streptococcus salivarius BLIS K12 and BLIS M18. Using a modified deferred antagonism assay, we found that 0.5% (w/v) galactose and 2.5% (w/v) raffinose were the best candidates for use as synbiotics with BLIS K12 and M18, as they trigger enhanced antimicrobial activity against a range of bacteria representing species from the mouth, gut, and skin. Using reverse transcriptase quantitative PCR, we found that this enhanced antimicrobial activity was caused by the upregulation of the lantibiotic genes salA, salB, and sal9 in either K12 or M18. This led to the conclusion that either 2.5% (w/v) raffinose or 0.5% (w/v) galactose, respectively, are suitable synbiotics for use in conjunction with BLIS K12 and M18 to enhance probiotic performance.

Antimicrobial resistance presents a substantial threat to global public health, demanding urgent attention and action. This study focuses on lanthipeptides, ribosomally encoded peptides that display significant structural diversity and hold promising potential as antibiotics. Genome mining was employed to locate biosynthetic gene clusters (BGCs) containing class II lanthipeptide synthetases encoded by lanM genes. A phylogenetic study analyzing homologous sequences of functional LanM sequences revealed a unique evolutionary clade of 17 LanM proteins associated with 12 Clostridium bacterial genomes. In silico exploration identified nine complete BGCs, including one super-cluster containing two co-localized operons from Clostridium cellulovorans 743B, that encode for two new peptides named clostrisin and cellulosin. Each operon was heterologously expressed in Escherichia coli. Molecular weights associated with the expected post-translational modifications of the purified lanthipeptide were confirmed by MS–MS/MS analysis for cellulosin, while clostrisin was not post-translationally modified. Both peptides demonstrated antimicrobial activity against multidrug-resistant bacteria, such as a clinical strain of Staphylococcus epidermidis MIQ43 and Pseudomonas aeruginosa PA14. This is the first report of lanthipeptides from the Clostridium genus produced with its native biosynthetic machinery, as well as chemically and biologically characterized. This study showcases the immense potential of genome mining in identifying new RiPP synthetases and associated bioactive peptides.

Objective: Lantibiotics are a family of bacterial antimicrobial peptides synthesized by ribosomes, that undergo post-translational modification to form lanthionine (Lan) and methyllanthionine (MeLan) residues. Lantibiotics are currently considered promising agents for combating antibiotic-resistant bacterial infections. This paper presents a biotechnological method for obtaining two components of the lantibiotic lichenicidin from Bacillus licheniformis B-511, Lchα and Lchβ. Such a system has the potential to facilitate the production of not only lichenicidin, but also other lantibiotics, including two-component ones, and also to enable the study of their biosynthesis and the activity and substrate specificity of modifying enzymes. Methods: The developed system is based on heterologous coexpression of the genes of Lchα and Lchβ precursors with the genes of their corresponding modifying enzymes in the cytoplasm of Escherichia coli BL21(DE3). Subsequent steps included immobilized metal affinity chromatography of the His-tagged hybrid peptide under denaturing conditions, cyanogen bromide cleavage in acidic medium, and final purification using reverse-phase HPLC. Results and Discussion: The system was employed for the expression and purification of lantibiotics, resulting in the successful isolation of the β-component of lichenicidin in high yield (approximately 4 mg/L of culture). This purified beta component exhibited structural and functional characteristics comparable to its natural counterpart, which was purified from the natural producer. However, the yield of the mature α-component of lichenicidin in such a system was significantly lower. Conclusions: The work presents a biotechnological method for obtaining recombinant two-component lantibiotic lichenicidin, which has proven to be particularly effective in the case of Lchβ. The developed method can also be applied to the production of other promising lantibiotics and their further research. [ABSTRACT FROM AUTHOR]

Bacteriocins is the name given to products of the secondary metabolism of many bacterial genera that must display antimicrobial activity. Although there are several bacteriocins described today, it has not been possible to reach a consensus on the method of classification for these biomolecules. In addition, many of them are not yet authorized for therapeutic use against multi-drug-resistant microorganisms due to possible toxic effects. However, recent research has achieved considerable progress in the understanding, classification, and elucidation of their mechanisms of action against microorganisms, which are of medical and biotechnological interest. Therefore, in more current times, protocols are already being conducted for their optimal use, in the hopes of solving multiple health and food conservation problems. This review aims to synthetize the information available nowadays regarding bacteriocins, and their classification, while also providing an insight into the future possibilities of their usage for both the pharmaceutical, food, and biotechnological industry. [ABSTRACT FROM AUTHOR]

Abstract Increasing antimicrobial resistance in Enterococcus faecium necessitates the search for novel treatment agents, such as bacteriocins. In this study, we conducted an in vivo assessment of five bacteriocins, namely Lacticin Z, Lacticin Q, Garvicin KS (ABC), Aureocin A53 and Microbisporicin (NAI-107), against vanB-resistant Enterococcus faecium using a Galleria mellonella model. Our in vitro experiments demonstrated the efficacy of all five bacteriocins against vanB-resistant E. faecium with only NAI-107 demonstrating in vivo efficacy. Notably, NAI-107 exhibited efficacy across a range of tested doses, with the highest efficacy observed at a concentration of 16 µg/mL. Mortality rates in the group treated with 16 µg/mL NAI-107 were lower than those observed in the linezolid-treated group. These findings strongly suggest that NAI-107 holds promise as a potential alternative therapeutic agent for treating infections caused by resistant E. faecium and warrants further investigation.

Increasing antimicrobial resistance in Enterococcus faecium necessitates the search for novel treatment agents, such as bacteriocins. In this study, we conducted an in vivo assessment of five bacteriocins, namely Lacticin Z, Lacticin Q, Garvicin KS (ABC), Aureocin A53 and Microbisporicin (NAI-107), against vanB-resistant Enterococcus faecium using a Galleria mellonella model. Our in vitro experiments demonstrated the efficacy of all five bacteriocins against vanB-resistant E. faecium with only NAI-107 demonstrating in vivo efficacy. Notably, NAI-107 exhibited efficacy across a range of tested doses, with the highest efficacy observed at a concentration of 16 µg/mL. Mortality rates in the group treated with 16 µg/mL NAI-107 were lower than those observed in the linezolid-treated group. These findings strongly suggest that NAI-107 holds promise as a potential alternative therapeutic agent for treating infections caused by resistant E. faecium and warrants further investigation. [ABSTRACT FROM AUTHOR]

Bacteriocins is the name given to products of the secondary metabolism of many bacterial genera that must display antimicrobial activity. Although there are several bacteriocins described today, it has not been possible to reach a consensus on the method of classification for these biomolecules. In addition, many of them are not yet authorized for therapeutic use against multi-drug-resistant microorganisms due to possible toxic effects. However, recent research has achieved considerable progress in the understanding, classification, and elucidation of their mechanisms of action against microorganisms, which are of medical and biotechnological interest. Therefore, in more current times, protocols are already being conducted for their optimal use, in the hopes of solving multiple health and food conservation problems. This review aims to synthetize the information available nowadays regarding bacteriocins, and their classification, while also providing an insight into the future possibilities of their usage for both the pharmaceutical, food, and biotechnological industry.

ABSTRACT Due to the increasing incidence of antibiotic-resistant bacterial pathogens, the need for the development of alternative compounds is of utmost importance. Bacteriocins are considered a promising alternative to antibiotics. In this study, we determined the in vitro activities of 65 bacteriocins from the PARAGEN collection along with microbisporicin (NAI-107) against 14 WHO reference isolates of Neisseria gonorrhoeae, one isolate of Neisseria meningitidis, and four commensal Neisseria spp. The initial screening of the bacteriocins was carried out using a spot-on-lawn assay wherein 12 bacteriocins (12/66) showed a zone of inhibition against the WHO-P N. gonorrhoeae isolate. Four bacteriocins (4/12), Garvicin KS (GarKS) (ABC), lacticin (lcn) Q, lcn Z, and NAI-107, demonstrated higher activity, and minimum inhibitory concentrations (MICs) using agar dilutions were determined for 19 Neisseria spp. GarKS (ABC), lcn Q, and lcn Z had an MIC range of 4–16 µg/mL, whereas NAI-107 had an MIC range of

Antimicrobial resistance is one of the most significant threats to public health worldwide. As opposed to using traditional antibiotics, which are effective against diseases that are multidrug-resistant, it is vital to concentrate on the most innovative antibacterial compounds. These innate bacterial arsenals under the term «bacteriocins» refer to low-molecularweight, heat-stable, membrane-active, proteolytically degradable, and pore-forming cationic peptides. Due to their ability to attack bacteria, viruses, fungi, and biofilm, bacteriocins appear to be the most promising, currently accessible alternative for addressing the antimicrobial resistance (AMR) problem and minimizing the negative effects of antibiotics on the host's microbiome. Nano-compounds have shown promise in a variety of applications, including antibacterial agents, drug delivery systems, food and drug packaging elements, functional food formulations, and many more. However, there are certain disadvantages in the chemical production of nanoparticles (NPs), such as toxicity and other negative impacts. Due to the dual action of biological sources combined with metallic NPs, the use of conjugated or green-synthesized nanoparticles has become more widespread during the past ten years. Recently, bacteriocin nanoparticles have emerged as a viable remedy and the most effective antibacterial agent in vitro to overcome some of these limitations. [ABSTRACT FROM AUTHOR]

The skin microbiome is mainly comprised of commensal and mutualistic bacteria. Some commensal species can behave as pathogens under the right circumstances, and one of the most common examples of this is Staphylococcus aureus. This bacterium can damage multiple parts and systems of the human body, both directly and indirectly. The factors responsible for the pathogenesis of S. aureus are discussed in this article, along with its particular role in the skin disorder atopic dermatitis, shedding light on how bacteria can use complex strategies to survive in a host. [ABSTRACT FROM AUTHOR]

Nisin is a naturally occurring bioactive small peptide produced by Lactococcus lactis subsp. lactis and belongs to the Type A (I) lantibiotics. Due to its potent antimicrobial activity, it has been broadly employed to preserve various food materials as well as to combat a variety of microbial pathogens. The present review discusses the antimicrobial properties of nisin and different types of their derivatives employed to treat microbial pathogens with a detailed underlying mechanism of action. Several alternative strategies such as combination, conjugation, and nanoformulations have been discussed in order to address several issues such as rapid degradation, instability, and reduced activity due to the various environmental factors that arise in the applications of nisin. Furthermore, the evolutionary relationship of many nisin genes from different nisin-producing bacterial species has been investigated. A detailed description of the natural and bioengineered nisin variants, as well as the underlying action mechanisms, has also been provided. The chemistry used to apply nisin in conjugation with natural or synthetic compounds as a synergetic mode of antimicrobial action has also been thoroughly discussed. The current review will be useful in learning about recent and past research that has been performed on nisin and its derivatives as antimicrobial agents. [ABSTRACT FROM AUTHOR]

Keypoints Taxonomically distant species have a wide diversity of roseocin family lantibiotics. The phylogeny-guided approach opens new possibilities for RiPPs bioengineering. Bioactive variants of roseocin were generated using semi-in vitro reconstitution.

Lantibiotics are believed to have a conceivable potential to be used as therapeutics, especially against clinically resistant bacterial strains. However, their low solubility and poor stability under physiological conditions limit their availability for clinical studies and further pharmaceutical commercialization. Nisin is a readily available and cheap lanthipeptide and thus serves as a good model in the search for the tools to engineer lantibiotics with improved pharmacological properties. This review aims to address technologies that can be applied to alter and enhance the antimicrobial activity, antibacterial spectrum and physicochemical properties (solubility, solution stability and protease resistance) of nisin. There are basically two general means to obtain nisin analogs—protein engineering and chemical functionalization of this antibiotic. Although bioengineering techniques have been well developed and enable the creation of nisin mutants of variable structures and properties, they are lacking spectacular effects so far. Chemical modifications of nisin based on utilization of the reactivity of its free amino and carboxylic moieties, as well as reactivity of the double bonds of its dehydroamino acids, are in their infancy. [ABSTRACT FROM AUTHOR]

Lantibiotics are ribosomally synthesized and posttranslationally modified peptides (RiPPs) that are produced by bacteria. Interest in this group of natural products is increasing rapidly as alternatives to conventional antibiotics. Some human microbiome-derived commensals produce lantibiotics to impair pathogens' colonization and promote healthy microbiomes. Streptococcus salivarius is one of the first commensal microbes to colonize the human oral cavity and gastrointestinal tract, and its biosynthesis of RiPPs, called salivaricins, has been shown to inhibit the growth of oral pathogens. Herein, we report on a phosphorylated class of three related RiPPs, collectively referred to as salivaricin 10, that exhibit proimmune activity and targeted antimicrobial properties against known oral pathogens and multispecies biofilms. Strikingly, the immunomodulatory activities observed include upregulation of neutrophil-mediated phagocytosis, promotion of antiinflammatory M2 macrophage polarization, and stimulation of neutrophil chemotaxis--these activities have been attributed to the phosphorylation site identified on the N-terminal region of the peptides. Salivaricin 10 peptides were determined to be produced by S. salivarius strains found in healthy human subjects, and their dual bactericidal/antibiofilm and immunoregulatory activity may provide new means to effectively target infectious pathogens while maintaining important oral microbiota. [ABSTRACT FROM AUTHOR]

Nisin is the most well-known representative of subtype A1 lantibiotics. This small (< 5 kDa) peptide ribosomally produced by Gram-positive bacteria belonging to Lactococcus, Streptococcus, Staphylococcus and Blautia species. Nisin exhibits antibacterial activity against a broad range of Gram-positive bacteria and may be effective against Gram-negative pathogens. For analytical semi-preparative purposes, gradient HPLC is often used in the acetonitrile concentration range from 20 to 30 % (solvent B) and a retention time of 20 to 50 min. In this study the optimal conditions for the analysis of nisin by RP-HPLC were determined: a gradient from 23 to 28 % acetonitrile (buffer B) when used as solvents: buffer A: [4 M LiClO4 - 0.1 M HClO4 ]: H2O=1:19; and buffer B: 100 % CH3CN with a retention time up to 12 min. Differences between the chromatographic profiles of expired and non-expired nisin samples have been identified. The expired nisin sample differs from the non-expired samples by the presence of asymmetric nisin A / Z peaks with significant degradation of the nisin A peak. The results of the study indicate the possibility using RP-HPLC for checking the quality and shelf life of commercial nisin samples without the need for additional purification. [ABSTRACT FROM AUTHOR]

Roseocin, the two-peptide lantibiotic from Streptomyces roseosporus, carries extensive intramolecular (methyl)lanthionine bridging in the peptides and exhibits synergistic antibacterial activity against clinically relevant Gram-positive pathogens. Both peptides have a conserved leader but a diverse core region. The biosynthesis of roseocin involves post-translational modification of the two precursor peptides by a single promiscuous lanthipeptide synthetase, RosM, to install an indispensable disulfide bond in the Rosα core along with four and six thioether rings in Rosα and Rosβ cores, respectively. RosM homologs in the phylum actinobacteria were identified here to reveal twelve other members of the roseocin family which diverged into three types of biosynthetic gene clusters (BGCs). Further, the evolutionary rate among the BGC variants and analysis of variability within the core peptide versus leader peptide revealed a phylum-dependent lanthipeptide evolution. Analysis of horizontal gene transfer revealed its role in the generation of core peptide diversity. The naturally occurring diverse congeners of roseocin peptides identified from the mined novel BGCs were carefully aligned to identify the conserved sites and the substitutions in the core peptide region. These selected sites in the Rosα peptide were mutated for permitted substitutions, expressed heterologously in E. coli, and post-translationally modified by RosM in vivo. Despite a limited number of generated variants, two variants, RosαL8F and RosαL8W exhibited significantly improved inhibitory activity in a species-dependent manner compared to the wild-type roseocin. Our study proves that a natural repository of evolved variants of roseocin is present in nature and the key variations can be used to generate improved variants. Keypoints: Taxonomically distant species have a wide diversity of roseocin family lantibiotics. The phylogeny-guided approach opens new possibilities for RiPPs bioengineering. Bioactive variants of roseocin were generated using semi-in vitro reconstitution. [ABSTRACT FROM AUTHOR]

The enzymatic machinery involved in the biosynthesis of lantibiotic is an untapped source of proteases with different specificities. Lanthipeptide biosynthesis requires proteolysis of specific target sequences by known proteases, which are encoded by contiguous genes. Herein, the activity of lichenicidin A2 (LicA2) trimming proteases (LicP and LicT) was investigated in vivo. Firstly, the impact of some residues and the size of the peptide were evaluated. Then followed trials in which LicA2 leader was evaluated as a tag to direct production and secretion of other relevant peptides. Our results show that a negatively charged residue (preferably Glu) at cleavage site is important for LicP efficacy. Some mutations of the lichenicidin hexapeptide such as Val-4Ala, Asp-5Ala, Asn-6Ser, and the alteration of GG-motif to GA resulted in higher processing rates, indicating the possibility of improved lichenicidin production in Escherichia coli. More importantly, insulin A, amylin (non-lanthipeptides), and epidermin were produced and secreted to E. coli supernatant, when fused to the LicA2 leader peptide. This work aids in clarifying the activity of lantibiotic-related transporters and proteases and to evaluate their possible application in industrial processes of relevant compounds, taking advantage of the potential of microorganisms as biofactories. Key points: • LicM2 correct activity implies a negatively charged residue at position -1. • Hexapeptide mutations can increase the amount of fully processed Bliβ. • LicA2 leader peptide directs LicTP cleavage and secretion of other peptides. [ABSTRACT FROM AUTHOR]

Ferroptosis is an iron dependent form of cell death, that is triggered by the discoordination of iron, lipids, and thiols. Its unique signature that distinguishes it from other forms of cell death is the formation and accumulation of lipid hydroperoxides, particularly oxidized forms of polyunsaturated phosphatidylethanolamines (PEs), which drives cell death. These readily undergo iron-catalyzed secondary free radical reactions leading to truncated products which retain the signature PE headgroup and which can readily react with nucleophilic moieties in proteins via their truncated electrophilic acyl chains. Using a redox lipidomics approach, we have identified oxidatively-truncated PE species (trPEox) in enzymatic and non-enzymatic model systems. Further, using a model peptide we demonstrate adduct formation with Cys as the preferred nucleophilic residue and PE(26:2) +2 oxygens, as one of the most reactive truncated PE-electrophiles produced. In cells stimulated to undergo ferroptosis we identified PE-truncated species with sn-2 truncations ranging from 5 to 9 carbons. Taking advantage of the free PE headgroup, we have developed a new technology using the lantibiotic duramycin, to enrich and identify the PE-lipoxidated proteins. Our results indicate that several dozens of proteins for each cell type, are PE-lipoxidated in HT-22, MLE, and H9c2 cells and M2 macrophages after they were induced to undergo ferroptosis. Pretreatment of cells with the strong nucleophile, 2-mercaptoethanol, prevented the formation of PE-lipoxidated proteins and blocked ferroptotic death. Finally, our docking simulations showed that the truncated PE species bound at least as good to several of the lantibiotic-identified proteins, as compared to the non-truncated parent molecule, stearoyl-arachidonoyl PE (SAPE), indicating that these oxidatively-truncated species favor/promote the formation of PEox-protein adducts. The identification of PEox-protein adducts during ferroptosis suggests that they are participants in the ferroptotic process preventable by 2-mercaptoethanol and may contribute to a point of no return in the ferroptotic death process.

Background. The increasing role of coagulase-negative staphylococci in the occurrence of staphylococcal infections leads to the need for close attention to them. Special control is required over the sensitivity of bacteria to antibiotics and the spread of methicillin resistance, as a sign of multiple resistance to antibacterial drugs. It is also important to identify the virulence factors of coagulase-negative staphylococci, which determine their behavior in the environment.The aim. To evaluate the sensitivity of strains of coagulase-negative staphylococci to clinically significant antibiotics daptomycin, vancomycin, linezolid and oxacillin and lantibiotic warnerin.Methods. Determination of the minimal inhibitory concentrations of antibacterial compounds for clinical coagulase-negative staphylococci by standard methods of serial dilutions and disc diffusion. Identification of the phenomenon of decreased susceptibility of bacteria to vancomycin by population analysis and concentration gradient. Lipid analysis by thin layer chromatography. Results. High antibacterial activity of vancomycin, daptomycin and linezolid against clinical strains of coagulase-negative staphylococci was shown. The upper limit of the minimum inhibitory concentrations of vancomycin within the sensitive phenotype and the expansion of the ranges of the minimum inhibitory concentrations of daptomycin and warnerin towards an increase in oxacillin-resistant isolates were revealed. The heterogeneous nature of sensitivity to vancomycin of the cultures of the studied strains and the possibility of their rapid enrichment with subpopulations with reduced sensitivity to this antibiotic have been established. The selection of resistance of coagulase-negative staphylococci to vancomycin was accompanied by an increase in the synthesis of lysylphosphatidylglycerol and a decrease in their sensitivity to cationic peptide compounds.Conclusion. The revealed prevalence of the methicillin-resistant phenotype of clinical strains of coagulase-negative staphylococci, along with the presence in the lipid spectrum of the universal factor of resistance to cationic antibacterial compounds, lysylphosphatidylglycerol, entails the need for new methodological solutions for diagnosing infections caused by coagulase-negative staphylococci.

In both eukarya and bacteria, the addition of Cys to dehydroalanine (Dha) and dehydrobutyrine (Dhb) occurs in various biological processes. In bacteria, intramolecular thia-Michael addition catalyzed by lanthipeptide cyclases (LanC) proteins or protein domains gives rise to a class of natural products called lanthipeptides. In eukarya, dehydroamino acids in signaling proteins are introduced by effector proteins produced by pathogens like Salmonella to dysregulate host defense mechanisms. A eukaryotic LanC-like (LanCL) enzyme catalyzes the addition of Cys in glutathione to Dha/Dhb to protect the cellular proteome from unwanted chemical and biological activity. To date, the mechanism of the enzyme-catalyzed thia-Michael addition has remained elusive. We report here the crystal structures of the human LanCLl enzyme complexed with different ligands, including the product of thia-Michael addition of glutathione to a Dhb-containing peptide that represents the activation loop of Erk. The structures show that a zinc ion activates the Cys thiolate for nucleophilic attack and that a conserved His is poised to protonate the enolate intermediate to achieve a net anti-addition. A second His hydrogen bonds to the carbonyl oxygen of the former Dhb and may stabilize the negative charge that builds up on this oxygen atom in the enolate intermediate. Surprisingly, the latter His is not conserved in orthologous enzymes that catalyze thia-Michael addition to Dha/Dhb. Eukaryotic LanCLs contain a His, whereas bacterial stand-alone LanCs have a Tyr residue, and LanM enzymes that have LanC-like domains have a Lys, Asn, or His residue. Mutational and binding studies support the importance of these residues for catalysis. [ABSTRACT FROM AUTHOR]

To date, a number of lantibiotics have been shown to use lipid II—a highly conserved peptidoglycan precursor in the cytoplasmic membrane of bacteria—as their molecular target. The α-component (Lchα) of the two-component lantibiotic lichenicidin, previously isolated from the Bacillus licheniformis VK21 strain, seems to contain two putative lipid II binding sites in its N-terminal and C-terminal domains. Using NMR spectroscopy in DPC micelles, we obtained convincing evidence that the C-terminal mersacidin-like site is involved in the interaction with lipid II. These data were confirmed by the MD simulations. The contact area of lipid II includes pyrophosphate and disaccharide residues along with the first isoprene units of bactoprenol. MD also showed the potential for the formation of a stable N-terminal nisin-like complex; however, the conditions necessary for its implementation in vitro remain unknown. Overall, our results clarify the picture of two component lantibiotics mechanism of antimicrobial action. [ABSTRACT FROM AUTHOR]

ABSTRACT Owing to extensive metagenomic studies, we now have access to numerous sequences of novel bacteriocin-like antimicrobial peptides encoded by various cultivable and noncultivable bacteria. However, relatively rarely, we even have access to these cultivable strains to examine the potency and the targets of the predicted bacteriocins. In this study, we evaluated a heterologous biosynthetic system to produce biologically active nonnative novel lantibiotics, which are modified bacteriocins. We chose Streptococcus mutans, a dental pathogen, as the host organism because it is genetically easy to manipulate and is inherently a prolific producer of various bacteriocins. We chose the S. mutans T8 strain as the host, which produces the lantibiotic mutacin II, to express 10 selected homologs of mutacin II identified from GenBank. These lantibiotic peptides either are novel or have been studied very minimally. The core regions of the selected lantibiotic peptides were fused to the leader sequence of the mutacin II peptide and integrated into the chromosome such that the core region of the native mutacin II was replaced with the new core sequences. By this approach, using the mutacin II biosynthesis machinery, we obtained one bioactive novel lantibiotic peptide with 52% different residues compared to the mutacin II core region. This unknown lantibiotic is encoded by Streptococcus agalactiae and Streptococcus ovuberis strains. Since this peptide displays some homology with nukacin ISK-1, we named it nukacin Spp. 2. This study demonstrated that the mutacin II biosynthesis machinery can be successfully used as an efficient system for the production of biologically active novel lantibiotics. IMPORTANCE In this study, we report for the first time that Streptococcus mutans can be used as a host to produce various nonnative lantibiotics. We showed that in the T8 strain, we could produce bioactive lacticin 481 and nukacin ISK-1, both of which are homologs of mutacin II, using T8’s modification and secretion apparatus. Similarly, we also synthesized a novel bioactive lantibiotic, which we named nukacin Spp. 2.

Mutacin 1140 (Mu1140) is a potent antibiotic against Gram-positive bacteria, such as Staphylococcus aureus. The antibiotic is produced by the oral bacterium Streptococcus mutans and is a member of the epidermin family of type AI lantibiotics. The antibiotic exerts its inhibitory activity by binding to the cell wall precursor lipid II, blocking cell wall synthesis, and by disrupting bacterial membranes. In previous studies, the novel K2A and R13A analogs of Mu1140 have been identified to have superior pharmacokinetic properties compared to native Mu1140. In this study, the use of a combined formulation of the Mu1140 K2A and R13A analogs was shown to be more effective at treating MRSA bacteremia than the native Mu1140 or vancomycin. The analogs were also shown to be effective in treating an MRSA skin infection. The use of K2A and R13A analogs may provide a future alternative for treating serious Gram-positive bacterial infections. In a previous study, the Mu1140 analogs were shown to have significantly longer drug clearance times, leading to higher plasma concentrations over time. These properties warranted further testing to determine whether the analogs are effective for the treatment of systemic MRSA and acute skin infections. In this study, Mu1140 analogs were shown to be more effective than currently available treatments for systemic and skin MRSA infections. Further, the study clearly shows that the new analogs are superior to native Mu1140 for the treatment of a systemic MRSA infection. These findings support continued drug product development efforts using the K2A and R13A Mu1140 analogs, and that these analogs may ameliorate the outcome of serious bacterial infections.

Emerging evidence emphasizes the functional impacts of host microbiome on the etiopathogenesis of autoimmune diseases, including rheumatoid arthritis (RA). However, there are limited mechanistic insights into the contribution of microbial biomolecules especially microbial peptides toward modulating immune homeostasis. Here, by mining the metagenomics data of tonsillar microbiome, a deficiency of the encoding genes of lantibiotic peptides salivaricins in RA patients is identified, which shows strong correlation with circulating immune cells. Evidence is provided that the salivaricins exert immunomodulatory effects in inhibiting T follicular helper (Tfh) cell differentiation and interleukin‐21 (IL‐21) production. Mechanically, salivaricins directly bind to and induce conformational changes of IL‐6 and IL‐21 receptors, thereby inhibiting the bindings of IL‐6 and IL‐21 to their receptors and suppressing the downstream signaling pathway. Finally, salivaricin administration exerts both prophylactic and therapeutic effects against experimental arthritis in a murine model of RA. Together, these results provide a mechanism link of microbial peptides‐mediated immunomodulation. [ABSTRACT FROM AUTHOR]

Emerging diseases in aquaculture are creating havoc on the industry's profitability and productivity due to climate stress and shifting conditions. It creates scarcity to meet the global food market's demand. Infections in aqua farms are unavoidable due to various factors that can cause sudden disease outbreaks among farmed species. Farmers all over the world are using antibiotics to combat the crisis, which leads to the development of resistance in susceptible pathogens. This review suggests the use of lantibiotics as an alternative antibiotic agent or natural antibiotic in aquaculture to treat and manage diseases. Till now, more than 60 lantibiotics have been discovered. The biosynthesis and mechanism of all the lantibiotics are similar except differences in their gene cluster. This review discusses the classification of lantibiotics, biosynthesis, mode of action, and potential of lantibiotics' battle against Gram-positive or Gram-negative bacteria, various sources of lantibiotics including aquatic and non-aquatic environments and bioengineered lantibiotics with their increased potential against varieties of pathogens including antibiotic-resistant strains. Aquatic and non-aquatic lantibiotics had shown efficient activity against various infectious microbes causing disease in aquaculture organisms. This review provides knowledge on these lantibiotics, which is required to use them as an alternative therapeutic agent for the treatment of aquaculture diseases. [ABSTRACT FROM AUTHOR]

Anatomical and physiological considerations indicate that the oral cavity is a primary source of the lung microbiota community, and recent studies have shown that the microbiota in the lungs contributes to immunological homeostasis, potentially altering the organ's susceptibility to viral infection, including SARS-CoV-2. It has been proposed that, in the case of viral infection, lung Gram-negative bacteria could promote the cytokine cascade with a better performance than a microbiota mainly constituted by Gram-positive bacteria. Recent observations also suggest that Prevotella-rich oral microbiotas would dominate the oral cavity of SARS-CoV-2-infected patients. In comparison, Streptococcus-rich microbiotas would dominate the oral cavity of healthy people. To verify if the modulation of the oral microbiota could have an impact on the current coronavirus disease, we administered for 14 days a well-recognized and oral-colonizing probiotic (S. salivarius K12) to hospitalized COVID-19 patients. The preliminary results of our randomized and controlled trial seem to prove the potential role of this oral strain in improving the course of the main markers of pathology, as well as its ability to apparently reduce the death rate from COVID-19. Although in a preliminary and only circumstantial way, our results seem to confirm the hypothesis of a direct involvement of the oral microbiota in the construction of a lung microbiota whose taxonomic structure could modulate the inflammatory processes generated at the pulmonary and systemic level by a viral infection. [ABSTRACT FROM AUTHOR]

Abstract Emerging evidence emphasizes the functional impacts of host microbiome on the etiopathogenesis of autoimmune diseases, including rheumatoid arthritis (RA). However, there are limited mechanistic insights into the contribution of microbial biomolecules especially microbial peptides toward modulating immune homeostasis. Here, by mining the metagenomics data of tonsillar microbiome, a deficiency of the encoding genes of lantibiotic peptides salivaricins in RA patients is identified, which shows strong correlation with circulating immune cells. Evidence is provided that the salivaricins exert immunomodulatory effects in inhibiting T follicular helper (Tfh) cell differentiation and interleukin‐21 (IL‐21) production. Mechanically, salivaricins directly bind to and induce conformational changes of IL‐6 and IL‐21 receptors, thereby inhibiting the bindings of IL‐6 and IL‐21 to their receptors and suppressing the downstream signaling pathway. Finally, salivaricin administration exerts both prophylactic and therapeutic effects against experimental arthritis in a murine model of RA. Together, these results provide a mechanism link of microbial peptides‐mediated immunomodulation.

Lantibiotics are believed to have a conceivable potential to be used as therapeutics, especially against clinically resistant bacterial strains. However, their low solubility and poor stability under physiological conditions limit their availability for clinical studies and further pharmaceutical commercialization. Nisin is a readily available and cheap lanthipeptide and thus serves as a good model in the search for the tools to engineer lantibiotics with improved pharmacological properties. This review aims to address technologies that can be applied to alter and enhance the antimicrobial activity, antibacterial spectrum and physicochemical properties (solubility, solution stability and protease resistance) of nisin. There are basically two general means to obtain nisin analogs—protein engineering and chemical functionalization of this antibiotic. Although bioengineering techniques have been well developed and enable the creation of nisin mutants of variable structures and properties, they are lacking spectacular effects so far. Chemical modifications of nisin based on utilization of the reactivity of its free amino and carboxylic moieties, as well as reactivity of the double bonds of its dehydroamino acids, are in their infancy.

Nisin is an antibacterial peptide with anticancer properties, but the main drawback is its rapid enzymatic degradation and limited permeation across the cell membrane. This research aims to overcome these drawbacks by developing nisin-loaded nanoparticles (NPN) with improved cytotoxic effects. PLGA nanoparticles are one of the most effective biodegradable and biocompatible drug delivery carriers. In the present study, nisin-loaded nanoparticles showed enhanced anticancer effects. NPN was prepared by a double emulsion solvent evaporation method and characterized for different parameters. The cytotoxic investigation of NPN was carried out on various cell lines, including A549, SW-620, HT-29, PC-3, MDA-MB-231, MCF-7, MiaPaca-2, and fR2 by sulforhodamine B (SRB) assay. Mechanistic investigation of cellular cytotoxicity was performed by using bright-field microscopy, DAPI staining, intracellular reactive oxygen species (ROS), changes in mitochondrial membrane potential (ΔΨm), Western blotting and cellular uptake study. A comparative cytotoxicity study of nisin and NPN was performed on normal breast epithelial cells (fR2). NPN showed spherical shape, 289.09 ± 3.63 nm particle size, and 63.37 ± 3.12% entrapment efficiency. NPN was more cytotoxic to the MDA-MB-231 cell line, showing higher nuclear fragmentation, ROS generation, depletion of ΔΨm, and enhanced intracellular uptake with apoptosis signs compared with nisin and with no cytotoxicity on normal cells. The findings suggest that nisin delivery via PLGA nanoparticles can be used to treat cancer without significant effects on healthy cells. [ABSTRACT FROM AUTHOR]

The role of various membrane components, phospholipids and lipopolysaccharides, in the formation and functioning of ion channels formed by lantibiotics of class A, nisin, and class B, cinnamycin and duramycin, was studied. Threshold concentrations of the tested lantibiotics were determined that cause ion channel formation and destruction of planar lipid bilayers. It was found that nisin was able to form ion channels with a conductance in the range from 2 to 600 pS at a concentration of more than 40 μM both in negatively charged lipid bilayers containing a specific adjuvant of gram-negative bacterial membranes, Kdo2–lipid A, and in cardiolipin-containing membranes. The obtained results allowed suggesting that in model lipid membranes without lipid II, a precursor of peptidoglycan of gram-positive bacteria, which is a specific receptor of nisin, its role can be performed by Kdo2–lipid A and cardiolipin. It was found that cinnamycin and its close analogue duramycin at concentrations of 1.5–3 μM induced step-like current fluctuations corresponding to the functioning of single ion channels with amplitudes from 5 to 30 pS and from 50 to 900 pS in membranes of phosphatidylethanolamine and cardiolipin-enriched bilayers, respectively. Based on the results obtained, we conclude that the channel-forming ability of cinnamycin and duramycin depends on the presence in the membrane of lipids prone to the formation of inverted hexagonal phases and the induction of spontaneous negative curvature in lipid monolayers. [ABSTRACT FROM AUTHOR]

Antimicrobial peptides (AMPs) are inherently occurring proteins that are produced by microorganisms as secondary metabolites. Members of genus Bacillus produce many types of AMPs by ribosomal (bacteriocins) and non-ribosomal (polymyxins and iturins) mechanisms. Bacteriocins are ribosomally synthesized peptides that inhibit the growth of closely related bacterial strains. Moreover, bacteriocins produced by Bacillus species have been widely used in pharmaceutical, food industry, fishery, livestock as well as in agriculture sector. The objective of this review is to assess the characterization of the Bacillus-derived bacteriocins, their potential use in different sectors and structure-activity relationships. [ABSTRACT FROM AUTHOR]

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Lanthipeptides are a group of ribosomally synthesized and post‐translationally modified peptides with diverse structural features and bioactivities. Gut‐microbiota‐derived lanthipeptides play important roles in gut homeostasis of the host. Herein, we report the discovery and biosynthesis of class III lantibiotics named amylopeptins, which are derived from the gut microbiota of Sprague‐Dawley rats and display a narrow antimicrobial spectrum. In contrast to known class III lanthipeptides, the biosynthesis of amylopeptins employs AmyP, which belongs to a subgroup of S8 family serine proteases, to remove the leader of corresponding precursor peptides in a site‐specific manner during the last step of their maturation. Overall, this study shows for the first time that S8 family proteases participate in the biosynthesis of class III lanthipeptides. [ABSTRACT FROM AUTHOR]

Milk, due to its high nutritional content, is an excellent medium for supporting growth of diverse group of microorganisms, many of which produce beneficial compounds like bacteriocins. Class I bacteriocins, called lantibiotics, are ribosomally synthesized, post-translationally modified peptides containing unusual amino acids, such as dehydrated and lanthionine residues with antibacterial activities. Bacterial strains isolated from milk and dairy products produce a range of lantibiotics which can employed for development of food preservatives, flavor enhancers and as alternate treatment strategies for multi drug resistant bacterial pathogens. The diverse category of lantibiotics from milk isolates include well characterized prototypes like nisin to newer peptides yet to be studied. In this review, details of most prominent lantibiotics obtained from milk isolates have been presented with special focus on applications of these lantibiotics in therapeutics and food. [ABSTRACT FROM AUTHOR]

Lantibiotics are a promising class of natural antimicrobial peptides. Lichenicidin is a two-peptide lantibiotic in which two mature peptides act synergistically to exhibit full bioactivity. Considering the two-peptide lantibiotics described so far, only cytolysin has been deeply characterized in terms of toxicity towards eukaryotic cells and it was found to be hemolytic and cytotoxic. This work aimed to improve the production of lichenicidin in vivo and characterize its antibacterial activity and toxicity against human cells. Peptides were purified and minimal inhibitory concentration (MIC) was determined against several strains; a time-kill assay was performed with Staphylococcus aureus. The hemolytic effect of lichenicidin was evaluated on blood samples from healthy donors and its toxicity towards human fibroblasts. The quantity of purified peptides was 1 mg/l Bliα and 0.4 mg/l Bliβ. MIC for methicillin-sensitive and resistant S. aureus (MSSA and MRSA) strains were 16–32 µg/ml and 64–128 µg/ml, respectively. At the MIC, lichenicidin took less than 3 h to eliminate MSSA, indicating a strong bactericidal effect. It induces cell lysis at the highest concentration, an effect that might be potentiated by Bliβ. Lichenicidin was not cytotoxic to human erythrocytes and fibroblasts. In this work, we evaluated the therapeutic potential of lichenicidin as a possible antimicrobial alternative. [ABSTRACT FROM AUTHOR]

Cell division is a central process in bacteria and a prerequisite for pathogenicity. Several proteins are involved in this process to ensure the accurate localization and proper function of the division machinery. In Streptococcus mutans, MapZ marks the division sites and position of the Z‐ring to regulate cell division; however, whether MapZ deficiency can impair the cariogenic virulence of S. mutans remains unclear. Here, using a phenotypic assay and RNA‐seq, we investigated the role of MapZ in cell envelope maintenance, biofilm formation, and stress tolerance in S. mutans. The results show that MapZ is important for normal cell shape and envelope structure, and its deletion causes abnormal septum structure and a thin cell wall. Subsequently, we found that the absence of MapZ leads to a greater level of cell death within 12 h biofilms, but it does not seem to affect biofilm architecture and accumulation. mapZ deletion also results in a decreased acid and osmotic stress tolerance. Furthermore, RNA‐seq data reveal that MapZ deficiency causes changes in the expression levels of genes involved in transport systems, sugar metabolism, nature competence, and bacteriocin synthesis. Interestingly, we found that mapZ mutation renders S. mutans more sensitive to chlorhexidine. Taken together, our study suggests that MapZ plays a role in maintaining cell envelope structure and stress tolerance in S. mutans, showing a potential application as a drug target for caries prevention. [ABSTRACT FROM AUTHOR]

Antimicrobial resistance presents a substantial threat to global public health, demanding urgent attention and action. This study focuses on lanthipeptides, ribosomally encoded peptides that display significant structural diversity and hold promising potential as antibiotics. Genome mining was employed to locate biosynthetic gene clusters (BGCs) containing class II lanthipeptide synthetases encoded by lanM genes. A phylogenetic study analyzing homologous sequences of functional LanM sequences revealed a unique evolutionary clade of 17 LanM proteins associated with 12 Clostridium bacterial genomes. In silico exploration identified nine complete BGCs, including one super-cluster containing two co-localized operons from Clostridium cellulovorans 743B, that encode for two new peptides named clostrisin and cellulosin. Each operon was heterologously expressed in Escherichia coli . Molecular weights associated with the expected post-translational modifications of the purified lanthipeptide were confirmed by MS-MS/MS analysis for cellulosin, while clostrisin was not post-translationally modified. Both peptides demonstrated antimicrobial activity against multidrug-resistant bacteria, such as a clinical strain of Staphylococcus epidermidis MIQ43 and Pseudomonas aeruginosa PA14. This is the first report of lanthipeptides from the Clostridium genus produced with its native biosynthetic machinery, as well as chemically and biologically characterized. This study showcases the immense potential of genome mining in identifying new RiPP synthetases and associated bioactive peptides., (Copyright © 2024, Alejo Hernandez et al.)

Anatomical and physiological considerations indicate that the oral cavity is a primary source of the lung microbiota community, and recent studies have shown that the microbiota in the lungs contributes to immunological homeostasis, potentially altering the organ’s susceptibility to viral infection, including SARS-CoV-2. It has been proposed that, in the case of viral infection, lung Gram-negative bacteria could promote the cytokine cascade with a better performance than a microbiota mainly constituted by Gram-positive bacteria. Recent observations also suggest that Prevotella-rich oral microbiotas would dominate the oral cavity of SARS-CoV-2-infected patients. In comparison, Streptococcus-rich microbiotas would dominate the oral cavity of healthy people. To verify if the modulation of the oral microbiota could have an impact on the current coronavirus disease, we administered for 14 days a well-recognized and oral-colonizing probiotic (S. salivarius K12) to hospitalized COVID-19 patients. The preliminary results of our randomized and controlled trial seem to prove the potential role of this oral strain in improving the course of the main markers of pathology, as well as its ability to apparently reduce the death rate from COVID-19. Although in a preliminary and only circumstantial way, our results seem to confirm the hypothesis of a direct involvement of the oral microbiota in the construction of a lung microbiota whose taxonomic structure could modulate the inflammatory processes generated at the pulmonary and systemic level by a viral infection.

Lanthipeptides are ribosomally synthesized and posttranslationally modified peptides, with modifications that are incorporated during biosynthesis by dedicated enzymes. Various modifications of the peptides are possible, resulting in a highly diverse group of bioactive peptides that offer a potential reservoir for use in the fight against a plethora of diseases. Their activities range from the antimicrobial properties of lantibiotics, especially against antibiotic-resistant strains, to antiviral activity, immunomodulatory properties, antiallodynic effects, and the potential to alleviate cystic fibrosis symptoms. Lanthipeptide biosynthetic genes are widespread within bacterial genomes, providing a substantial repository for novel bioactive peptides. Using genome mining tools, novel bioactive lanthipeptides can be identified, and coupled with rapid screening and heterologous expression technologies, the lanthipeptide drug discovery pipeline can be significantly sped up. Lanthipeptides represent a group of bioactive peptides that hold great potential as biotherapeutics, especially at a time when novel and more effective therapies are required. With this review, we provide insight into the latest developments made toward the therapeutic applications and production of lanthipeptides, specifically looking at heterologous expression systems. [ABSTRACT FROM AUTHOR]

Here we report a jute endophyte Staphylococcus hominis strain MBL_AB63 isolated from jute seeds which showed promising antimicrobial activity against Staphylococcus aureus SG511 when screening for antimicrobial substances. The whole genome sequence of this strain, annotated using BAGEL4 and antiSMASH 5.0 to predict the gene clusters for antimicrobial substances identified a novel antimicrobial peptide cluster that belongs to the class I lantibiotic group. The predicted lantibiotic (homicorcin) was found to be 82% similar to a reported peptide epicidin 280 having a difference of seven amino acids at several positions of the core peptide. Two distinct peaks obtained at close retention times from a RP-HPLC purified fraction have comparable antimicrobial activities and LC–MS revealed the molecular mass of these peaks to be 3046.5 and 3043.2 Da. The presence of an oxidoreductase (homO) similar to that of epicidin 280- associated eciO or epilancin 15X- associated elxO in the homicorcin gene cluster is predicted to be responsible for the reduction of the first dehydrated residue dehydroalanine (Dha) to 2-hydroxypropionate that causes an increase of 3 Da mass of homicorcin 1. Trypsin digestion of the core peptide and its variant followed by ESI–MS analysis suggests the presence of three ring structures, one in the N-terminal and other two interlocking rings at the C-terminal region that remain undigested. Homicorcin exerts bactericidal activity against susceptible cells by disrupting the integrity of the cytoplasmic membrane through pore formation as observed under FE-SEM. [ABSTRACT FROM AUTHOR]

Lactic acid bacteria (LAB) naturally inhibit the growth of other closely related bacteria by producing antimicrobial peptides called 'bacteriocins'. Bacteriocins are heat stable, food-safe, and potently inhibit numerous food spoilage as well as pathogenic bacteria. Most importantly, bacteriocins are rapidly degraded by gastric enzymes, and there are no reports on the development of antimicrobial resistance to them by the pathogenic bacteria. These features have attracted the attention of researchers to study bacteriocins for their fundamental properties and possible applications as next-generation antimicrobial agents. [ABSTRACT FROM AUTHOR]

ABSTRACT Nisin, a class I lantibiotic, is synthesized as a precursor peptide by a putative membrane-associated lanthionine synthetase complex consisting of the dehydratase NisB, the cyclase NisC, and the ABC transporter NisT. Here, we characterize the subcellular localization and the assembly process of the nisin biosynthesis machinery in Lactococcus lactis by mutational analyses and fluorescence microscopy. Precursor nisin, NisB, and NisC were found to be mainly localized at the cell poles, with a preference for the old poles. They were found to be colocalized at the same spots in these old pole regions, functioning as a nisin modification complex. In contrast, the transporter NisT was found to be distributed uniformly and circumferentially in the membrane. When nisin secretion was blocked by mutagenesis of NisT, the nisin biosynthesis machinery was also visualized directly at a polar position using fluorescence microscopy. The interactions between NisB and other components of the machinery were further studied in vivo, and therefore, the “order of assembly” of the complex was revealed, indicating that NisB directly or indirectly plays the role of a polar “recruiter” in the initial assembly process. Additionally, a potential domain that is located at the surface of the elimination domain of NisB was identified to be crucial for the polar localization of NisB. Based on these data, we propose a model wherein precursor nisin is first completely modified by the nisin biosynthesis machinery, preventing the premature secretion of partially modified peptides, and subsequently secreted by recruited NisT, preferentially at the old pole regions. IMPORTANCE Nisin is the model peptide for LanBC-modified lantibiotics that are commonly modified and exported by a putative synthetase complex. Although the mechanism of maturation, transport, immunity, and regulation is relatively well understood, and structural information is available for some of the proteins involved (B. Li, J. P. J. Yu, J. S. Brunzelle, G. N. Moll, et al., Science 311:1464–1467, 2006, https://doi.org/10.1126/science.1121422; M. A. Ortega, Y. Hao, Q. Zhang, M. C. Walker, et al., Nature 517:509–512, 2015, https://doi.org/10.1038/nature13888; C. Hacker, N. A. Christ, E. Duchardt-Ferner, S. Korn, et al., J Biol Chem 290:28869–28886, 2015, https://doi.org/10.1074/jbc.M115.679969; Y. Y. Xu, X. Li, R. Q. Li, S. S. Li, et al., Acta Crystallogr D Biol Crystallogr 70:1499–1505, 2014, https://doi.org/10.1107/S1399004714004234), the subcellular localization and assembly process of the biosynthesis complex remain to be elucidated. In this study, we determined the spatial distribution of nisin synthesis-related enzymes and the transporter, revealing that the modification and secretion of the precursor nisin mainly occur at the old cell poles of L. lactis and that the transporter NisT is probably recruited later to this spot after the completion of the modification reactions by NisB and NisC. Fluorescently labeled nisin biosynthesis machinery was visualized directly by fluorescence microscopy. To our knowledge, this is the first study to provide direct evidence of the existence of such a complex in vivo. Importantly, the elucidation of the “order of assembly” of the complex will facilitate future endeavors in the investigation of the nisin secretion mechanism and even the isolation and structural characterization of the complete complex.

Bacteria produce under certain stress conditions bacteriocins and microcins that display antibacterial activity against closely related species for survival. Bacteriocins and microcins exert their antibacterial activity by either disrupting the membrane or inhibiting essential intracellular processes of the bacterial target. To this end, they can lyse bacterial membranes and cause subsequent loss of their integrity or nutrients, or hijack membrane receptors for internalisation. Both bacteriocins and microcins are ribosomally synthesised and several are posttranslationally modified, whereas others are not. Such peptides are also toxic to the producer bacteria, which utilise immunity proteins or/and dedicated ATP‐binding cassette (ABC) transporters to achieve self‐immunity and peptide export. In this review, we discuss the structure and mechanism of self‐protection that is conferred by these ABC transporters. [ABSTRACT FROM AUTHOR]