Overproduction of wild-type and bioengineered derivatives of the lantibiotic lacticin 3147

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

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

Incorporation of Non-Canonical Amino Acids into Antimicrobial Peptides: Advances, Challenges, and Perspectives

The emergence of antimicrobial resistance is a global health concern and calls for the development of novel antibiotic agents. Antimicrobial peptides seem to be promising candidates due to their diverse sources, mechanisms of action, and physicochemical characteristics, as well as the relatively low emergence of resistance. The incorporation of noncanonical amino acids into antimicrobial peptides could effectively improve their physicochemical and pharmacological diversity. Recently, various antimicrobial peptides variants with improved or novel properties have been produced by the incorporation of single and multiple distinct noncanonical amino acids. In this review, we summarize strategies for the incorporation of noncanonical amino acids into antimicrobial peptides, as well as their features and suitabilities. Recent applications of noncanonical amino acid incorporation into antimicrobial peptides are also presented. Finally, we discuss the related challenges and prospects.

Library and post-translational modifications of peptide-based display systems

Innovative biotechnological methods empower the successful identification of new drug candidates. Phage, ribosome and mRNA display represent high throughput screenings, allowing fast and efficient progress in the field of targeted drug discovery. The identification range comprises low molecular weight peptides up to whole antibodies. However, a major challenge poses the stability and affinity in particular of peptides. Chemical modifications e.g. the introduction of unnatural amino acids or cyclization, have been proven to be essential tools to overcome these limitations. This review article particularly focuses on available methods for the targeted chemical modification of peptides and peptide libraries in selected display approaches.

Inhibition of Listeria monocytogenes by the Staphylococcus capitis - derived bacteriocin capidermicin

Natural methods to control food pathogens are required and bacteriocins have received much interest in this regard. The aim of this study was to investigate the ability of the novel bacteriocin capidermicin to inhibit Listeria monocytogenes. Agar-based deferred antagonism assays were carried out with the capidermicin producer against 17 L. monocytogenes strains and large zones of inhibition were observed for 12 strains. Minimal inhibitory concentration assays performed with purified capidermicin peptide revealed MIC values between 680 nM and 11 μM. Biofilm assays were performed with five L. monocytogenes strains. Addition of capidermicin prevented biofilm formation by one strain and could remove pre-established biofilms of all five strains. Broth based growth experiments demonstrated that addition of capidermicin resulted in an extended lag phase of both L. monocytogenes strains tested. Kill-curve experiments showed that capidermicin was able to potentiate the anti-Listeria effects of the lantibiotic nisin. This enhanced killing by the combination of both peptides was also observed in model food systems (cottage cheese and chocolate milk). In summary, we show that capidermicin can inhibit L. monocytogenes and warrants further investigation as a potential natural agent for the control of this pathogen.

A Cell-Free Platform Based on Nisin Biosynthesis for Discovering Novel Lanthipeptides and Guiding their Overproduction In Vivo

Lanthipeptides have extensive therapeutic and industrial applications. However, because many are bactericidal, traditional in vivo platforms are limited in their capacity to discover and mass produce novel lanthipeptides as bacterial organisms are often critical components in these systems. Herein, the development of a cell-free protein synthesis (CFPS) platform that enables rapid genome mining, screening, and guided overproduction of lanthipeptides in vivo is described. For proof-of-concept studies, a type I lanthipeptide, nisin, is selected. Four novel lanthipeptides with antibacterial activity are identified among all nisin analogs in the National Center for Biotechnology Information (NCBI) database in a single day. Further, the CFPS platform is coupled with a screening assay for anti-gram-negative bacteria growth, resulting in the identification of a potent nisin mutant, M5. The titers of nisin and the nisin analog are found to be improved with CFPS platform guidance. Owing to the similarities in biosynthesis, the CFPS platform is broadly applicable to other lanthipeptides, thereby providing a universal method for lanthipeptide discovery and overproduction.

Identification and characterisation of capidermicin, a novel bacteriocin produced by Staphylococcus capitis

One hundred human-derived coagulase negative staphylococci (CoNS) were screened for antimicrobial activity using agar-based deferred antagonism assays with a range of indicator bacteria. Based on the findings of the screen and subsequent well assays with cell free supernatants and whole cell extracts, one strain, designated CIT060, was selected for further investigation. It was identified as Staphylococcus capitis and herein we describe the purification and characterisation of the novel bacteriocin that the strain produces. This bacteriocin which we have named capidermicin was extracted from the cell-free supernatant of S. capitis CIT060 and purified to homogeneity using reversed-phase high performance liquid chromatography (RP-HPLC). Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometric (MS) analysis revealed that the capidermicin peptide has a mass of 5,464 Da. Minimal inhibitory concentration (MIC) experiments showed that capidermicin was active in the micro-molar range against all the Gram-positive bacteria that were tested. Antimicrobial activity was retained over a range of pHs (2–11) and temperatures (10–121°C x 15 mins). The draft genome sequence of S. capitis CIT060 was determined and the genes predicted to be involved in the biosynthesis of capidermicin were identified. These genes included the predicted capidermicin precursor gene, and genes that are predicted to encode a membrane transporter, an immunity protein and a transcriptional regulator. Homology searches suggest that capidermicin is a novel member of the family of class II leaderless bacteriocins.

Lichenicidin rational site-directed mutagenesis library: A tool to generate bioengineered lantibiotics

Lantibiotics are ribosomally synthesized and posttranslationally modified antimicrobial peptides that arise as an alternative to the traditional antibiotics. Lichenicidin is active against clinically relevant bacteria and it was the first lantibiotic to be fully produced in vivo in the Gram-negative host Escherichia coli. Here, we present the results of a library of lichenicidin mutants, in which the mutations were generated based on the extensive bibliographical search available for other lantibiotics. The antibacterial activity of two-peptide lantibiotics, as is lichenicidin, requires the synergistic activity of two peptides. We established a method that allows screening for bioactivity which does not require the purification of the complementary peptide. It is an inexpensive, fast and user-friendly method that can be scaled up to screen large libraries of bioengineered two-peptide lantibiotics. The applied system is reliable and robust because, in general, the results obtained corroborate structure-activity relationship studies carried out for other lantibiotics.

Production of Bioactive Peptides from Lactic Acid Bacteria: A Sustainable Approach for Healthier Foods

Traditional fermented foods where lactic acid bacteria (LAB) are present have been associated with beneficial effects on human health, and some of those benefits are related to protein-derived products. Peptides produced by LAB have attracted the interest of food industries because of their diverse applications. These peptides include ribosomally produced (bacteriocins) and protein hydrolysates by-products (bioactive peptides), which can participate as natural preservatives and nutraceuticals, respectively. It is essential to understand the biochemical pathways and the effect of growth conditions for the production of bioactive peptides and bacteriocins by LAB, in order to suggest strategies for optimization. LAB is an important food-grade expression system that can be used in the simultaneous production of peptide-based products for the food, animal, cosmetic, and pharmaceutical industries. This review describes the multifunctional proteinaceous compounds generated by LAB metabolism and discusses a strategy to use a single-step production process, using an alternative protein-based media. This strategy will provide economic advantages in fermentation processes and will also provide an environmental alternative to industrial waste valorization. New technologies that can be used to improve production and bioactivity of LAB-derived peptides are also analyzed.

Comparison of the Potency of the Lipid II Targeting Antimicrobials Nisin, Lacticin 3147 and Vancomycin Against Gram-Positive Bacteria

While nisin (lantibiotic), lacticin 3147 (lantibiotic) and vancomycin (glycopeptides) are among the best studied lipid II-binding antimicrobials, their relative activities have never been compared. Nisin and lacticin 3147 have been employed/investigated primarily as food preservatives, although they do have potential in terms of veterinary and clinical applications. Vancomycin is used exclusively in clinical therapy. We reveal a higher potency for lacticin 3147 (MIC 0.95-3.8 μg/ml) and vancomycin (MIC 0.78-1.56 μg/ml) relative to that of nisin (MIC 6.28-25.14 μg/ml) against the food-borne pathogen Listeria monocytogenes. A comparison of the activity of the three antimicrobials against nisin resistance mutants of L. monocytogenes also reveals that their susceptibility to vancomycin and lacticin 3147 changed only slightly or not at all. A further assessment of relative activity against a selection of Bacillus cereus, Enterococcus and Staphylococcus aureus targets revealed that vancomycin MICs consistently ranged between 0.78 and 1.56 μg/ml against all but one strain. Lacticin 3147 was found to be more effective than nisin against B. cereus (lacticin 3147 MIC 1.9-3.8 μg/ml; nisin MIC 4.1-16.7 μg/ml) and E. faecium and E. faecalis targets (lacticin 3147 MIC from 1.9 to 3.8 μg/ml; nisin MIC ≥8.3 μg/ml). The greater effectiveness of lacticin 3147 is even more impressive when expressed as molar values. However, in agreement with the previous reports, nisin was the more effective of the two lantibiotics against S. aureus strains. This study highlights that in many instances the antimicrobial activity of these leading lantibiotics are comparable with that of vancomycin and emphasizes their particular value with respect to use in situations including foods and veterinary medicine, where the use of vancomycin is not permitted.

Bacteriocins and their position in the next wave of conventional antibiotics

Micro-organisms are capable of producing a range of defence mechanisms, including antibiotics, bacteriocins, lytic agents, protein exotoxins, etc. Such mechanisms have been identified in nearly 99% of studied bacteria. The multiplicity and diversity of bacteriocins and the resultant effects of their interactions with targeted bacteria on microbial ecology has been thoroughly studied and remains an area of investigation attracting many researchers. However, the incorporation of bacteriocins into drug delivery systems used in conjunction with, or as potential alternatives to, conventional antibiotics is only a recent, although rapidly expanding, field. The extensive array of bacteriocins positions them as one of the most promising options in the next wave of antibiotics. The goal of this review was to explore bacteriocins as novel antimicrobials, alone and in combination with established antibiotics, and thus position them as a potential tool for addressing the current antibiotic crisis.

The two peptide lantibiotic lacticin 3147 acts synergistically with polymyxin to inhibit Gram negative bacteria

BACKGROUND

The emergence of bacterial drug resistance encourages the re-evaluation of the potential of existing antimicrobials. Lantibiotics are post-translationally modified, ribosomally synthesised antimicrobial peptides with a broad spectrum antimicrobial activity. Here, we focussed on expanding the potential of lacticin 3147, one of the most studied lantibiotics and one which possesses potent activity against a wide range of Gram positive species including many nosocomial pathogens. More specifically, our aim was to investigate if lacticin 3147 activity could be enhanced when combined with a range of different clinical antibiotics.

RESULTS

Initial screening revealed that polymyxin B and polymyxin E (colistin) exhibited synergistic activity with lacticin 3147. Checkerboard assays were performed against a number of strains, including both Gram positive and Gram negative species. The resultant fractional inhibitory concentration (FIC) index values established that, while partial synergy was detected against Gram positive targets, synergy was obvious against Gram negative species, including Cronobacter and E. coli.

CONCLUSIONS

Combining lacticin 3147 with low levels of a polymyxin could provide a means of broadening target specificity of the lantibiotic, while also reducing polymyxin use due to the lower concentrations required as a result of synergy.

Strategies to improve the bacteriocin protection provided by lactic acid bacteria

Lactic acid bacteria (LAB) produce a wide variety of antimicrobial peptides (bacteriocins) which contribute to the safety and preservation of fermented foods. This review discusses strategies that have been or could be employed to further enhance the commercial application of bacteriocins and/or bacteriocin-producing LAB for food use.

Enhanced production of nukacin D13E in Lactococcus lactis NZ9000 by the additional expression of immunity genes

Nukacin D13E (D13E) is a variant of type-A(II) lantibiotic nukacin ISK-1 produced by Staphylococcus warneri ISK-1. D13E exhibited a twofold higher specific antimicrobial activity than nukacin ISK-1 against a number of Gram-positive bacteria. We previously reported the heterologous production of D13E in Lactococcus lactis NZ9000 under the control of nisin-controlled gene expression system. In this study, we demonstrated enhanced production of D13E by the additional expression of immunity genes, nukFEG. The nukacin ISK-1 immunity, conferred by the ABC transporter complex, NukFEG, and the lantibiotic-binding protein, NukH, was not overwhelmed by D13E. The additional NukFEG resulted in a fourfold increase in the immunity level of the strain and a 5.2-fold increase in D13E production. The additional NukFEGH-expressing strain with the highest D13E immunity showed reduced level of production. Further improvement in D13E production was achieved by using pH-controlled batch fermentation.

Discovery and development of lantibiotics; antimicrobial agents that have significant potential for medical application

INTRODUCTION

Antimicrobial drug resistance is driving the need for novel therapeutics. Amongst the most promising antibacterial agents that are being investigated as replacements for current therapeutic antibiotics are antibacterial peptides, such as the lanthionine-containing peptide antibiotics (lantibiotics).

AREAS COVERED

This review focuses on the current methods used for discovery of potentially exploitable lantibiotics for medical applications and discusses relevant recent innovations that will have a positive impact on the discovery of useful lantibiotics.

EXPERT OPINION

Recent technological advances in a number of fields mean that increased research into the identification and characterisation of new lantibiotics is feasible. We need to increase our understanding of the various mechanisms of antibacterial action exhibited by lantibiotics and apply this knowledge to peptide engineering or novel practical applications. The advent of next-generation sequencing approaches now negate the need for extensive reverse genetics and employment of bioinformatics approaches is greatly assisting the identification of potentially useful inhibitors in the genomes of a range of clinically significant bacteria. These advances in genetic analysis and engineering will facilitate increased exploitation of lantibiotics in medical therapy.

Studies with bioengineered Nisin peptides highlight the broad-spectrum potency of Nisin V

Nisin A is the most thoroughly investigated member of the lantibiotic family of antimicrobial peptides. In addition to a long history of safe use as a food antimicrobial, its activity against multi-drug resistant pathogens has resulted in a renewed interest in applying nisin as a chemotherapeutic to treat bacterial infections. The wealth of Nisin-related information that has been generated has also led to the development of the biotechnological capacity to engineer novel Nisin variants with a view to improving the function and physicochemical properties of this already potent peptide. However, the identification of bioengineered Nisin derivatives with enhanced antimicrobial activity against Gram-positive targets is a recent event. In this study, we created stable producers of the most promising derivatives of Nisin A generated to date [M21V (hereafter Nisin V) and K22T (hereafter Nisin T)] and assessed their potency against a range of drug-resistant clinical, veterinary and food pathogens. Nisin T exhibited increased activity against all veterinary isolates, including streptococci and staphylococci, and against a number of multi-drug resistant clinical isolates including MRSA, but not vancomycin-resistant enterococci. In contrast, Nisin V displayed increased potency against all targets tested including hVISA strains and the hyper-virulent Clostridium difficile ribotype 027 and against important food pathogens such as Listeria monocytogenes and Bacillus cereus. Significantly, this enhanced activity was validated in a model food system against L. monocytogenes. We conclude that Nisin V possesses significant potential as a novel preservative or chemotherapeutic compound.

A comparison of the activities of lacticin 3147 and nisin against drug-resistant Staphylococcus aureus and Enterococcus species

OBJECTIVES

Our goal was to compare the activities of lacticin 3147 and nisin, two of the most well characterized lantibiotics, against antibiotic-resistant staphylococci and enterococci.

METHODS

We determined the MICs of lacticin 3147 and nisin for 20 strains of methicillin-resistant Staphylococcus aureus (MRSA), 20 strains of vancomycin-resistant enterococci (VRE), 6 strains of S. aureus with intermediate resistance to vancomycin (VISA), 5 strains of heterogeneous vancomycin-intermediate S. aureus (hVISA) and 4 strains of S. aureus that are susceptible to methicillin.

RESULTS

Lacticin 3147 displayed potent activity against VRE with MIC values between 1.9 and 7.7 mg/L, and varying levels of activity against S. aureus strains (MRSA, 1.9-15.4 mg/L; laboratory strains, >or=15.4 mg/L; hVISA, 15.4-30.9 mg/L; VISA, >or=61.8 mg/L). Nisin was more active against the S. aureus strains in general (MRSA and laboratory strains, 0.5-4.1 mg/L; VISA and hVISA, 2 to >or=8.3 mg/L), but was less effective than lacticin 3147 against VRE (2 to >or=8.3 mg/L).

CONCLUSIONS

Nisin is more effective against S. aureus whereas lacticin 3147 possesses greater potency against VRE. The modifications responsible for the vancomycin-resistant phenotypes of hVISA and VISA strains also provide protection against the two lantibiotics.

Influence of Ca(2+) ions on the activity of lantibiotics containing a mersacidin-like lipid II binding motif

Mersacidin binds to lipid II and thus blocks the transglycosylation step of the cell wall biosynthesis. Binding of lipid II involves a special motif, the so-called mersacidin-lipid II binding motif, which is conserved in a major subgroup of lantibiotics. We analyzed the role of Ca(2+) ions in the mode of action of mersacidin and some related peptides containing a mersacidin-like lipid II binding motif. We found that the stimulating effect of Ca(2+) ions on the antimicrobial activity known for mersacidin also applies to plantaricin C and lacticin 3147. Ca(2+) ions appear to facilitate the interaction of the lantibiotics with the bacterial membrane and with lipid II rather than being an essential part of a peptide-lipid II complex. In the case of lacticin 481, both the interaction with lipid II and the antimicrobial activity were Ca(2+) independent.

Continuous nisin production with bioengineered Lactococcus lactis strains

Nisin production in continuous cultures of bioengineered Lactococcus lactis strains that incorporate additional immunity and regulation genes was studied. Highest nisin activities were observed at 0.2 h(-1) dilution rate and 12.5 g l(-1) fructose concentration for all strains. Recombinant strains were able to produce greater amounts of nisin at dilution rates below 0.3 h(-1) compared to the control strain. However, this significant difference disappeared at dilution rates of 0.4 and 0.5 h(-1). For the strains LL27, LAC338, LAC339, and LAC340, optimum conditions for nisin production were determined to be at 0.29, 0.26, 0.27, and 0.27 h(-1) dilution rates and 11.95, 12.01, 11.63, and 12.50 g l(-1) fructose concentrations, respectively. The highest nisin productivity, 496 IU ml(-1) h(-1), was achieved with LAC339. The results of this study suggest that low dilution rates stabilize the high specific nisin productivity of the bioengineered strains in continuous fermentation. Moreover, response surface methodology analysis showed that regulation genes yielded high nisin productivity at wide ranges of dilution rates and fructose concentrations.

Cross-immunity and immune mimicry as mechanisms of resistance to the lantibiotic lacticin 3147

Lantibiotics are antimicrobial peptides that possess great potential as clinical therapeutic agents. These peptides exhibit many beneficial traits and in many cases the emergence of resistance is extremely rare. In contrast, producers of lantibiotics synthesize dedicated immunity proteins to provide self-protection. These proteins have very specific activities and cross-immunity is rare. However, producers of two peptide lantibiotics, such as lacticin 3147, face the unusual challenge of exposure to two active peptides (alpha and beta). Here, in addition to establishing the contribution of LtnI and LtnFE to lacticin 3147 immunity, investigations were carried out to determine if production of a closely related lantibiotic (i.e. staphylococcin C55) or possession of LtnI/LtnFE homologues could provide protection. Here we establish that not only are staphylococcin C55 producers cross-immune to lacticin 3147, and therefore represent a natural repository of Staphylococcus aureus strains that are protected against lacticin 3147, but that functional immunity homologues are also produced by strains of Bacillus licheniformis and Enterococcus faecium. This result raises the spectre of resistance through immune mimicry, i.e. the emergence of lantibiotic-resistant strains from the environment resulting from the possession/acquisition of immunity gene homologues. These phenomena will have to be considered carefully when developing lantibiotics for clinical application.

Mechanistic dissection of the enzyme complexes involved in biosynthesis of lacticin 3147 and nisin

The thioether rings in the lantibiotics lacticin 3147 and nisin are posttranslationally introduced by dehydration of serines and threonines, followed by coupling of these dehydrated residues to cysteines. The prepeptides of the two-component lantibiotic lacticin 3147, LtnA1 and LtnA2, are dehydrated and cyclized by two corresponding bifunctional enzymes, LtnM1 and LtnM2, and are subsequently processed and exported via one bifunctional enzyme, LtnT. In the nisin synthetase complex, the enzymes NisB, NisC, NisT, and NisP dehydrate, cyclize, export, and process prenisin, respectively. Here, we demonstrate that the combination of LtnM2 and LtnT can modify, process, and transport peptides entirely different from LtnA2 and that LtnT can process and transport unmodified LtnA2 and unrelated peptides. Furthermore, we demonstrate a higher extent of NisB-mediated dehydration in the absence of thioether rings. Thioether rings apparently inhibited dehydration, which implies alternating actions of NisB and NisC. Furthermore, certain (but not all) NisC-cyclized peptides were exported with higher efficiency as a result of their conformation. Taken together, these data provide further insight into the applicability of Lactococcus lactis strains containing lantibiotic enzymes for the design and production of modified peptides.

Lantibiotics: peptides of diverse structure and function

The current need for antibiotics with novel target molecules has coincided with advances in technical approaches for the structural and functional analysis of the lantibiotics, which are ribosomally synthesized peptides produced by gram-positive bacteria. These peptides have antibiotic or morphogenetic activity and are structurally defined by the presence of unusual amino acids introduced by posttranslational modification. Lantibiotics are complex polycyclic molecules formed by the dehydration of select Ser and Thr residues and the intramolecular addition of Cys thiols to the resulting unsaturated amino acids to form lanthionine and methyllanthionine bridges, respectively. Importantly, the structural and functional diversity of the lantibiotics is much broader than previously imagined. Here we discuss this growing collection of molecules and introduce some recently discovered peptides, review advances in enzymology and protein engineering, and discuss the regulatory networks that govern the synthesis of the lantibiotics by the producing organisms.

A System for the Random Mutagenesis of the Two-Peptide Lantibiotic Lacticin 3147: Analysis of Mutants Producing Reduced Antibacterial Activities

Lantibiotics are antimicrobial peptides that contain several unusual amino acids resulting from a series of enzyme-mediated posttranslational modifications. As a consequence of being gene-encoded, the implementation of peptide bioengineering systems has the potential to yield lantibiotic variants with enhanced chemical and physical properties. Here we describe a functional two-plasmid expression system which has been developed to allow random mutagenesis of the two-component lantibiotic, lacticin 3147. One of these plasmids contains a randomly mutated version of the two structural genes, ltnA1 and ltnA2, and the associated promoter, Pbac, while the other encodes the remainder of the proteins required for the biosynthesis of, and immunity to, lacticin 3147. To test this system, a bank of approximately 1,500 mutant strains was generated and screened to identify mutations that have a detrimental impact on the bioactivity of lacticin 3147. This strategy established/confirmed the importance of specific residues in the structural peptides and their associated leaders and revealed that a number of alterations which mapped to the -10 or -35 regions of Pbac abolished promoter activity.

Insertional mutagenesis to generate lantibiotic resistance in Lactococcus lactis

While the potential emergence of food spoilage and pathogenic bacteria with resistance to lantibiotics is a concern, the creation of derivatives of starter cultures and adjuncts that can grow in the presence of these antimicrobials may have applications in food fermentations. Here a bank of Lactococcus lactis IL1403 mutants was created and screened, and a number of novel genetic loci involved in lantibiotic resistance were identified.

Identification of a novel two-peptide lantibiotic, Haloduracin, produced by the alkaliphileBacillus haloduransC-125

Complete genome sequencing of the alkaliphilic bacterium Bacillus halodurans C-125 revealed the presence of several genes homologous to those involved in the production of lantibiotic peptides. Additional bioinformatic analysis identified a total of eleven genes, spanning a 15 kbp region, potentially involved in the production, modification, immunity and transport of a two-peptide lantibiotic. Having established that strain C-125 exhibited antimicrobial activity against a wide range of Gram-positive bacteria, it was demonstrated through peptide purification, MS and site-directed mutagenesis that this activity was indeed attributable to the production of a lantibiotic encoded by these genes. This antimicrobial has been designated haloduracin and represents the first occasion wherein production of two-peptide lantibiotic has been associated with a Bacillus sp. It is also the first example of a lantibiotic of any kind to be produced by an alkaliphilic species.

Engineering dehydro amino acids and thioethers into peptides using lacticin 481 synthetase

Lantibiotics are peptide antimicrobials containing the thioether-bridged amino acids lanthionine (Lan) and methyllanthionine (MeLan) and often the dehydrated residues dehydroalanine (Dha) and dehydrobutyrine (Dhb). While biologically advantageous, the incorporation of these residues into peptides is synthetically daunting, and their production in vivo is limited to peptides containing proteinogenic amino acids. The lacticin 481 synthetase LctM offers versatile control over the installation of dehydro amino acids and thioether rings into peptides. In vitro processing of semisynthetic substrates unrelated to the prelacticin 481 peptide demonstrated the broad substrate tolerance of LctM. Furthermore, a chemoenzymatic strategy was employed to generate novel thioether linkages by cyclization of peptidic substrates containing the nonproteinogenic cysteine analogs homocysteine and beta-homocysteine. These findings are promising with respect to the utility of LctM toward preparation of conformationally constrained peptide therapeutics.