Development of bacteriocinogenic strains of Saccharomyces cerevisiae heterologously expressing and secreting the leaderless enterocin L50 peptides L50A and L50B from Enterococcus faecium L50

Heterologous Expression of Plantaricin 423 and Mundticin ST4SA in Saccharomyces cerevisiae

Antimicrobial peptides or bacteriocins are excellent candidates for alternative antimicrobials, but high manufacturing costs limit their applications. Recombinant gene expression offers the potential to produce these peptides more cost-effectively at a larger scale. Saccharomyces cerevisiae is a popular host for recombinant protein production, but with limited success reported on antimicrobial peptides. Individual recombinant S. cerevisiae strains were constructed to secrete two class IIa bacteriocins, plantaricin 423 (PlaX) and mundticin ST4SA (MunX). The native and codon-optimised variants of the plaA and munST4SA genes were cloned into episomal expression vectors containing either the S. cerevisiae alpha mating factor (MFα1) or the Trichoderma reesei xylanase 2 (XYNSEC) secretion signal sequences. The recombinant peptides retained their activity and stability, with the MFα1 secretion signal superior to the XYNSEC secretion signal for both bacteriocins. An eight-fold increase in activity against Listeria monocytogenes was observed for MunX after codon optimisation, but not for PlaX-producing strains. After HPLC-purification, the codon-optimised genes yielded 20.9 mg/L of MunX and 18.4 mg/L of PlaX, which displayed minimum inhibitory concentrations (MICs) of 108.52 nM and 1.18 µM, respectively, against L. monocytogenes. The yields represent a marked improvement relative to an Escherichia coli expression system previously reported for PlaX and MunX. The results demonstrated that S. cerevisiae is a promising host for recombinant bacteriocin production that requires a simple purification process, but the efficacy is sensitive to codon usage and secretion signals.

Strategies for improving antimicrobial peptide production

Antimicrobial peptides (AMPs) found in a wide range of animal, insect, and plant species are host defense peptides forming an integral part of their innate immunity. Although the exact mode of action of some AMPs is yet to be deciphered, many exhibit membrane lytic activity or interact with intracellular targets. The ever-growing threat of antibiotic resistance has brought attention to research on AMPs to enhance their clinical use as a therapeutic alternative. AMPs have several advantages over antibiotics such as broad range of antimicrobial activities including anti-fungal, anti-viral and anti-bacterial, and have not reported to contribute to resistance development. Despite the numerous studies to develop efficient production methods for AMPs, limitations including low yield, degradation, and loss of activity persists in many recombinant approaches. In this review, we outline available approaches for AMP production and various expression systems used to achieve higher yield and quality. In addition, recent advances in recombinant strategies, suitable fusion protein partners, and other molecular engineering strategies for improved AMP production are surveyed.

Antibacterial Activity of Pediocin and Pediocin-Producing Bacteria Against Listeria monocytogenes in Meat Products

One of the most important challenges in the food industry is to produce healthy and safe food products, and this could be achieved through various processes as well as the use of different additives, especially chemical preservatives. However, consumer awareness and concern about chemical preservatives have led researchers to focus on the use of natural antimicrobial compounds such as bacteriocins. Pediocins, which belong to subclass IIa of bacteriocin characterized as small unmodified peptides with a low molecular weight (2.7-17 kDa), are produced by some of the Pediococcus bacteria. Pediocin and pediocin-like bacteriocins exert a broad spectrum of antimicrobial activity against Gram-positive bacteria, especially against pathogenic bacteria, such as Listeria monocytogenes through formation of pores in the cytoplasmic membrane and cell membrane dysfunction. Pediocins are sensitive to most protease enzymes such as papain, pepsin, and trypsin; however, they keep their antimicrobial activity during heat treatment, at low temperatures even at -80°C, and after treatment with lipase, lysozyme, phospholipase C, DNase, or RNase. Due to the anti-listeria activity of pediocin on the one hand and the potential health hazards associated with consumption of meat products on the other hand, this review aimed to investigate the possible application of pediocin in preservation of meat and meat products against L. monocytogenes.

Construction of Leaderless-Bacteriocin-Producing Bacteriophage Targeting E. coli and Neighboring Gram-Positive Pathogens

Lytic bacteriophages are expected as effective tools to control infectious bacteria in human and pathogenic or spoilage bacteria in foods. Leaderless bacteriocins (LLBs) are simple bacteriocins produced by Gram-positive bacteria. LLBs do not possess an N-terminal leader peptide in the precursor, which means that they are active immediately after translation. In this study, we constructed a novel antimicrobial agent, an LLB-producing phage (LLB-phage), by genetic engineering to introduce the LLB structural gene into the lytic phage genome. To this end, lnqQ (structure gene of an LLB, lacticin Q) and trxA, an essential gene for T7 phage genome replication, were integrated in tandem into T7 phage genome using homologous recombination in Escherichia coli host strain. The recombinant lnqQ-T7 phage was isolated by a screening method using ΔtrxA host strain. lnqQ-T7 phage formed a clear halo in agar plates containing both E. coli and lacticin Q-susceptible Bacillus coagulans, indicating that lnqQ-T7 phage could produce a significant amount of lacticin Q. Lacticin Q production did not exert a significant effect on the lytic cycle of T7 phage. In fact, the production of lacticin Q enhanced T7 phage lytic activity and helped to prevent the emergence of bacterial populations resistant against this phage. These results serve as a proof of principle for LLB-phages. There are different types of LLBs and phages, meaning that in the future, it may be possible to produce any number of LLB-phages which can be designed to efficiently control different types of bacterial contamination in different settings.

IMPORTANCE We demonstrated that we could combine LLB and phage to construct promising novel antimicrobial agents, LLB-phage. The first LLB-phage, lnqQ-T7 phage, can control the growth of both the Gram-negative host strain and neighboring Gram-positive bacteria while preventing the emergence of phage resistance in the host strain. There are several different types of LLBs and phages, suggesting that we may be able to design a battery of LLB-phages by selecting novel combinations of LLBs and phages. These constructs could be tailored to control various bacterial contaminations and infectious diseases.

A Leaderless Two-Peptide Bacteriocin, Enterocin DD14, Is Involved in Its Own Self-Immunity: Evidence and Insights

Enterocin DD14 (EntDD14) is a two-peptide leaderless bacteriocin produced by Enterococcus faecalis 14, a strain previously isolated from meconium. EntDD14 has a strong antibacterial activity against Gram-positive bacteria. Leaderless bacteriocins, unlike bacteriocins with leader peptides, are immediately active after their translation, and a producing strain has then to develop specific mechanisms to protect both intra and extracellular compartments. The in silico analysis of Ent. faecalis 14 genome allowed to locate downstream of structural ddAB genes, 8 other adjacent genes, designed ddCDEFGHIJ, which collectively may form three operons. To gain insights on immunity mechanisms of Ent. faecalis 14, mutant strains knocked out in ddAB genes encoding bacteriocin precursor peptides (Δbac) and/or ABC transporter (ΔddI) of EntDD14 were constructed and characterized. Importantly, Δbac mutant strains, from which structural ddAB genes were deleted, resulted unable to produce EntDD14 and sensitive to exogenous EntDD14 showing their involvement in the Ent. faecalis 14 immunity system. Moreover, the sensitivity of Δbac mutants appeared not to be associated with the down-regulation of ddCDEFGHIJ gene expression since they were similarly expressed in both Δbac and wild-type strains during the log phase while they were found significantly down-regulated in the Δbac mutant strain after 24 h of growth. Data gathered from this study suggest also the implication of the ABC transporter (ddHIJ) in the active export of EntDD14 but ruled-out its involvement in the primary self-immunity system. Interestingly, non-bacteriocin producing Ent. faecalis JH2-2 cells transformed with ddAB, or ddAB plus genes encoding the ABC transporter (ddAB-HIJ) did not produce EntDD14 and remained sensitive to its action. Of note, trans-complementation of the Δbac mutant strain with these constructions allowed to recover the WT phenotype. To the best of our knowledge, this is the first study delineating the role of the intracellular two-peptide leaderless bacteriocins in their self-immunity.

Strategies for recombinant production of antimicrobial peptides with pharmacological potential

INTRODUCTION

The need to develop new drugs for the control of pathogenic microorganisms has redoubled efforts to prospect for antimicrobial peptides (AMPs) from natural sources and to characterize its structure and function. These molecules present a broad spectrum of action against different microorganisms and frequently present promiscuous action, with anticancer and immunomodulatory activities. Furthermore, AMPs can be used as biopharmaceuticals in the treatment of hospital-acquired infections and other serious diseases with relevant social and economic impacts.Areas covered: The low yield and the therefore difficult extraction and purification process in AMPs are problems that limit their industrial application and scientific research. Thus, optimized heterologous expression systems were developed to significantly boost AMP yields, allow high efficiency in purification and structural optimization for the increase of therapeutic activity.Expert opinion: This review provides an update on recent developments in the recombinant production of ribosomal and non-ribosomal synthesis of AMPs and on strategies to increase the expression of genes encoding AMPs at the transcriptional and translational levels and regulation of the post-translational modifications. Moreover, there are detailed reports of AMPs that have already reached marketable status or are in the pipeline under advanced stages of preclinical testing.

Circular and Leaderless Bacteriocins: Biosynthesis, Mode of Action, Applications, and Prospects

Bacteriocins are a huge family of ribosomally synthesized peptides known to exhibit a range of bioactivities, most predominantly antibacterial activities. Bacteriocins from lactic acid bacteria are of particular interest due to the latter's association to food fermentation and the general notion of them to be safe. Among the family of bacteriocins, the groups known as circular bacteriocins and leaderless bacteriocins are gaining more attention due to their enormous potential for industrial application. Circular bacteriocins and leaderless bacteriocins, arguably the least understood groups of bacteriocins, possess distinctively peculiar characteristics in their structures and biosynthetic mechanisms. Circular bacteriocins have N-to-C- terminal covalent linkage forming a structurally distinct circular peptide backbone. The circular nature of their structures provides them superior stability against various stresses compared to most linear bacteriocins. The molecular mechanism of their biosynthesis, albeit has remained poorly understood, is believed to possesses huge application prospect as it can serve as scaffold in bioengineering other biologically important peptides. On the other hand, while most bacteriocins are synthesized as inactive precursor peptides, which possess an N-terminal leader peptide attached to a C-terminal propeptide, leaderless bacteriocins are atypical as they do not have an N-terminal leader peptide, hence the name. Leaderless bacteriocins are active right after translation as they do not undergo any post-translational processing common to other groups of bacteriocins. This "simplicity" in the biosynthesis of leaderless bacteriocins offers a huge commercial potential as scale-up production systems are considerably easier to assemble. In this review, we summarize the current studies of both circular and leaderless bacteriocins, highlighting the progress in understanding their biosynthesis, mode of action, application and their prospects.

High-level heterologous production and Functional Secretion by recombinant Pichia pastoris of the shortest proline-rich antibacterial honeybee peptide Apidaecin

Drug resistance is a major problem in antibacterial chemotherapy. Apidaecins, which refer to a series of small, proline-rich antimicrobial peptides, are predominantly active against many drug-resistant bacteria. The apidaecins have special antibacterial mechanisms, and are non-toxic for human cells, a prerequisite for using them as novel antibiotic drugs. However, no efficient non-tagged apidaecin expression system has been reported, which is the limiting factor for their application. Here we successfully generated a Pichia pastoris transformant expressing and secreting apidaecin. However, expression was unstable and poor. Analysis of this revealed that the integration plasmid was frequently lost and that apidaecin expression resulted in cell death. Using N-methyl-N-nitro-N-nitroso-guanidine mutagenesis and selection, a mutant strain Apmu4 was derived, in which the rate of loss of the integration plasmid was much lower after induction, and which produced improved titres of apidaecin. Additionally, we discovered that using glucose as the sole carbon source to pre-culture the strain before induction could greatly enhance apidaecin production. A pilot-scale 10 L fermentation yielded 418 mg/L of recombinant apidaecin, which represents the highest reported yield of apidaecin. Consequently, this study reports the first super heterologous expression and secretion of apidaecin in yeast.

Controlled functional expression of the bacteriocins pediocin PA-1 and bactofencin A in Escherichia coli

The bacteriocins bactofencin A (class IId) and pediocin PA-1 (class IIa) are encoded by operons with a similarly clustered gene organization including a structural peptide, an immunity protein, an ABC transporter and accessory bacteriocin transporter protein. Cloning of these operons in E. coli Tuner^TM (DE3) on a pETcoco-2 derived vector resulted in successful secretion of both bacteriocins. A corresponding approach, involving the construction of vectors containing different combinations of these genes, revealed that the structural and the transporter genes alone are sufficient to permit heterologous production and secretion in this host. Even though the accessory protein, usually associated with optimal disulfide bond formation, was not required for bacteriocin synthesis, its presence did result in greater pediocin PA-1 production. The simplicity of the system and the fact that the associated bacteriocins could be recovered from the extracellular medium provides an opportunity to facilitate protein engineering and the overproduction of biologically-active bacteriocins at industrial scale. Additionally, this system could enable the characterization of new bacteriocin operons where genetic tools are not available for the native producers.

Nisin Z Production by Lactococcus lactis subsp. cremoris WA2-67 of Aquatic Origin as a Defense Mechanism to Protect Rainbow Trout (Oncorhynchus mykiss, Walbaum) Against Lactococcus garvieae

Probiotics represent an alternative to chemotherapy and vaccination to control fish diseases, including lactococcosis caused by Lactococcus garvieae. The aims of this study were (i) to determine the in vitro probiotic properties of three bacteriocinogenic Lactococcus lactis subsp. cremoris of aquatic origin, (ii) to evaluate in vivo the ability of L. cremoris WA2-67 to protect rainbow trout (Oncorhynchus mykiss, Walbaum) against infection by L. garvieae, and (iii) to demonstrate the role of nisin Z (NisZ) production as an anti-infective mechanism. The three L. cremoris strains survived in freshwater at 18 °C for 7 days, withstood exposure to pH 3.0 and 10 % (v/v) rainbow trout bile, and showed different cell surface hydrophobicity (37.93-58.52 %). The wild-type NisZ-producer L. cremoris WA2-67 and its non-bacteriocinogenic mutant L. cremoris WA2-67 ∆nisZ were administered orally (10(6) CFU/g) to rainbow trout for 21 days and, subsequently, fish were challenged with L. garvieae CLG4 by the cohabitation method. The fish fed with the bacteriocinogenic strain L. cremoris WA2-67 reduced significantly (p < 0.01) the mortality (20 %) compared to the fish treated with its non-bacteriocinogenic knockout isogenic mutant (50 %) and the control (72.5 %). We demonstrated the effectiveness of L. cremoris WA2-67 to protect rainbow trout against infection with the invasive pathogen L. garvieae and the relevance of NisZ production as an anti-infective mechanism. This is the first report demonstrating the effective in vivo role of LAB bacteriocin (NisZ) production as a mechanism to protect fish against bacterial infection. Our results suggest that the wild-type NisZ-producer strain L. cremoris WA2-67 could be used in fish farming to prevent lactococcosis in rainbow trout.

Use of synthetic genes for cloning, production and functional expression of the bacteriocins enterocin A and bacteriocin E 50-52 by Pichia pastoris and Kluyveromyces lactis

The use of synthetic genes may constitute a successful approach for the heterologous production and functional expression of bacterial antimicrobial peptides (bacteriocins) by recombinant yeasts. In this work, synthetic genes with adapted codon usage designed from the mature amino acid sequence of the bacteriocin enterocin A (EntA), produced by Enterococcus faecium T136, and the mature bacteriocin E 50-52 (BacE50-52), produced by E. faecium NRRL B-32746, were synthesized. The synthetic entA and bacE50-52 were cloned into the protein expression vectors pPICZαA and pKLAC2 for transformation of derived vectors into Pichia pastoris X-33 and Kluyveromyces lactis GG799, respectively. The recombinant vectors were linearized and transformed into competent cells selecting for P. pastoris X-33EAS (entA), P. pastoris X-33BE50-52S (bacE50-52), K. lactis GG799EAS (entA), and K. lactis GG799BE50-52S (bacE50-52). P. pastoris X-33EAS and K. lactis GG799EAS, but not P. pastoris X-33BE50-52S and K. lactis GG799BE50-52S, showed antimicrobial activity in their supernatants. However, purification of the supernatants of the producer yeasts permitted recovery of the bacteriocins EntA and BacE50-52. Both purified bacteriocins were active against Gram-positive bacteria such as Listeria monocytogenes but not against Gram-negative bacteria, including Campylobacter jejuni.

Derivatives of the antimicrobial peptide BP100 for expression in plant systems

Production of antimicrobial peptides in plants constitutes an approach for obtaining them in high amounts. However, their heterologous expression in a practical and efficient manner demands some structural requirements such as a minimum size, the incorporation of retention signals to assure their accumulation in specific tissues, and the presence of protease cleavage amino acids and of target sequences to facilitate peptide detection. Since any sequence modification may influence the biological activity, peptides that will be obtained from the expression must be screened prior to the synthesis of the genes for plant transformation. We report herein a strategy for the modification of the antimicrobial undecapeptide BP100 that allowed the identification of analogues that can be expressed in plants and exhibit optimum biological properties. We prepared 40 analogues obtained by incorporating repeated units of the antimicrobial undecapeptide, fragments of natural peptides, one or two AGPA hinges, a Gly or Ser residue at the N-terminus, and a KDEL fragment and/or the epitope tag54 at the C-terminus. Their antimicrobial, hemolytic and phytotoxic activities, and protease susceptibility were evaluated. Best sequences contained a magainin fragment linked to the antimicrobial undecapeptide through an AGPA hinge. Moreover, since the presence of a KDEL unit or of tag54 did not influence significantly the biological activity, these moieties can be introduced when designing compounds to be retained in the endoplasmic reticulum and detected using a complementary epitope. These findings may contribute to the design of peptides to be expressed in plants.

Cloning, production, and functional expression of the bacteriocin sakacin A (SakA) and two SakA-derived chimeras in lactic acid bacteria (LAB) and the yeasts Pichia pastoris and Kluyveromyces lactis

Mature sakacin A (SakA, encoded by sapA) and its cognate immunity protein (SakI, encoded by sapiA), and two SakA-derived chimeras mimicking the N-terminal end of mature enterocin P (EntP/SakA) and mature enterocin A (EntA/SakA) together with SakI, were fused to different signal peptides (SP) and cloned into the protein expression vectors pNZ8048 and pMG36c for evaluation of their production and functional expression by different lactic acid bacteria. The amount, antimicrobial activity, and specific antimicrobial activity of SakA and its chimeras produced by Lactococcus lactis subsp. cremoris NZ9000 depended on the SP and the expression vector. Only L. lactis NZ9000 (pNUPS), producing EntP/SakA, showed higher bacteriocin production and antimicrobial activity than the natural SakA-producer Lactobacillus sakei Lb706. The lower antimicrobial activity of the SakA-producer L. lactis NZ9000 (pNUS) and that of the EntA/SakA-producer L. lactis NZ9000 (pNUAS) could be ascribed to secretion of truncated bacteriocins. On the other hand, of the Lb. sakei Lb706 cultures transformed with the pMG36c-derived vectors only Lb. sakei Lb706 (pGUS) overproducing SakA showed a higher antimicrobial activity than Lb. sakei Lb706. Finally, cloning of SakA and EntP/SakA into pPICZαA and pKLAC2 permitted the production of SakA and EntP/SakA by recombinant Pichia pastoris X-33 and Kluyveromyces lactis GG799 derivatives although their antimicrobial activity was lower than expected from their production.

New type non-lantibiotic bacteriocins: circular and leaderless bacteriocins

Bacteriocins are antimicrobial peptides that are ribosomally synthesised by bacteria. Bacteriocins produced by Gram-positive bacteria, including lactic acid bacteria, are under focus as the next generation of safe natural biopreservatives and as therapeutic alternatives to antibiotics. Recently, two novel types of non-lantibiotic class II bacteriocins have been reported with unique characteristics in their structure and biosynthesis mechanism. One is a circular bacteriocin that contains a head-to-tail structure in the mature form, and the other is a leaderless bacteriocin without an N-terminal extension in the precursor peptide. A circular structure can provide the peptide with remarkable stability against various stresses; indeed, circular bacteriocins are known to possess higher stability than general linear bacteriocins. Leaderless bacteriocins are distinct from general bacteriocins, because they do not contain N-terminal leader sequences, which are responsible for the recognition process during secretion and for inactivation of bacteriocins inside producer cells. Leaderless bacteriocins do not require any post-translational processing for activity. These two novel types of bacteriocins are promising antimicrobial compounds, and their biosynthetic mechanisms are expected to be applied in synthetic biology to design new peptides and for new mass production systems. However, many questions remain about their biosynthesis. In this review, we introduce recent studies on these types of bacteriocins and their potential to open a new world of antimicrobial peptides.

Cloning, production, and functional expression of the bacteriocin enterocin A, produced by Enterococcus faecium T136, by the yeasts Pichia pastoris, Kluyveromyces lactis, Hansenula polymorpha, and Arxula adeninivorans

The bacteriocin enterocin A (EntA) produced by Enterococcus faecium T136 has been successfully cloned and produced by the yeasts Pichia pastoris X-33EA, Kluyveromyces lactis GG799EA, Hansenula polymorpha KL8-1EA, and Arxula adeninivorans G1212EA. Moreover, P. pastoris X-33EA and K. lactis GG799EA produced EntA in larger amounts and with higher antimicrobial and specific antimicrobial activities than the EntA produced by E. faecium T136.

Use of the yeast Pichia pastoris as an expression host for secretion of enterocin L50, a leaderless two-peptide (L50A and L50B) bacteriocin from Enterococcus faecium L50

In this work, we report the expression and secretion of the leaderless two-peptide (EntL50A and EntL50B) bacteriocin enterocin L50 from Enterococcus faecium L50 by the methylotrophic yeast Pichia pastoris X-33. The bacteriocin structural genes entL50A and entL50B were fused to the Saccharomyces cerevisiae gene region encoding the mating pheromone alpha-factor 1 secretion signal (MFalpha1(s)) and cloned, separately and together (entL50AB), into the P. pastoris expression and secretion vector pPICZalphaA, which contains the methanol-inducible alcohol oxidase promoter (P(AOX1)) to express the fusion genes. After transfer into the yeast, the recombinant plasmids were integrated into the genome, resulting in three bacteriocinogenic yeast strains able to produce and secrete the individual bacteriocin peptides EntL50A and EntL50B separately and together. The secretion was efficiently directed by MFalpha1(s) through the Sec system, and the precursor peptides were found to be correctly processed to form mature and active bacteriocin peptides. The present work describes for the first time the heterologous expression and secretion of a two-peptide non-pediocin-like bacteriocin by a yeast.