Regulation of nisin biosynthesis and immunity in Lactococcus lactis 6F3

Lyophilized cell-free supernatants of Limosilactobacillus fermentum T0701 exhibited antibacterial activity against Helicobacter pylori

Helicobacter pylori is a prominent gastrointestinal pathogen associated with various gastrointestinal illnesses. It presents substantial health risks due to its antibiotic resistance. Therefore, it is crucial to identify alternative treatments for H. pylori infections. Limosilactobacillus spp exhibit probiotic properties with beneficial effects in humans; however, the mechanisms by which it counteracts H. pylori infection are unknown. This study aimed to evaluate the potential of Limosilactobacillus fermentum T0701 lyophilized cell-free supernatants (LCFS) against H. pylori. The LCFS has varying antimicrobial activities, with inhibition zones of up to 10.67 mm. The minimum inhibitory concentration and minimum bacterial concentration of LCFS are 6.25-25.00 mg/mL and 6.25 mg/mL to > 50.00 mg/mL, respectively, indicating its capability to inhibit H. pylori. There is morphological damage observed in H. pylori treated with LCFS. Additionally, H. pylori adhesion to AGS cells (human gastric adenocarcinoma epithelial cells) reduces by 74.23%, highlighting the LCFS role in preventing bacterial colonization. Moreover, LCFS exhibits no cytotoxicity or morphological changes in AGS cells, and with no detected virulence or antimicrobial resistance genes, further supporting its safety profile. L. fermentum T0701 LCFS shows promise as a safe and effective non-toxic agent against H. pylori, with the potential to prevent gastric colonization.

Exposure and resistance to lantibiotics impact microbiota composition and function

The intestinal microbiota is composed of hundreds of distinct microbial species that interact with each other and their mammalian host. Antibiotic exposure dramatically impacts microbiota compositions and leads to acquisition of antibiotic-resistance genes. Lantibiotics are ribosomally synthesized and post-translationally modified peptides produced by some bacterial strains to inhibit the growth of competing bacteria. Nisin A is a lantibiotic produced by Lactococcus lactis that is commonly added to food products to reduce contamination with Gram-positive pathogens. Little is known, however, about lantibiotic-resistance of commensal bacteria inhabiting the human intestine. Herein, we demonstrate that Nisin A administration to mice alters fecal microbiome compositions and the concentration of taurine-conjugated primary bile acids. Lantibiotic Resistance System genes (LRS) are encoded by lantibiotic-producing bacterial strains but, we show, are also prevalent in microbiomes across human cohorts spanning vastly different lifestyles and 5 continents. Bacterial strains encoding LRS have enhanced in vivo fitness upon dietary exposure to Nisin A but reduced fitness in the absence of lantibiotic pressure. Differential binding of host derived, secreted IgA contributes to fitness discordance between bacterial strains encoding or lacking LRS. Although LRS are associated with mobile genetic elements, sequence comparisons of LRS encoded by distinct bacterial species suggest they have been long-term components of their respective genomes. Our study reveals the prevalence, abundance and physiologic significance of an underappreciated subset of antimicrobial resistance genes encoded by commensal bacterial species constituting the human gut microbiome, and provides insights that will guide development of microbiome augmenting strategies.

Hub genes and pathways related to caries-free dental biofilm: clinical metatranscriptomic study

OBJECTIVE

This study aimed to evaluate the microbial functional profile of biofilms related to caries-free (CF, n = 6) and caries-arrested (CI, n = 3) compared to caries-active (CA, n = 5) individuals.

MATERIALS AND METHODS

A metatranscriptomic was performed in supragingival biofilm from different clinical conditions related to caries or health. Total RNA was extracted and cDNAs were obtained and sequenced (Illumina HiSeq3000). Trimmed data (SortMeRNA) were submitted to the SqueezeMeta pipeline in the co-assembly mode for functional analysis and further differential gene expression analysis (DESeq2) and weighted gene co-expression network analysis (WCGNA) to explore and identify gene modules related to these clinical conditions.

RESULTS

A total of 5303 genes were found in the metatranscriptomic analysis. A co-expression network identified the most relevant modules strongly related to specific caries status. Correlation coefficients were calculated between the eigengene modules and the clinical conditions (CA, CI, and CF) discriminating multiple modules. CA and CI showed weak correlation coefficient strength across the modules, while the CF condition presented a very strong positive correlation coefficient (r = 0.9, p value = 4 × 10-9). Pearson's test was applied to further analyze the module membership and gene significance in CF conditions, and the most relevant were HSPA1s-K03283, Epr- K13277, and SLC1A-K05613. Gene Ontology (GO) shows important bioprocesses, such as two-component system, fructose and mannose metabolism, pentose and glucuronate interconversions, and flagellar assembly (p-adjust < 0.05). The ability to use different carbohydrates, integrate multiple signals, swarm, and bacteriocin production are significant metabolic advantages in the oral environment related to CF.

CONCLUSIONS

A distinct functional health profile could be found in CF, where co-occurring genes can act in different pathways at the same time. Genes HSPA1s, Epr, and SLC1A may be appointed as potential biomarkers for caries-free biofilms.

CLINICAL RELEVANCE

Potential biomarkers for caries-free biofilms could contribute to the knowledge of caries prevention and control.

Bacteriocin: A natural approach for food safety and food security

The call to cater for the hungry is a worldwide problem in the 21st century. Food security is the utmost prime factor for the increasing demand for food. Awareness of human health when using chemical preservatives in food has increased, resulting in the use of alternative strategies for preserving food and enhancing its shelf-life. New preservatives along with novel preservation methods have been instigated, due to the intensified demand for extended shelf-life, along with prevention of food spoilage of dairy products. Bacteriocins are the group of ribosomally synthesized antimicrobial peptides; they possess a wide range of biological activities, having predominant antibacterial activity. The bacteriocins produced by the lactic acid bacteria (LAB) are considered to be of utmost importance, due to their association with the fermentation of food. In recent times among various groups of bacteriocins, leaderless and circular bacteriocins are gaining importance, due to their extensive application in industries. These groups of bacteriocins have been least studied as they possess peculiar structural and biosynthetic mechanisms. They chemically possess N-to-C terminal covalent bonds having a predominant peptide background. The stability of the bacteriocins is exhibited by the circular structure. Up till now, very few studies have been performed on the molecular mechanisms. The structural genes associated with the bacteriocins can be combined with the activity of various proteins which are association with secretion and maturation. Thus the stability of the bacteriocins can be used effectively in the preservation of food for a longer period of time. Bacteriocins are thermostable, pH-tolerant, and proteolytically active in nature, which make their usage convenient to the food industry. Several research studies are underway in the domain of biopreservation which can be implemented in food safety and food security.

Heterologous Protein Production in Lactobacillus (plantarum) Using pSIP Vectors

While lactobacilli are not generally regarded as efficient cell factories for heterologous proteins, these food-grade Gram-positive bacteria are attractive as expression hosts for medicinal proteins. Furthermore, tools have been developed not only to secrete the protein of interest, but also to anchor the protein to the cell membrane or the cell wall. Research efforts aimed at the production and surface display of complex vaccine proteins have shown that lactobacilli are capable of producing heterologous proteins that are otherwise difficult to produce in soluble form. Many recent studies on expressing a wide variety of proteins in lactobacilli have employed the pSIP vector system, which offers a wide range of possibilities for inducible expression, including various options for secretion and surface anchoring. The modular nature of the pSIP vectors allows for rapid screening of multiple expression strategies. This chapter describes the pSIP vector system and how it can be used to accomplish protein expression in lactobacilli.

Gene-Trait Matching and Prevalence of Nisin Tolerance Systems in Lactococus lactis

Lactococcus lactis cheese starter cultures typically contain a mix of many strains and may include variants that produce and/or tolerate the antimicrobial bacteriocin nisin. Nisin is well-established as an effective agent against several undesirable Gram-positive bacteria in cheese and various other foods. In the current study, we have examined the effect of nisin on 710 individual L. lactis strains during milk fermentations. Changes in milk acidification profiles with and without nisin exposure, ranging from unaltered acidification to loss of acidification, could be largely explained by the type(s) and variants of nisin immunity and nisin degradation genes present, but surprisingly, also by genotypic lineage (L. lactis ssp. cremoris vs. ssp. lactis). Importantly, we identify that nisin degradation by NSR is frequent among L. lactis and therefore likely the main mechanism by which dairy-associated L. lactis strains tolerate nisin. Insights from this study on the strain-specific effect of nisin tolerance and degradation during milk acidification is expected to aid in the design of nisin-compatible cheese starter cultures.

Engineered Akkermansia muciniphila: A promising agent against diseases (Review)

Achieving a harmonious gut microbial ecosystem has been hypothesized to be a successful method for alleviating metabolic disorders. The administration of probiotics, such as Lactobacillus and Bifidobacteria, is a known traditional and safe pathway to regulate human commensal microbes. With advancements in genetic sequencing and genetic editing tools, more bacteria are able to function as engineered probiotics with multiple therapeutic properties. As one of the next-generation probiotic candidates, Akkermansia muciniphila (A. muciniphila) has been discovered to enhance the gut barrier function and moderate inflammatory responses, exhibit improved effects with pasteurization and display beneficial probiotic effects in individuals with obesity, type 2 diabetes, atherosclerosis and autism-related gastrointestinal disturbances. In view of this knowledge, the present review aimed to summarize the effects of A. muciniphila in the treatment of metabolic disorders and to discuss several mature recombination systems for the genetic modification of A. muciniphila. From gaining an enhanced understanding of its genetic background, ingested A. muciniphila is expected to be used in various applications, including as a diagnostic tool, and in the site-specific delivery of therapeutic drugs.

LanI-Mediated Lantibiotic Immunity in Bacillus subtilis: Functional Analysis

Lantibiotics subtilin and nisin are produced by Bacillus subtilis and Lactococcus lactis, respectively. To prevent toxicity of their own lantibiotic, both bacteria express specific immunity proteins, called SpaI and NisI. In addition, ABC transporters SpaFEG and NisFEG prevent lantibiotic toxicity by transporting the respective peptides to the extracellular space. Although the three-dimensional structures of SpaI and NisI have been solved, very little is known about the molecular function of either lipoprotein. Using laser-induced liquid bead ion desorption (LILBID)-mass spectrometry, we show here that subtilin interacts with SpaI monomers. The expression of either SpaI or NisI in a subtilin-nonproducing B. subtilis strain resulted in the respective strain being more resistant against either subtilin or nisin. Furthermore, pore formation provided by subtilin and nisin was prevented specifically upon the expression of either SpaI or NisI. As shown with a nisin-subtilin hybrid molecule, the C-terminal part of subtilin but not any particular lanthionine ring was needed for SpaI-mediated immunity. With respect to growth, SpaI provided less immunity against subtilin than is provided by the ABC transporter SpaFEG. However, SpaI prevented pore formation much more efficiently than SpaFEG. Taken together, our data show the physiological function of SpaI as a fast immune response to protect the cellular membrane.IMPORTANCE The two lantibiotics nisin and subtilin are produced by Lactococcus lactis and Bacillus subtilis, respectively. Both peptides have strong antimicrobial activity against Gram-positive bacteria, and therefore, appropriate protection mechanisms are required for the producing strains. To prevent toxicity of their own lantibiotic, both bacteria express immunity proteins, called SpaI and NisI, and in addition, ABC transporters SpaFEG and NisFEG. Whereas it has been shown that the ABC transporters protect the producing strains by transporting the toxic peptides to the extracellular space, the exact mode of action and the physiological function of the lipoproteins during immunity are still unknown. Understanding the exact role of lantibiotic immunity proteins is of major importance for improving production rates and for the design of newly engineered peptide antibiotics. Here, we show (i) the specificity of each lipoprotein for its own lantibiotic, (ii) the specific physical interaction of subtilin with its lipoprotein SpaI, (iii) the physiological function of SpaI in protecting the cellular membrane, and (iv) the importance of the C-terminal part of subtilin for its interaction with SpaI.

Contribution of YthA, a PspC Family Transcriptional Regulator of Lactococcus lactis F44 Acid Tolerance and Nisin Yield: a Transcriptomic Approach

To overcome the adverse impacts of environmental stresses during growth, different adaptive regulation mechanisms can be activated in Lactococcus lactis In this study, the transcription levels of eight transcriptional regulators of L. lactis subsp. lactis F44 under acid stress were analyzed using quantitative reverse transcription-PCR. Eight gene-overexpressing strains were then constructed to examine their influences on acid-resistant capability. Overexpressing ythA, a PspC family transcriptional regulator, increased the survival rate by 3.2-fold compared to the control at the lethal pH 3.0 acid shock. Moreover, the nisin yield was increased by 45.50%. The ythA-overexpressing strain FythA appeared to have higher intracellular pH stability and nisin-resistant ability. Subsequently, transcriptome analysis revealed that the vast majority of genes associated with amino acid biosynthesis, including arginine, serine, phenylalanine, and tyrosine, were predominantly upregulated in FythA. Arginine biosynthesis (argG and argH), arginine deiminase pathway, and polar amino acid transport (ysfE and ysfF) were proposed to be the main regulation mechanisms of YthA. Furthermore, the transcription of genes associated with pyrimidine and exopolysaccharide biosynthesis were upregulated. The transcriptional levels of nisIPRKFEG genes were substantially higher in FythA, which directly contributed to the yield and resistance of nisin. Three potential DNA-binding sequences were predicted by computer analysis using the upstream regions of genes with prominent changes. This study showed that YthA could increase acid resistance and nisin yield and revealed a putative regulation mechanism of YthA.IMPORTANCE Nisin, produced by Lactococcus lactis subsp. lactis, is widely used as a safe food preservative. Acid stress becomes the primary restrictive factor of cell growth and nisin yield. In this research, we found that the transcriptional regulator YthA was conducive to enhancing the acid resistance of L. lactis F44. Overexpressing ythA could significantly improve the survival rate and nisin yield. The stability of intracellular pH and nisin resistance were also increased. Transcriptome analysis showed that nisin immunity and the biosynthesis of some amino acids, pyrimidine, and exopolysaccharides were enhanced in the engineered strain. This study elucidates the regulation mechanism of YthA and provides a novel strategy for constructing robust industrial L. lactis strains.

Contribution of YthA, a PspC Family Transcriptional Regulator of Lactococcus lactis F44 Acid Tolerance and Nisin Yield: a Transcriptomic Approach

To overcome the adverse impacts of environmental stresses during growth, different adaptive regulation mechanisms can be activated in Lactococcus lactis In this study, the transcription levels of eight transcriptional regulators of L. lactis subsp. lactis F44 under acid stress were analyzed using quantitative reverse transcription-PCR. Eight gene-overexpressing strains were then constructed to examine their influences on acid-resistant capability. Overexpressing ythA, a PspC family transcriptional regulator, increased the survival rate by 3.2-fold compared to the control at the lethal pH 3.0 acid shock. Moreover, the nisin yield was increased by 45.50%. The ythA-overexpressing strain FythA appeared to have higher intracellular pH stability and nisin-resistant ability. Subsequently, transcriptome analysis revealed that the vast majority of genes associated with amino acid biosynthesis, including arginine, serine, phenylalanine, and tyrosine, were predominantly upregulated in FythA. Arginine biosynthesis (argG and argH), arginine deiminase pathway, and polar amino acid transport (ysfE and ysfF) were proposed to be the main regulation mechanisms of YthA. Furthermore, the transcription of genes associated with pyrimidine and exopolysaccharide biosynthesis were upregulated. The transcriptional levels of nisIPRKFEG genes were substantially higher in FythA, which directly contributed to the yield and resistance of nisin. Three potential DNA-binding sequences were predicted by computer analysis using the upstream regions of genes with prominent changes. This study showed that YthA could increase acid resistance and nisin yield and revealed a putative regulation mechanism of YthA.IMPORTANCE Nisin, produced by Lactococcus lactis subsp. lactis, is widely used as a safe food preservative. Acid stress becomes the primary restrictive factor of cell growth and nisin yield. In this research, we found that the transcriptional regulator YthA was conducive to enhancing the acid resistance of L. lactis F44. Overexpressing ythA could significantly improve the survival rate and nisin yield. The stability of intracellular pH and nisin resistance were also increased. Transcriptome analysis showed that nisin immunity and the biosynthesis of some amino acids, pyrimidine, and exopolysaccharides were enhanced in the engineered strain. This study elucidates the regulation mechanism of YthA and provides a novel strategy for constructing robust industrial L. lactis strains.

Crystal Structure of NisI in a Lipid-Free Form, the Nisin Immunity Protein, from Lactococcus lactis

Nisin is a lantibiotic, a member of a family of polypeptides containing lanthionine with antimicrobial activity. Nisin-producing microorganisms require immunity proteins for self-protection from nisin itself. Lactococcus lactis, a microorganism that synthesizes nisin, has an integral NisFEG ABC transporter and an NisI lipoprotein that function in nisin immunity. Here, we present the crystal structure of the full length of NisI_22-C, a lipid-free form of NisI, determined at 1.9-Å resolution. As with the nuclear magnetic resonance (NMR) structures of the N- and C-terminal domains of NisI, NisI_22-C is composed of N- and C-terminal domains, both of which display a fold similar to that found in SpaI, a lipoprotein with immunity against subtilin in Bacillus subtilis The full-length structure of NisI_22-c reveals a large, deep cleft by the interdomain association, one side of which is occupied by the residues important for immunity. Opposite the cleft, a shallow groove is found where nisin-interacting residues are distributed in the periphery composed of the C-terminal negative patch. Based on a sulfate ion found in the large and deep cleft, a model of NisI in complex with a farnesyl diphosphate backbone of lipid II is proposed, suggesting a mechanism for increasing the chances of encountering nisin.

CerR, a Single-Domain Regulatory Protein of the LuxR Family, Promotes Cerecidin Production and Immunity in Bacillus cereus

Cerecidins are small lantibiotics from Bacillus cereus that were obtained using a semi-in vitro biosynthesis strategy and showed prominent antimicrobial activities against certain Gram-positive bacteria. However, the parental strain B. cereus As 1.1846 is incapable of producing cerecidins, most probably due to the transcriptional repression of the cerecidin gene cluster. Located in the cerecidin gene cluster, cerR encodes a putative response regulator protein that belongs to the LuxR family transcriptional regulators. CerR (84 amino acids) contains only a conserved DNA binding domain and lacks a conventional phosphorylation domain, which is rarely found in lantibiotic gene clusters. To investigate its function in cerecidin biosynthesis, cerR was constitutively expressed in B. cereus As 1.1846. Surprisingly, Constitutive expression of cerR enabled the production of cerecidins and enhanced self-immunity of B. cereus toward cerecidins. Reverse transcription-PCR analysis and electrophoresis mobility shift assays indicated, respectively, that the cer cluster was transcribed in two transcripts (cerAM and cerRTPFE) and that CerR regulated the cerecidin gene cluster directly by binding to the two predicted promoter regions of cerA and cerR DNase I footprinting experiments further confirmed that CerR specifically bound to the two promoter regions at a conserved inverted repeat sequence that was designated a CerR binding motif (cerR box). The present study demonstrated that CerR, as the first single-domain LuxR family transcriptional regulator, serves as a transcriptional activator in cerecidin biosynthesis and activates the cerecidin gene cluster, which was otherwise cryptic in B. cereusIMPORTANCE Lantibiotics with intriguing and prominent bioactivities are potential peptide antibiotics that could be applied in many areas, including food and pharmaceutical industries. The biosynthesis of lantibiotics is generally controlled by two-component regulatory systems consisting of histidine kinases and response regulators, while some unique and interesting regulatory systems are also revealed with the ever-increasing discovery of lantibiotic gene clusters among diverse microorganisms. Dissection of diverse lantibiotic regulation machineries would permit deep understanding of the biological functions of lantibiotics in different niches and even enable genetic activation of lantibiotic gene clusters that are otherwise cryptic. The significance of our study is to illuminate the regulatory mechanism of a special single-domain protein, CerR, in regulating cerecidin biosynthesis in Bacillus cereus, providing a possible novel approach to activate cryptic lantibiotic clusters.

The role of the CroR response regulator in resistance of Enterococcus faecalis to D-cycloserine is defined using an inducible receiver domain

Enterococcus faecalis is an opportunistic multidrug-resistant human pathogen causing severe nosocomial infections. Previous investigations revealed that the CroRS two-component regulatory pathway likely displays a pleiotropic role in E. faecalis, involved in virulence, macrophage survival, oxidative stress response as well as antibiotic resistance. Therefore, CroRS represents an attractive potential new target for antibiotherapy. In this report, we further explored CroRS cellular functions by characterizing the CroR regulon: the 'domain swapping' method was applied and a CroR chimera protein was generated by fusing the receiver domain from NisR to the output domain from CroR. After demonstrating that the chimera CroR complements a croR gene deletion in E. faecalis (stress response, virulence), we conducted a global gene expression analysis using RNA-Seq and identified 50 potential CroR targets involved in multiple cellular functions such as cell envelope homeostasis, substrate transport, cell metabolism, gene expression regulation, stress response, virulence and antibiotic resistance. For validation, CroR direct binding to several candidate targets was demonstrated by EMSA. Further, this work identified alr, the gene encoding the alanine racemase enzyme involved in E. faecalis resistance to D-cycloserine, a promising antimicrobial drug to treat enterococcal infections, as a member of the CroR regulon.

Bacteriocins as food preservatives: Challenges and emerging horizons

The increasing demand for fresh-like food products and the potential health hazards of chemically preserved and processed food products have led to the advent of alternative technologies for the preservation and maintenance of the freshness of the food products. One such preservation strategy is the usage of bacteriocins or bacteriocins producing starter cultures for the preservation of the intended food matrixes. Bacteriocins are ribosomally synthesized smaller polypeptide molecules that exert antagonistic activity against closely related and unrelated group of bacteria. This review is aimed at bringing to lime light the various class of bacteriocins mainly from gram positive bacteria. The desirable characteristics of the bacteriocins which earn them a place in food preservation technology, the success story of the same in various food systems, the various challenges and the strategies employed to put them to work efficiently in various food systems has been discussed in this review. From the industrial point of view various aspects like the improvement of the producer strains, downstream processing and purification of the bacteriocins and recent trends in engineered bacteriocins has also been briefly discussed in this review.

Specificity of Subtilin-Mediated Activation of Histidine Kinase SpaK

Autoinduction via two-component systems is a widespread regulatory mechanism that senses environmental and metabolic changes. Although the lantibiotics nisin and subtilin are closely related and share the same lanthionine ring structure, they autoinduce their biosynthesis in a highly specific manner. Subtilin activates only the two-component system SpaRK of Bacillus subtilis, whereas nisin activates solely the two-component system NisRK of Lactococcus lactis To identify components that determine the specificity of subtilin autoinduction, several variants of the respective lantibiotics were analyzed for their autoinductive capacities. Here, we show that amino acid position 20 is crucial for SpaK activation, as an engineered nisin molecule with phenylalanine at position 20 (nisin N20F) was able to activate SpaK in a specific manner. In combination with the N-terminal tryptophan of subtilin (nisin I1W/N20F), SpaK autoinduction reached almost the level of subtilin-mediated autoinduction. Furthermore, the overall structure of subtilin is also important for its association with the histidine kinase. The destruction of the second lanthionine ring (subtilin C11A, ring B), as well as mutations that interfere with the flexibility of the hinge region located between lanthionine rings C and D (subtilin L21P/Q22P), abolished SpaK autoinduction. Although the C-terminal part of subtilin is needed for efficient SpaK autoinduction, the destruction of lanthionine rings D and E had no measurable impact. Based on these findings, a model for the interaction of subtilin with histidine kinase SpaK was established.IMPORTANCE Although two-component systems are important regulatory systems that sense environmental changes, very little information on the molecular mechanism of sensing or the interaction of the sensor with its respective kinase is available. The strong specificity of linear lantibiotics such as subtilin and nisin for their respective kinases provides an excellent model system to unravel the structural needs of these lantibiotics for activating histidine kinases in a specific manner. More than that, the biosyntheses of lantibiotics are autoinduced via two-component systems. Therefore, an understanding of their interactions with histidine kinases is needed for the biosynthesis of newly engineered peptide antibiotics. Using a Bacillus subtilis-based reporter system, we were able to identify the molecular constraints that are necessary for specific SpaK activation and to provide SpaK specificity to nisin with just two point mutations.

Full-length nisin immunity protein NisI from Lactococcus lactis in a lipid-free form: crystallization and X-ray analysis

NisI is a lantibiotic-binding lipoprotein that is specific for nisin. Nisin-producing microorganisms use NisI as an immunity protein for self-protection against nisin. Here, the purification, crystallization and preliminary X-ray diffraction of full-length NisI from Lactobacillus lactis in a lipid-free form (NisI22-C) are reported. Importantly, reductive methylation of the lysine residues in NisI22-C was essential for initial crystallization. Only methylated NisI22-C crystallized. The optimized crystals of methylated NisI22-C were grown in 30-40 mM ammonium sulfate, 0.1 M sodium acetate pH 4.6, 16-18% PEG 4000 at 295 K and diffracted to 1.9 Å resolution. The crystal belonged to space group P212121, with unit-cell parameters a = 45.99, b = 76.67, c = 76.39 Å, α = β = γ = 90.0°. Assuming the presence of one molecule in the asymmetric unit, the estimated Matthews coefficient (VM) is 2.58 Å3 Da-1 and the estimated solvent content is 52.3%.

Nisin as a Food Preservative: Part 1: Physicochemical Properties, Antimicrobial Activity, and Main Uses

Nisin is a natural preservative for many food products. This bacteriocin is mainly used in dairy and meat products. Nisin inhibits pathogenic food borne bacteria such as Listeria monocytogenes and many other Gram-positive food spoilage microorganisms. Nisin can be used alone or in combination with other preservatives or also with several physical treatments. This paper reviews physicochemical and biological properties of nisin, the main factors affecting its antimicrobial effectiveness, and its food applications as an additive directly incorporated into food matrices.

Ligand determinants of nisin for its induction activity

Nisin has been widely used in the food industry as a safe and natural preservative and has the potential to be used as a biomedicine. Improving nisin production is important for its enormous applications. Nisin A is produced in Lactococcus lactis and its biosynthesis is induced through the regulation of the 2-component system NisKR. In this study, alanine-scanning mutagenesis was applied to study the key structure or AA in nisin for inducing the 2-component system NisKR to regulate downstream gene expression. Assay of β-galactosidase activity revealed that either ring A or ring B was necessary for nisin to induce lacZ reporter gene expression. A substituted first ring formed by Thr2 and Cys7 in S3A instead of ring A (formed by Ser3 and Cys7) fully retained nisin induction activity. Mutation of cationic AA and addition of cationic ions hardly affected nisin induction activity. These results demonstrated that the N-terminal ring structures in nisin were involved in activating NisKR to act as an inducing molecule, whereas the electrostatic force might not contribute to this process. In addition, 2 specific residues were revealed to have potential for improving both nisin induction and antimicrobial activity, which might be used for increasing nisin production.

Structure of the Response Regulator NsrR from Streptococcus agalactiae, Which Is Involved in Lantibiotic Resistance

Lantibiotics are antimicrobial peptides produced by Gram-positive bacteria. Interestingly, several clinically relevant and human pathogenic strains are inherently resistant towards lantibiotics. The expression of the genes responsible for lantibiotic resistance is regulated by a specific two-component system consisting of a histidine kinase and a response regulator. Here, we focused on a response regulator involved in lantibiotic resistance, NsrR from Streptococcus agalactiae, and determined the crystal structures of its N-terminal receiver domain and C-terminal DNA-binding effector domain. The C-terminal domain exhibits a fold that classifies NsrR as a member of the OmpR/PhoB subfamily of regulators. Amino acids involved in phosphorylation, dimerization, and DNA-binding were identified and demonstrated to be conserved in lantibiotic resistance regulators. Finally, a model of the full-length NsrR in the active and inactive state provides insights into protein dimerization and DNA-binding.

The Solution Structure of the Lantibiotic Immunity Protein NisI and Its Interactions with Nisin

Many Gram-positive bacteria produce lantibiotics, genetically encoded and posttranslationally modified peptide antibiotics, which inhibit the growth of other Gram-positive bacteria. To protect themselves against their own lantibiotics these bacteria express a variety of immunity proteins including the LanI lipoproteins. The structural and mechanistic basis for LanI-mediated lantibiotic immunity is not yet understood. Lactococcus lactis produces the lantibiotic nisin, which is widely used as a food preservative. Its LanI protein NisI provides immunity against nisin but not against structurally very similar lantibiotics from other species such as subtilin from Bacillus subtilis. To understand the structural basis for LanI-mediated immunity and their specificity we investigated the structure of NisI. We found that NisI is a two-domain protein. Surprisingly, each of the two NisI domains has the same structure as the LanI protein from B. subtilis, SpaI, despite the lack of significant sequence homology. The two NisI domains and SpaI differ strongly in their surface properties and function. Additionally, SpaI-mediated lantibiotic immunity depends on the presence of a basic unstructured N-terminal region that tethers SpaI to the membrane. Such a region is absent from NisI. Instead, the N-terminal domain of NisI interacts with membranes but not with nisin. In contrast, the C-terminal domain specifically binds nisin and modulates the membrane affinity of the N-terminal domain. Thus, our results reveal an unexpected structural relationship between NisI and SpaI and shed light on the structural basis for LanI mediated lantibiotic immunity.

Autoinduction Specificities of the Lantibiotics Subtilin and Nisin

The biosynthesis of the lantibiotics subtilin and nisin is regulated by autoinduction via two-component systems. Although subtilin is structurally closely related to nisin and contains the same lanthionine ring structure, both lantibiotics specifically autoinduce their biosynthesis. Subtilin and also the subtilin-like lantibiotics entianin and ericin autoinduce the two-component system SpaRK of Bacillus subtilis, whereas the biosynthesis of nisin is autoinduced via the two-component system NisRK of Lactococcus lactis. Autoinduction is highly specific for the respective lantibiotic and therefore of major importance for the functional expression of genetically engineered subtilin-like lantibiotics. To identify the structural features required for subtilin autoinduction, subtilin-nisin hybrids and specific point mutations of amino acid position 1 were generated. For subtilin autoinduction, the N-terminal tryptophan is the most important for full SpaK activation. The failure of subtilin to autoinduce the histidine kinase NisK mainly depends on the N-terminal tryptophan, as its single exchange to the aliphatic amino acid residues isoleucine, leucine, and valine provided NisK autoinduction. In addition, the production of subtilin variants which did not autoinduce their own biosynthesis could be rescued upon heterologous coexpression in B. subtilis DSM15029 by the autoinducing subtilin-like lantibiotic entianin.

Activation of Histidine Kinase SpaK Is Mediated by the N-Terminal Portion of Subtilin-Like Lantibiotics and Is Independent of Lipid II

The biosynthesis of the lantibiotic subtilin is autoinduced in a quorum-sensing mechanism via histidine kinase SpaK. Subtilin-like lantibiotics, such as entianin, ericin S, and subtilin, specifically activated SpaK in a comparable manner, whereas the structurally similar nisin did not provide the signal for SpaK activation at nontoxic concentrations. Surprisingly, nevertheless, nisin if applied together with entianin partly quenched SpaK activation. The N-terminal entianin1-20 fragment (comprising N-terminal amino acids 1 to 20) was sufficient for SpaK activation, although higher concentrations were needed. The N-terminal nisin1-20 fragment also interfered with entianin-mediated activation of SpaK and, remarkably, at extremely high concentrations also activated SpaK. Our data show that the N-terminal entianin1-20 fragment is sufficient for SpaK activation. However, if present, the C-terminal part of the molecule further strongly enhances the activation, possibly by its interference with the cellular membrane. As shown by using lipid II-interfering substances and a lipid II-deficient mutant strain, lipid II is not needed for the sensing mechanism.

Bioengineering of the model lantibiotic nisin

The lantibiotics are a class of bacterially produced antimicrobial peptides (bacteriocins) that contain several unusual amino acids resulting from enzyme-mediated post-translational modifications. They exhibit high specific activity against Gram-positive targets, including many antibiotic-resistant pathogens, and consequently have been investigated with a view to their application as antimicrobials in both the food and medical arenas. Importantly, the gene-encoded nature of lantibiotics makes them more amenable to bioengineering strategies to further enhance their antimicrobial and physicochemical properties. However, although the bioengineering of lantibiotics has been underway for over 2 decades, significant progress has only been reported in recent years. This review charts recent developments with regard to the implementation of bioengineering strategies to enhance the functional characteristics of the prototypical and most studied lantibiotic nisin.

Identification of a proton-chloride antiporter (EriC) by Himar1 transposon mutagenesis in Lactobacillus reuteri and its role in histamine production

The gut microbiome may modulate intestinal immunity by luminal conversion of dietary amino acids to biologically active signals. The model probiotic organism Lactobacillus reuteri ATCC PTA 6475 is indigenous to the human microbiome, and converts the amino acid L-histidine to the biogenic amine, histamine. Histamine suppresses tumor necrosis factor (TNF) production by human myeloid cells and is a product of L-histidine decarboxylation, which is a proton-facilitated reaction. A transposon mutagenesis strategy was developed based on a single-plasmid nisin-inducible Himar1 transposase/transposon delivery system for L. reuteri. A highly conserved proton-chloride antiporter gene (eriC), a gene widely present in the gut microbiome was discovered by Himar1 transposon (Tn)-mutagenesis presented in this study. Genetic inactivation of eriC by transposon insertion and genetic recombineering resulted in reduced ability of L. reuteri to inhibit TNF production by activated human myeloid cells, diminished histamine production by the bacteria and downregulated expression of histidine decarboxylase cluster genes compared to those of WT 6475. EriC belongs to a large family of ion transporters that includes chloride channels and proton-chloride antiporters and may facilitate the availability of protons for the decarboxylation reaction, resulting in histamine production by L. reuteri. This report leverages the tools of bacterial genetics for probiotic gene discovery. The findings highlight the widely conserved nature of ion transporters in bacteria and how ion transporters are coupled with amino acid decarboxylation and contribute to microbiome-mediated immunomodulation.

Structure and protective efficacy of the Staphylococcus aureus autocleaving protease EpiP

Despite the global medical needs associated with Staphylococcus aureus infections, no licensed vaccines are currently available. We identified and characterized a protein annotated as an epidermin leader peptide processing serine protease (EpiP), as a novel S. aureus vaccine candidate. In addition, we determined the structure of the recombinant protein (rEpiP) by X-ray crystallography. The crystal structure revealed that rEpiP was cleaved somewhere between residues 95 and 100, and we found that the cleavage occurs through an autocatalytic intramolecular mechanism. The protein expressed by S. aureus cells also appeared to undergo a similar processing event. To determine whether the protein acts as a serine protease, we mutated the hypothesized catalytic serine 393 residue to alanine, generating rEpiP-S393A. The crystal structure of this mutant protein showed that the polypeptide chain was not cleaved and was not interacting stably with the active site. Indeed, rEpiP-S393A was shown to be impaired in its protease activity. Mice vaccinated with rEpiP were protected from S. aureus infection (34% survival, P=0.0054). Moreover, the protective efficacy generated by rEpiP and rEpiP-S393A was comparable, implying that the noncleaving mutant could be used for vaccination purposes.

Characterization of amylolysin, a novel lantibiotic from Bacillus amyloliquefaciens GA1

Background

Lantibiotics are heat-stable peptides characterized by the presence of thioether amino acid lanthionine and methyllanthionine. They are capable to inhibit the growth of Gram-positive bacteria, including Listeria monocytogenes, Staphylococcus aureus or Bacillus cereus, the causative agents of food-borne diseases or nosocomial infections. Lantibiotic biosynthetic machinery is encoded by gene cluster composed by a structural gene that codes for a pre-lantibiotic peptide and other genes involved in pre-lantibiotic modifications, regulation, export and immunity.

Methodology/Findings

Bacillus amyloliquefaciens GA1 was found to produce an antimicrobial peptide, named amylolysin, active on an array of Gram-positive bacteria, including methicillin resistant S. aureus. Genome characterization led to the identification of a putative lantibiotic gene cluster that comprises a structural gene (amlA) and genes involved in modification (amlM), transport (amlT), regulation (amlKR) and immunity (amlFE). Disruption of amlA led to loss of biological activity, confirming thus that the identified gene cluster is related to amylolysin synthesis. MALDI-TOF and LC-MS analysis on purified amylolysin demonstrated that this latter corresponds to a novel lantibiotic not described to date. The ability of amylolysin to interact invitro with the lipid II, the carrier of peptidoglycan monomers across the cytoplasmic membrane and the presence of a unique modification gene suggest that the identified peptide belongs to the group B lantibiotic. Amylolysin immunity seems to be driven by only two AmlF and AmlE proteins, which is uncommon within the Bacillus genus.

Conclusion/Significance

Apart from mersacidin produced by Bacillus amyloliquefaciens strains Y2 and HIL Y-85,544728, reports on the synthesis of type B-lantibiotic in this species are scarce. This study reports on a genetic and structural characterization of another representative of the type B lantibiotic in B. amyloliquefaciens.

Effect of bile on nisin-mediated antibacterial activity and the expression of nisin genes of Lactococcus lactis W8

The capability of Lactococcus lactis to produce nisin in the presence of bile in the intestinal environment remains an intriguing question. The aim of this study was to determine the effects of bile on production of nisin and the mRNA expression of nisin genes of L. lactis W8. The strain L. lactis W8 was grown on glucose in the absence and presence of bile (0.005-0.08 %) and the antibacterial activities of culture supernatants were determined. In culture with 0.035 % bile, the nisin activity was significantly reduced (400 AU/mL) within 5 h compared to that in the control without bile (2000 AU/mL), while growth of the cells was only slightly affected. In the presence of 0.07 % bile no nisin activity of the strain was manifested. Consistent with these results, mRNA expression of nisin-biosynthetic genes nisZ, nisRK, nisI, and nisF was down-regulated by 7.5-, 2.5-, 1.7-, and 6.0-fold, respectively in cells grown in the presence of bile (0.07 %) as compared to control culture without bile. The present study suggested that bile inhibited transcription of nisin genes. Nisin-production in intestine by orally administered L. lactis, thus, does not occur since complete inhibition of nisin-production by bile is observed at a concentration much lower than the physiological concentration (0.3 %) of bile present in the human intestine. The molecular mechanism underlying the bile-mediated inhibition of nisin genes remains to be elucidated. This is the first report on bile-mediated inhibition of nisin genes.

The First structure of a lantibiotic immunity protein, SpaI from Bacillus subtilis, reveals a novel fold

Lantibiotics are peptide-derived antibiotics that inhibit the growth of Gram-positive bacteria via interactions with lipid II and lipid II-dependent pore formation in the bacterial membrane. Due to their general mode of action the Gram-positive producer strains need to express immunity proteins (LanI proteins) for protection against their own lantibiotics. Little is known about the immunity mechanism protecting the producer strain against its own lantibiotic on the molecular level. So far, no structures have been reported for any LanI protein. We solved the structure of SpaI, a LanI protein from the subtilin producing strain Bacillus subtilis ATCC 6633. SpaI is a 16.8-kDa lipoprotein that is attached to the outside of the cytoplasmic membrane via a covalent diacylglycerol anchor. SpaI together with the ABC transporter SpaFEG protects the B. subtilis membrane from subtilin insertion. The solution-NMR structure of a 15-kDa biologically active C-terminal fragment reveals a novel fold. We also demonstrate that the first 20 N-terminal amino acids not present in this C-terminal fragment are unstructured in solution and are required for interactions with lipid membranes. Additionally, growth tests reveal that these 20 N-terminal residues are important for the immunity mediated by SpaI but most likely are not part of a possible subtilin binding site. Our findings are the first step on the way of understanding the immunity mechanism of B. subtilis in particular and of other lantibiotic producing strains in general.

Antibacterial peptides "bacteriocins": an overview of their diverse characteristics and applications

Bacteriocins are ribosomally synthesized antibacterial peptides produced by bacteria that inhibit the growth of similar or closely related bacterial strains. A number of bacteriocins from a wide variety of bacteria have been discovered, and their diverse structures have been reported. Growing evidence suggests that bacteriocins have diverse structures, modes of action, mechanisms of biosynthesis and self-immunity, and gene regulation. Bacteriocins are considered as an attractive compound in food and pharmaceutical industries to prevent food spoilage and pathogenic bacterial growth. Furthermore, elucidation of their biosynthesis has led to the use of bacteriocin-controlled gene-expression systems and the biosynthetic enzymes of lantibiotics, a class of bacteriocins, as tools to design novel peptides. In this review, we summarize and discuss currently known information on bacteriocins produced by Gram-positive bacteria and their applications.

NMR resonance assignment of the autoimmunity protein SpaI from Bacillus subtilis ATCC 6633

Bacillus subtilis ATCC 6633 produces the lipid II targeting lantibiotic subtilin. For self-protection these gram-positive bacteria express a cluster of four self-immunity proteins named SpaIFEG. SpaI is a 16.8 kDa lipoprotein which is attached to the outside of the cytoplasmic membrane via a covalently linked diacylglycerol anchor. Together with the ABC-transporter SpaFEG, SpaI protects the membrane from subtilin insertion and there is evidence for a direct interaction of SpaI with subtilin. As a prerequisite for further structural studies of SpaI and the SpaI/subtilin complex we report here the full (1)H, (15)N, (13)C chemical shift assignment for a stable 14.9 kDa C-terminal fragment of SpaI.

Gene cluster analysis for the biosynthesis of elgicins, novel lantibiotics produced by Paenibacillus elgii B69

Background

The recent increase in bacterial resistance to antibiotics has promoted the exploration of novel antibacterial materials. As a result, many researchers are undertaking work to identify new lantibiotics because of their potent antimicrobial activities. The objective of this study was to provide details of a lantibiotic-like gene cluster in Paenibacillus elgii B69 and to produce the antibacterial substances coded by this gene cluster based on culture screening.

Results

Analysis of the P. elgii B69 genome sequence revealed the presence of a lantibiotic-like gene cluster composed of five open reading frames (elgT1, elgC, elgT2, elgB, and elgA). Screening of culture extracts for active substances possessing the predicted properties of the encoded product led to the isolation of four novel peptides (elgicins AI, AII, B, and C) with a broad inhibitory spectrum. The molecular weights of these peptides were 4536, 4593, 4706, and 4820 Da, respectively. The N-terminal sequence of elgicin B was Leu-Gly-Asp-Tyr, which corresponded to the partial sequence of the peptide ElgA encoded by elgA. Edman degradation suggested that the product elgicin B is derived from ElgA. By correlating the results of electrospray ionization-mass spectrometry analyses of elgicins AI, AII, and C, these peptides are deduced to have originated from the same precursor, ElgA.

Conclusions

A novel lantibiotic-like gene cluster was shown to be present in P. elgii B69. Four new lantibiotics with a broad inhibitory spectrum were isolated, and these appear to be promising antibacterial agents.

Genes involved in immunity to and secretion of aureocin A53, an atypical class II bacteriocin produced by Staphylococcus aureus A53

Aureocin A53 is an antimicrobial peptide produced by Staphylococcus aureus A53. The genetic determinants involved in aureocin A53 production and immunity to its action are organized in at least four transcriptional units encoded by the 10.4-kb plasmid pRJ9. One transcriptional unit carries only the bacteriocin structural gene, aucA. No immunity gene is found downstream of aucA, as part of the same transcriptional unit. Further downstream of aucA is found an operon which contains the three genes aucEFG, whose products seem to associate to form a dedicated ABC transporter. When aucEFG were expressed in RN4220, an aureocin A53-sensitive S. aureus strain, this strain became partially resistant to the bacteriocin. A gene disruption mutant in aucE was defective in aureocin A53 externalization and more sensitive to aureocin A53 than the wild-type strain, showing that aucEFG are involved in immunity to aureocin A53 by active extrusion of the bacteriocin. Full resistance to aureocin A53 was exhibited by transformants carrying, besides aucEFG, the operon formed by two genes, aucIB and aucIA, located between aucA and aucEFG and carried in the opposite strand. AucIA and AucIB share similarities with hypothetical proteins not found in the gene clusters of other bacteriocins. A gene disruption mutant in orf8, located upstream of aucA and whose product exhibits about 50% similarity to a number of hypothetical membrane proteins found in many Gram-positive bacteria, was strongly affected in aureocin A53 externalization but resistant to aureocin A53, suggesting that Orf8 is also involved in aureocin A53 secretion.

Salivaricin D, a novel intrinsically trypsin-resistant lantibiotic from Streptococcus salivarius 5M6c isolated from a healthy infant

In this work, we purified and characterized a newly identified lantibiotic (salivaricin D) from Streptococcus salivarius 5M6c. Salivaricin D is a 34-amino-acid-residue peptide (3,467.55 Da); the locus of the gene encoding this peptide is a 16.5-kb DNA segment which contains genes encoding the precursor of two lantibiotics, two modification enzymes (dehydratase and cyclase), an ABC transporter, a serine-like protease, immunity proteins (lipoprotein and ABC transporters), a response regulator, and a sensor histidine kinase. The immunity gene (salI) was heterologously expressed in a sensitive indicator and provided significant protection against salivaricin D, confirming its immunity function. Salivaricin D is a naturally trypsin-resistant lantibiotic that is similar to nisin-like lantibiotics. It is a relatively broad-spectrum bacteriocin that inhibits members of many genera of Gram-positive bacteria, including the important human pathogens Streptococcus pyogenes and Streptococcus pneumoniae. Thus, Streptococcus salivarius 5M6c may be a potential biological agent for the control of oronasopharynx-colonizing streptococcal pathogens or may be used as a probiotic bacterium.

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.

Bioengineering of a Nisin A-producing Lactococcus lactis to create isogenic strains producing the natural variants Nisin F, Q and Z

Nisin is the prototypical example of the lantibiotic family of antimicrobial peptides and has been employed as a food preservative for over half a century. It has also attracted attention due to its potency against a number of multidrug‐resistant clinical pathogens. Nisin A is the originally isolated form of Nisin and a further five natural variants have been described which differ by up to 10 amino acids (of 34 in total in Nisin A). Nisins A, Z, F and Q are produced by Lactococcus lactis, while Nisins U and U2 are produced by Streptococcus sp. In this study we bioengineered the nisA gene of a Nisin A producer to generate genes encoding Nisins Z, F, Q, U and U2. We determined that while active Nisin Z, F and Q can be produced against this genetic background, active forms of Nisin U and U2 are not generated. Minimum inhibitory concentration studies with Nisin A, Z, F and Q variants against a series of different clinically significant pathogens establish differences in specific activities against selected targets. Nisin F was most impressive, being the most active, or one of the most active, against the MRSA strain ST 525, EC 676, EC 725, VISA 22900, VISA 22781, hVISA 35197, Staphylococcus aureus 8325‐4 and L. lactis HP. Nisin Z was most active against ST 299, hVISA 32683 and, together with Nisin F, HP but had contrastingly poor activity against ST 525, EC 676 and 8325‐4. Nisin F, Q and A exhibited similar potency against VISA 22900. This was the only target against which Nisin Q and Nisin A were among the most active variants.

Production and pH-Dependent Bactericidal Activity of Lactocin S, a Lantibiotic from Lactobacillus sake L45

The amount of lactocin S activity in a growing culture depends on the growth stage of the bacteria, the pH of the medium, the presence of ethanol, and the aeration of the culture. We observed the highest levels of bacteriocin activity in the early stationary growth phase of cultures at 30 deg C. When Lactobacillus sake L45 was grown in a fermentor at pH 5, it produced 2,000 to 3,000 bacteriocin units per ml, which represented an 8- to 10-fold increase in bacteriocin production compared with production during batch culture fermentation. Less than 10% of this level of bacteriocin activity was observed during fermentation at pH 6.0. When 1% ethanol was included in the growth medium, a two- to fourfold increase in the bacteriocin yield was observed. Aerating the culture during growth almost completely eliminated the production of active bacteriocin. Our results also showed that lactocin S-mediated killing of target cells depended on the pH of the culture. The pH had to be less than 6 in order to obtain a bactericidal effect with lactocin S-sensitive cells. At pH values greater than 6, lactocin S had no apparent effect on sensitive cells.

sigma(B) and sigma(L) contribute to Listeria monocytogenes 10403S response to the antimicrobial peptides SdpC and nisin

The ability of the foodborne pathogen Listeria monocytogenes to survive antimicrobial treatments is a public health concern; therefore, this study was designed to investigate genetic mechanisms contributing to antimicrobial response in L. monocytogenes. In previous studies, the putative bacteriocin immunity gene lmo2570 was predicted to be regulated by the stress responsive alternative sigma factor, sigma(B). As the alternative sigma factor sigma(L) controls expression of genes important for resistance to some antimicrobial peptides, we hypothesized roles for lmo2570, sigma(B), and sigma(L) in L. monocytogenes antimicrobial response. Results from phenotypic characterization of a L. monocytogenes lmo2570 null mutant suggested that this gene does not contribute to resistance to nisin or to SdpC, an antimicrobial peptide produced by some strains of Bacillus subtilis. While lmo2570 transcript levels were confirmed to be sigma(B) dependent, they were sigma(L) independent and were not affected by the presence of nisin under the conditions used in this study. In spot-on-lawn assays with the SdpC-producing B. subtilis EG351, the L. monocytogenes DeltasigB, DeltasigL, and DeltasigB/DeltasigL strains all showed increased sensitivity to SdpC, indicating that both sigma(B) and sigma(L) regulate genes contributing to SdpC resistance. Nisin survival assays showed that sigma(B) and sigma(L) both affect L. monocytogenes sensitivity to nisin in broth survival assays; that is, a sigB null mutant is more resistant than the parent strain to nisin, while a sigB null mutation in DeltasigL background leads to reduced nisin resistance. In summary, while the sigma(B)-dependent lmo2570 does not contribute to resistance of L. monocytogenes to nisin or SdpC, both sigma(B) and sigma(L) contribute to the L. monocytogenes antimicrobial response.

Microbial quorum sensing: a tool or a target for antimicrobial therapy?

Inter-cell communication aided by released chemical signals when cell density reaches a critical concentration has been investigated for over 30 years as quorum sensing. Originally discovered in Gram-negative bacteria, quorum-sensing systems have also been studied extensively in Gram-positive bacteria and dimorphic fungi. Microbial communities communicating via quorum sensing employ various chemical signals to supervise their surrounding environment, alter genetic expression and gain advantage over their competitors. These signals vary from acylhomoserine lactones to small modified or unmodified peptides to complex gamma-butyrolactone molecules. The scope of this review is to give an insight into some of the quorum-sensing systems now known and to explore their role in microbial physiology and development of pathogenesis. Particular attention will be dedicated to the signalling molecules involved in quorum-sensing-mediated processes and the potential shown by some of their natural and synthetic analogues in the treatment of infections triggered by quorum sensing.

Bacteriocins from Lactobacillus plantarum - production, genetic organization and mode of action: produção, organização genética e modo de ação

Bacteriocins are biologically active proteins or protein complexes that display a bactericidal mode of action towards usually closely related species. Numerous strains of bacteriocin producing Lactobacillus plantarum have been isolated in the last two decades from different ecological niches including meat, fish, fruits, vegetables, and milk and cereal products. Several of these plantaricins have been characterized and the aminoacid sequence determined. Different aspects of the mode of action, fermentation optimization and genetic organization of the bacteriocin operon have been studied. However, numerous of bacteriocins produced by different Lactobacillus plantarum strains have not been fully characterized. In this article, a brief overview of the classification, genetics, characterization, including mode of action and production optimization for bacteriocins from Lactic Acid Bacteria in general, and where appropriate, with focus on bacteriocins produced by Lactobacillus plantarum, is presented.