Nisin-relevant antimicrobial peptides: synthesis strategies and applications.

Small pentacyclic peptides, represented by nisin, have been successfully utilized as preservatives in the food industry and have evolved into a paradigm for understanding the genetic structure, expression, and control of genes created by lantibiotics. Due to the ever-increasing antibiotic resistance, nisin-relevant antimicrobial peptides have received much attention, which calls for a summarization of their synthesis, modification and applications. In this review, we first provided a timeline of select highlights in nisin biosynthesis and engineering. Then, we outlined the current developments in nisin synthesis. We also provided an overview of the engineering, screening, and production of nisin-relevant antimicrobial peptides based on enzyme alteration, substrate modification, and sequence mining. Furthermore, an updated summary of applications of nisin-relevant antimicrobial peptides has been developed for food applications. Finally, this study offers insights into emerging technologies, limitations and the future development of nisin-relevant antimicrobial peptides for pathogen inhibition, food preservatives, and improved health.

AcrR1, a novel TetR/AcrR family repressor, mediates acid and antibiotic resistance and nisin biosynthesis in Lactococcus lactis F44.

Lactococcus lactis, widely used in the manufacture of dairy products, encounters various environmental stresses both in natural habitats and during industrial processes. It has evolved intricate machinery of stress sensing and defense to survive harsh stress conditions. Here, we identified a novel TetR/AcrR family transcription regulator, designated AcrR1, to be a repressor for acid and antibiotic tolerance that was derepressed in the presence of vancomycin or under acid stress. The survival rates of acrR1 deletion strain ΔAcrR1 under acid and vancomycin stresses were about 28.7-fold (pH 3.0, HCl), 8.57-fold (pH 4.0, lactic acid) and 2.73-fold (300 ng/mL vancomycin) greater than that of original strain F44. We also demonstrated that ΔAcrR1 was better able to maintain intracellular pH homeostasis and had a lower affinity to vancomycin. No evident effects of AcrR1 deletion on the growth and morphology of strain F44 were observed. Subsequently, we characterized that the transcription level of genes associated with amino acids biosynthesis, carbohydrate transport and metabolism, multidrug resistance, and DNA repair proteins significantly upregulated in ΔAcrR1 using transcriptome analysis and quantitative reverse transcription-PCR assays. Additionally, AcrR1 could repress the transcription of the nisin post-translational modification gene, nisC, leading to a 16.3% increase in nisin yield after AcrR1 deletion. Our results not only refined the knowledge of the regulatory mechanism of TetR/AcrR family regulator in L. lactis, but presented a potential strategy to enhance industrial production of nisin.

Recombinant production of the lantibiotic nisin using Corynebacterium glutamicum in a two-step process.

BACKGROUND: The bacteriocin nisin is naturally produced by Lactococcus lactis as an inactive prepeptide that is modified posttranslationally resulting in five (methyl-)lanthionine rings characteristic for class Ia bacteriocins. Export and proteolytic cleavage of the leader peptide results in release of active nisin. By targeting the universal peptidoglycan precursor lipid II, nisin has a broad target spectrum including important human pathogens such as Listeria monocytogenes and methicillin-resistant Staphylococcus aureus strains. Industrial nisin production is currently performed using natural producer strains resulting in rather low product purity and limiting its application to preservation of dairy food products. RESULTS: We established heterologous nisin production using the biotechnological workhorse organism Corynebacterium glutamicum in a two-step process. We demonstrate successful biosynthesis and export of fully modified prenisin and its activation to mature nisin by a purified, soluble variant of the nisin protease NisP (sNisP) produced in Escherichia coli. Active nisin was detected by a L. lactis sensor strain with strictly nisin-dependent expression of the fluorescent protein mCherry. Following activation by sNisP, supernatants of the recombinant C. glutamicum producer strain cultivated in standard batch fermentations contained at least 1.25 mg/l active nisin. CONCLUSIONS: We demonstrate successful implementation of a two-step process for recombinant production of active nisin with C. glutamicum. This extends the spectrum of bioactive compounds that may be produced using C. glutamicum to a bacteriocin harboring complex posttranslational modifications. Our results provide a basis for further studies to optimize product yields, transfer production to sustainable substrates and purification of pharmaceutical grade nisin.

Isolation and Analysis of the Nisin Biosynthesis Complex NisBTC: further Insights into Their Cooperative Action.

Nisin is synthesized by a putative membrane-associated lantibiotic synthetase complex composed of the dehydratase NisB, the cyclase NisC, and the ABC transporter NisT in Lactococcus lactis. Earlier work has demonstrated that NisB and NisT are linked via NisC to form such a complex. Here, we conducted for the first time the isolation of the intact NisBTC complex and NisT-associated subcomplexes from the cytoplasmic membrane by affinity purification. A specific interaction of NisT, not only with NisC but also with NisB, was detected. The cellular presence of NisB and/or NisC in complex with precursor nisin (NisA) was determined, which shows a highly dynamic and transient assembly of the NisABC complex via an alternating binding mechanism during nisin dehydration and cyclization. Mutational analyses, with cysteine-to-alanine mutations in NisA, suggest a tendency for NisA to lose affinity to NisC concomitant with an increasing number of completed lanthionine rings. Split NisBs were able to catalyze glutamylation and elimination reactions in an alternating way as efficiently as full-length NisB, with no significant influence on the following cyclization and transport. Notably, the harvest of the leader peptide in complex with the independent elimination domain of NisB points to a second leader peptide binding motif that is located in the C-terminal region of NisB, giving rise to a model where the leader peptide binds to different sites in NisB for glutamylation and elimination. Overall, these combined studies provide new insights into the cooperative biosynthesis mechanism of nisin and thereby lay a foundation for further structural and functional characterization of the NisBTC complex. IMPORTANCE Lantibiotics are ribosomally synthesized and posttranslationally modified peptide antibiotics. Although the membrane-associated lantibiotic biosynthesis machinery has long been proposed to exist, the isolation of such a complex has not been reported yet, which limits the elucidation of the processive mechanism of lantibiotic biosynthesis. In this work, we present direct evidence for the existence of the nisin biosynthetic complex at the cytoplasmic membrane of L. lactis, producing fully modified precursor nisin. By analyses of the interactions within the intact NisBTC complex and the modification machinery NisABC, we were able to elucidate the cooperative action for the modification and transport of nisin. Inspired by the natural and documented degradation process of NisB, artificial split-NisBs were made and thoroughly characterized, demonstrating a crucial clue to the evolution of the LanB family. Importantly, our study also suggests that the leader peptide of NisA binds to two different recognition motifs, i.e., one for glutamylation and one for elimination.

Adaptive Evolution of Lactococcus Lactis to Thermal and Oxidative Stress Increases Biomass and Nisin Production.

High values of agitation and temperature lead to stressful conditions in the fermentations of Lactococcus lactis due to its aero-tolerant and mesophilic nature. Here, the adaptive laboratory evolution (ALE) technique was applied to increase biomass and nisin production yields by enhancing L. lactis subsp. lactis robustness at higher growth temperature and aeration rates. In two separate ALE experiments, after 162 serial transfers, optimum agitation and growth temperature of L. lactis were shifted from 40 rpm and 30 °C to 200 rpm and 37 °C, respectively. Oxidative and acid resistance were enhanced in the evolved strain. Whole-genome sequencing revealed the emergence of five single-nucleotide polymorphisms in the genome of the evolved strain in jag, DnaB, ArgR, cation transporter genes, and one putative protein. The evolved strain of L. lactis in this study has more industrial desirable features and improved nisin production capability and can act more efficiently in nisin production in stressful conditions.

Visualization and Analysis of the Dynamic Assembly of a Heterologous Lantibiotic Biosynthesis Complex in Bacillus subtilis.

A membrane-associated lanthipeptide synthetase complex, consisting of the dehydratase NisB, the cyclase NisC, and the ABC transporter NisT, has been described for nisin biosynthesis in the coccoid bacterium Lactococcus lactis. Here, we used advanced fluorescence microscopy to visualize the functional nisin biosynthesis machinery in rod-shaped cells and analyzed its spatial distribution and dynamics employing a platform we developed for heterologous production of nisin in Bacillus subtilis. We observed that NisT, as well as NisB and NisC, were all distributed in a punctate pattern along the cell periphery, opposed to the situation in coccoid cells. NisBTC proteins were found to be highly colocalized, being visualized at the same spots by dual fluorescence microscopy. In conjunction with the successful isolation of the biosynthetic complex NisBTC from the cell membrane, this corroborated that the visual bright foci were the sites for nisin maturation and transportation. A strategy of differential timing of expression was employed to demonstrate the in vivo dynamic assembly of NisBTC, revealing the recruitment by NisT of NisBC to the membrane. Additionally, by use of mutated proteins, the nucleotide binding domain (NBD) of NisT was found to function as a membrane anchor for NisB and/or NisC. We also show that the nisin biosynthesis sites are static and likely associated with proteins residing in lipid rafts. Based on these data, we propose a model for a three-phase production of modified precursor nisin in rod-shaped bacteria, presenting the assembly dynamics of NisBTC and emphasizing the crucial role of NisBC, next to NisT, in the process of precursor nisin translocation. IMPORTANCE Nisin is a model antimicrobial peptide for LanBC-modified lantibiotics that are modified and transported by a membrane synthetase complex. Although the subcellular localization and the assembly process of such a complex in L. lactis have been described in our recent work (J. Chen, A. J. van Heel, and O. P. Kuipers, mBio 11:e02825-20, 2020, https://doi.org/10.1128/mBio.02825-20), it proved difficult to gain a more detailed insight into the exact LanBTC assembly in the L. lactis system. Rod-shaped cells, especially B. subtilis, are better suited to study the assembly dynamics of these protein complexes. In this work, we present evidence for the existence of the lanthipeptide biosynthetic complex by visualizing and isolating the machinery in vivo. The dynamic behavior of the modification machinery and the transporter within the cells was characterized in depth, revealing the dependence of first LanB and LanC on each other and subsequent recruitment of them by LanT during the machinery assembly. Importantly, the elucidation of the dynamic assembly of the complex will facilitate future studies of lanthipeptide transport mechanisms and the structural characterization of the complete complex.

Efficient Production of Nisin A from Low-Value Dairy Side Streams Using a Nonengineered Dairy Lactococcus lactis Strain with Low Lactate Dehydrogenase Activity.

Nisin is commonly used as a biopreservative in foods. For industrial production, nisin-producing Lactococcus lactis strains are usually grown to high cell densities to achieve the highest possible nisin titer. However, accumulation of lactic acid eventually halts production, even in pH-controlled fermentations. Here, we describe a nisin-producing L. lactis strain Ge001, which was obtained after transferring the nisin gene cluster from L. lactis ATCC 11454, by conjugation, into the natural mutant L. lactis RD1M5, with low lactate dehydrogenase activity. The ability of Ge001 to produce nisin was tested using dairy waste as the fermentation substrate. To accommodate redox cofactor regeneration, respiration conditions were used, and to alleviate oxidative stress and to reduce adsorption of nisin onto the producing cells, we found it to be beneficial to add 1 mM Mn2+ and 100 mM Ca2+, respectively. A high titer of 12 084 IU/mL nisin could be reached, which is comparable to the highest titers reported using expensive, rich media. Summing up, we here present a 100% natural, robust, and sustainable approach for producing food-grade nisin and acetoin from readily available dairy waste.

Phthalyl starch nanoparticles as prebiotics enhanced nisin production in Lactococcus lactis through the induction of mild stress in probiotics.

AIM OF THE STUDY: Effect of internalized phthalyl starch nanoparticles (PSNs) on the antimicrobial ability of Lactococcus lactis (LL) KCTC 2013. METHODS AND RESULTS: Phthalyl starch nanoparticles were prepared by self-assembly of phthalyl starch and the amount of the hydrophobic phthalic moieties were characterized by nuclear magnetic resonance: PSN1 (DS: 14·3 mol.%), PSN2 (DS: 17·8 mol.%) and PSN3 (DS: 30·4 mol.%). The sizes of PSN1, PSN2 and PSN3 measured by dynamic light scattering were 364·7, 248·4 and 213·4 nm, respectively, and the surface charges of PSNs measured by electrophoretic light scattering were negative charges and PSNs were spherical in shape according to scanning electron microscope. It was found that when PSNs were treated with LL, the PSNs were internalized into LL through nanoparticle size-, energy- and glucose transporter-dependent mechanisms. The internalization was confirmed by confocal laser scanning microscopy and fluorescence-activated cell sorting. Nisin was isolated and identified by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Also, more nisin was produced from PSNs-treated LL than untreated- or starch-treated LL. Co-culture assay and agar diffusion test were performed to test the antimicrobial ability. Antimicrobial ability against Gram-negative Escherichia coli k88, Salmonella gallinarum and Gram-positive Listeria monocytogenes of LL treated with PSNs was higher than that of untreated or starch-treated group. Finally, it was found that the expression level of stress response genes dnaK, dnaJ and groES was significantly higher in PSNs-treated groups compared with starch-treated group or LL alone. CONCLUSION: The internalization of PSNs into LL enhanced the production of nisin through mild intracellular stimulation, resulting in enhanced antimicrobial ability. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows the promising potential of PSNs as new prebiotics for increasing the production of nisin, thus demonstrating a new method for the biological production of such antimicrobial peptides.

Improving nisin production by encapsulated Lactococcus lactis with starch/carboxymethyl cellulose edible films.

In this study, Lactococcus lactis was embedded in a film of corn starch (NS) and carboxymethyl cellulose (CMC) prepared using a casting method. At a CMC:NS ratio of 5:5, the composite film had the best comprehensive properties. Scanning electron microscopy images clearly showed that L. lactis was effectively embedded. The film with 1.5 % L. lactis showed the best performance and the lowest water vapor transmission rate (5.54 × 10-11 g/m s Pa. In addition, the edible film retained a viable count of 5.64 log CFU/g of L. lactis when stored at 4 °C for 30 days. The composite film with 1.5 % L. lactis showed the highest release of nisin (3.35 mg/mL) and good antibacterial activity against Staphylococcus aureus (53.53 %) after 8 days. Therefore, this edible film is a viable alternative antimicrobial strategy for the active packaging of foods containing low moisture content.

Conditions of nisin production by Lactococcus lactis subsp. lactis and its main uses as a food preservative.

Nisin is a small peptide produced by Lactococcus lactis ssp lactis that is currently industrially produced. This preservative is often used for growth prevention of pathogenic bacteria contaminating the food products. However, the use of nisin as a food preservative is limited by its low production during fermentation. This low production is mainly attributed to the multitude of parameters influencing the fermentation progress such as bacterial cells activity, growth medium composition (namely carbon and nitrogen sources), pH, ionic strength, temperature, and aeration. This review article focuses on the main parameters that affect nisin production by Lactococcus lactis bacteria. Moreover, nisin applications as a food preservative and the main strategies generally used are also discussed.

Engineering Lactococcus lactis as a multi-stress tolerant biosynthetic chassis by deleting the prophage-related fragment.

BACKGROUND: In bioengineering, growth of microorganisms is limited because of environmental and industrial stresses during fermentation. This study aimed to construct a nisin-producing chassis Lactococcus lactis strain with genome-streamlined, low metabolic burden, and multi-stress tolerance characteristics. RESULTS: The Cre-loxP recombination system was applied to reduce the genome and obtain the target chassis strain. A prophage-related fragment (PRF; 19,739 bp) in the L. lactis N8 genome was deleted, and the mutant strain L. lactis N8-1 was chosen for multi-stress tolerance studies. Nisin immunity of L. lactis N8-1 was increased to 6500 IU/mL, which was 44.44% higher than that of the wild-type L. lactis N8 (4500 IU/mL). The survival rates of L. lactis N8-1 treated with lysozyme for 2 h and lactic acid for 1 h were 1000- and 10,000-fold higher than that of the wild-type strain, respectively. At 39 â„ƒ, the L. lactis N8-1 could still maintain its growth, whereas the growth of the wild-type strain dramatically dropped. Scanning electron microscopy showed that the cell wall integrity of L. lactis N8-1 was well maintained after lysozyme treatment. Tandem mass tags labeled quantitative proteomics revealed that 33 and 9 proteins were significantly upregulated and downregulated, respectively, in L. lactis N8-1. These differential proteins were involved in carbohydrate and energy transport/metabolism, biosynthesis of cell wall and cell surface proteins. CONCLUSIONS: PRF deletion was proven to be an efficient strategy to achieve multi-stress tolerance and nisin immunity in L. lactis, thereby providing a new perspective for industrially obtaining engineered strains with multi-stress tolerance and expanding the application of lactic acid bacteria in biotechnology and synthetic biology. Besides, the importance of PRF, which can confer vital phenotypes to bacteria, was established.

Subcellular Localization and Assembly Process of the Nisin Biosynthesis Machinery in Lactococcus lactis.

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.

Synthesis and Characterization of Heterodimers and Fluorescent Nisin Species by Incorporation of Methionine Analogues and Subsequent Click Chemistry.

Noncanonical amino acids form a highly diverse pool of building blocks that can render unique physicochemical properties to peptides and proteins. Here, four methionine analogues with unsaturated and varying side chain lengths were successfully incorporated at four different positions in nisin in Lactococcus lactis through force feeding. This approach allows for residue-specific incorporation of methionine analogues into nisin to expand their structural diversity and alter their activity profiles. Moreover, the insertion of methionine analogues with biorthogonal chemical reactivity, e.g., azidohomoalanine and homopropargylglycine, provides the opportunity for chemical coupling to functional moieties and fluorescent probes as well as for intermolecular coupling of nisin variants. All resulting nisin conjugates retained antimicrobial activity, which substantiates the potential of this method as a tool to further study its localization and mode of action.

MiniBacillus PG10 as a Convenient and Effective Production Host for Lantibiotics.

Efficient bacterial cell factories are important for the screening and characterization of potent antimicrobial peptides such as lantibiotics. Although lantibiotic production systems have been established in Lactococcus lactis and Escherichia coli, the industrial workhorse Bacillus subtilis has been left relatively unexplored as a lantibiotic production host. Therefore, we tested different B. subtilis strains for their ability to produce lantibiotic peptides by using the subtilin modification and transport enzymes derived from the natural subtilin producer B. subtilis ATCC 6633. Our study shows that although B. subtilis ATCC 6633 and 168 are able to produce various processed lantibiotic peptides, an evident advantage of using either the 8-fold protease-deficient strain WB800 or the genome-minimized B. subtilis 168 strain PG10 is the lack of extracellular serine protease activity. Consequently, leader processing of lantibiotic precursor peptides is circumvented and thus potential toxicity toward the production host is prevented. Furthermore, PG10 provides a clean secondary metabolic background and therefore appears to be the most promising B. subtilis lantibiotic production host. We demonstrate the production of various lantibiotic precursor peptides by PG10 and show different options for their in vitro activation. Our study thus provides a convenient B. subtilis-based lantibiotic production system, which facilitates the search for novel antimicrobial peptides.

Genome-scale exploration of transcriptional regulation in the nisin Z producer Lactococcus lactis subsp. lactis IO-1.

Transcription is of the most crucial steps of gene expression in bacteria, whose regulation guarantees the bacteria's ability to adapt to varying environmental conditions. Discovering the molecular basis and genomic principles of the transcriptional regulation is thus one of the most important tasks in cellular and molecular biology. Here, a comprehensive phylogenetic footprinting framework was implemented to predict maximal regulons of Lactococcus lactis subsp. lactis IO-1, a lactic acid bacterium known for its high potentials in nisin Z production as well as efficient xylose consumption which have made it a promising biotechnological strain. A total set of 321 regulons covering more than 90% of all the bacterium's operons have been elucidated and validated according to available data. Multiple novel biologically-relevant members were introduced amongst which arsC, mtlA and mtl operon for BusR, MtlR and XylR regulons can be named, respectively. Moreover, the effect of riboflavin on nisin biosynthesis was assessed in vitro and a negative correlation was observed. It is believed that understandings from such networks not only can be useful for studying transcriptional regulatory potentials of the target organism but also can be implemented in biotechnology to rationally design favorable production conditions.

d-Methionine and d-Phenylalanine Improve Lactococcus lactis F44 Acid Resistance and Nisin Yield by Governing Cell Wall Remodeling.

Lactococcus lactis encounters various environmental challenges, especially acid stress, during its growth. The cell wall can maintain the integrity and shape of the cell under environmental stress, and d-amino acids play an important role in cell wall synthesis. Here, by analyzing the effects of 19 different d-amino acids on the physiology of L. lactis F44, we found that exogenously supplied d-methionine and d-phenylalanine increased the nisin yield by 93.22% and 101.29%, respectively, as well as significantly increasing the acid resistance of L. lactis F44. The composition of the cell wall in L. lactis F44 with exogenously supplied d-Met or d-Phe was further investigated via a vancomycin fluorescence experiment and a liquid chromatography-mass spectrometry assay, which demonstrated that d-Met could be incorporated into the fifth position of peptidoglycan (PG) muropeptides and d-Phe could be added to the fourth and fifth positions. Moreover, overexpression of the PG synthesis gene murF further enhanced the levels of d-Met and d-Phe involved in PG and increased the survival rate under acid stress and the nisin yield of the strain. This study reveals that the exogenous supply of d-Met or d-Phe can change the composition of the cell wall and influence acid tolerance as well as nisin yield in L. lactisIMPORTANCE As d-amino acids play an important role in cell wall synthesis, we analyzed the effects of 19 different d-amino acids on L. lactis F44, demonstrating that d-Met and d-Phe can participate in peptidoglycan (PG) synthesis and improve the acid resistance and nisin yield of this strain. murF overexpression further increased the levels of d-Met and d-Phe incorporated into PG and contributed to the acid resistance of the strain. These findings suggest that d-Met and d-Phe can be incorporated into PG to improve the acid resistance and nisin yield of L. lactis, and this study provides new ideas for the enhancement of nisin production.

First evidence of production of the lantibiotic nisin P.

Nisin P is a natural nisin variant, the genetic determinants for which were previously identified in the genomes of two Streptococcus species, albeit with no confirmed evidence of production. Here we describe Streptococcus agalactiae DPC7040, a human faecal isolate, which exhibits antimicrobial activity against a panel of gut and food isolates by virtue of producing nisin P. Nisin P was purified, and its predicted structure was confirmed by nanoLC-MS/MS, with both the fully modified peptide and a variant without rings B and E being identified. Additionally, we compared its spectrum of inhibition and minimum inhibitory concentration (MIC) with that of nisin A and its antimicrobial effect in a faecal fermentation in comparison with nisin A and H. We found that its antimicrobial activity was less potent than nisin A and H, and we propose a link between this reduced activity and the peptide structure.

Higher nisin yield is reached with glutathione and pyruvate compared with heme in Lactococcus lactis N8.

There are different studies that aim to enhance the production of nisin by Lactococcus lactis since its chemical synthesis is not possible. In this study, glutathione (GSH) and pyruvate, which are known to reduce the oxidative stress of cells, have been shown to trigger the production of nisin at both transcriptional and translational levels in L. lactis cells grown under aerobic condition. Presence of GSH and pyruvate caused more nisin yield than the heme-supplemented medium. Moreover, the expression of genes that encode stress-related enzymes were apparently upregulated in the presence of GSH and pyruvate. It can be concluded that GSH and pyruvate contribute to the defense system of L. lactis cells and so that higher biomass was obtained which in turn enhance nisin production. Antioxidant effect of GSH and pyruvate was known; however, their stimulating effect on nisin production was shown for the first time in this study.

Batch and fed-batch production of probiotic biomass and nisin in nutrient-supplemented whey media.

The production of a highly concentrated probiotic preparation of Lactococcus lactis CECT 539 was studied in both batch and realkalized fed-batch fermentations in diluted whey (DW) media (DW25, DW50, DW75, DW100, and DW125) supplemented with MRS broth nutrients (except glucose and Tween 80) at 25, 50, 75, 100, and 125% of their standard concentrations in the complex medium. The fed-batch culture using DW100 medium provided the highest concentrations of probiotic biomass (5.98 g/L) and nisin (258.47 BU/mL), which were obtained at lower production costs than those estimated for the fed-batch culture in DW medium. The batch and fed-batch cultures reduced the initial chemical oxygen demand (COD) of the media by 29.1-41.7% and 31.2-54.2%, respectively. Graphical abstract.

Systematic characterization of position one variants within the lantibiotic nisin.

Lantibiotics are a growing class of natural compounds, which possess antimicrobial activity against a broad range of Gram-positive bacteria. Their high potency against human pathogenic strains such as MRSA and VRE makes them excellent candidates as substitutes for classic antibiotics in times of increasing multidrug resistance of bacterial strains. New lantibiotics are detected in genomes and can be heterologously expressed. The functionality of these novel lantibiotics requires a systematic purification and characterization to benchmark them against for example the well-known lantibiotic nisin. Here, we used a standardized workflow to characterize lantibiotics consisting of six individual steps. The expression and secretion of the lantibiotic was performed employing the promiscuous nisin modification machinery. We mutated the first amino acid of nisin into all proteinaceous amino acids and compared their bactericidal potency against sensitive strains as well as strains expressing nisin resistance proteins. Interestingly, we can highlight four distinct groups based on the residual activity of nisin against sensitive as well as resistant L. lactis strains.