Production of enterocins L50A, L50B, and IT, a new enterocin, by Enterococcus faecium IT62, a strain isolated from Italian ryegrass in Japan

Evaluation of Antifungal Metabolites Produced by Lactic Acid Bacteria

This study aimed to select and characterize lactic acid bacteria (LAB) with potential antifungal activities against the filamentous fungi Alternaria alternata ATCC MYA-4642, Aspergillus flavus KACC 45470, Aspergillus niger KACC 42589, Cladosporium sphaerospermum ATCC MYA-4645, Penicillium chrysogenum ATCC MYA-4644, and Penicillium expansum KACC 40815. Initial screening of the antifungal activity has identified six LAB strains belonging to the genera Enterococcus and Leuconostoc, selected by their antagonistic activities against at least three of the filamentous fungi in the test panel. Preliminary prediction of bioactive compounds was carried out to narrow down the possible identity of the antagonistic metabolites produced by the studied LAB. Furthermore, metabolic profiles were assessed and used as a basis for the identification of key metabolites based on VIP scores and PCA plot scores. Key metabolites were identified to be β-phenyllactic acid, ⍺-hydroxyisobutyric acid, 1,3-butanediol, phenethylamine, and benzoic acid. Individual assessment of each metabolic compound against the test panel showed specificity inhibitory patterns; yet, combinations between them only showed additive, but not synergetic effects. The pH neutralization significantly reduced the antifungal activity of the cell-free supernatant (CFS), but no bioactive compounds were found to be stable in high temperatures and pressure. This study will be beneficial as an additional building block on the existing knowledge and future antifungal application of LAB produced metabolites. Furthermore, this study also provides a new bio-preservative perspective on unexplored antifungal metabolites produced by LAB as biocontrol agents.

Enterococcus spp. as a Producer and Target of Bacteriocins: A Double-Edged Sword in the Antimicrobial Resistance Crisis Context

Enterococcus spp. are one of the most frequent producers of bacteriocins (enterocins), which provides them with an advantage to compete in their natural environment, which is the gut of humans and many animals. The enterocins’ activity against microorganisms from different phylogenetic groups has raised interest in Enterococcus spp. in different contexts throughout the last decades, especially in the food industry. Nevertheless, some species can also cause opportunistic life-threatening infections and are frequently multidrug-resistant (MDR). Vancomycin-resistant Enterococcus (VRE), in particular, are an ongoing global challenge given the lack of therapeutic options. In this scenario, bacteriocins can offer a potential solution to this persistent threat, either alone or in combination with other antimicrobials. There are a handful of studies that demonstrate the advantages and applications of bacteriocins, especially against VRE. The purpose of this review is to present a current standpoint about the dual role of Enterococcus spp., from important producers to targets needed to be controlled, and the crucial role that enterocins may have in the expansion of enterococcal populations. Classification and distribution of enterocins, the current knowledge about the bacteriocinome of clinical enterococci, and the challenges of bacteriocin use in the fight against VRE infections are particularly detailed.

Tarkhineh as a new microencapsulation matrix improves the quality and sensory characteristics of probiotic Lactococcus lactis KUMS-T18 enriched potato chips

In the present study, probiotic potato chips containing a newly isolated probiotic Lactococcus lactis KUMS-T18 strain were produced by using a simple spraying method and then enhancing the stability, survival rate, and sensory characteristics of product during storage at 4 °C and 25 °C was examined for four months. Based on the results, Lactococcus lactis KUMS-T18 isolated from traditional Tarkhineh as a safe strain had high tolerance to low pH and high bile salt, anti-pathogenic activity, hydrophobicity, adhesion to human epithelial cells, auto- and co-aggregation, cholesterol assimilation and antibiotic susceptibility. Meanwhile, by micro-coating the probiotic cells in Tarkhineh formulations, elliptical to spherical shape (460-740 µm) probiotic drops were produced. The results revealed that potato chips produced with turmeric and plain Tarkhineh during storage at 4 °C, had excellent protection abilities for probiotic cells with about 4.52 and 3.46 log decreases in CFU/g respectively. On the other hand, probiotic potato chips, compared to non-probiotic and commercial potato chips, showed the criteria of probiotic products such as excellent quality and superior sensory characteristics. In summary, this study proved that probiotic Lactococcus lactis KUMS-T18 strain covered by Tarkhineh formulations as protective matrix has high potential to be used in the production of probiotic potato chips.

Characterization of Partially Purified Bacteriocins Produced by Enterococcus faecium Strains Isolated from Soybean Paste Active Against Listeria spp. and Vancomycin-Resistant Enterococci

Three out of one hundred eighty putative LAB isolates from Korean traditional fermented soybean paste were identified to be unique and bacteriocinogenic strains. Based on phenotypic and 16S rRNA sequencing analysis, selected strains were identified as Enterococcus faecium ST651ea, E. faecium ST7119ea and E. faecium ST7319ea. The bacteriocinogenic properties of the studied strains were evaluated against Listeria monocytogenes ATCC15313, Listeria innocua ATCC33090 and vancomycin-resistant E. faecium VRE19 of clinical origin. The strains E. faecium ST651ea, ST7119ea and ST7319ea expressed bacteriocins with an activity of 12,800 AU/mL, 25,600 AU/mL and 25,600 AU/mL, respectively, recorded against L. monocytogenes ATCC15131. According to the PCR-based screening of bacteriocin-related genes, which was further confirmed through amplicon sequencing, showed that strain E. faecium ST651ea carries entB and entP genes, whereas both E. faecium ST7119ea and ST7319ea strains harbor entA and entB genes. The molecular size of expressed bacteriocins was estimated by tricine-SDS-PAGE showing an approximative protein size of 4.5 kDa. The assessment of the spectrum of activity of bacteriocins ST651ea, ST7119ea and ST7319ea showed strong activity against most of clinical VRE isolates, majority of other Enterococcus spp. and Listeria spp. Bacteriocins ST651ea, ST7119ea and ST7319ea were partially purified by combination of 60% ammonium sulfate precipitation and hydrophobic chromatography on the SepPakC₁₈ column. Challenge test with semi-purified (60% 2-propanol fraction) bacteriocins resulted in a significant reduction of viable cells for all test organisms. Thus, indicating that all the bacteriocins evaluated can be used as potential biocontrol in food and feed industries as well as an alternative treatment for VRE-related infections in both veterinary and clinical settings.

Application of Tarkhineh Fermented Product to Produce Potato Chips With Strong Probiotic Properties, High Shelf-Life, and Desirable Sensory Characteristics

The application of Tarkhineh texture to protect probiotics in potato chips has been investigated as the main goal in this paper. In this study, the probiotic assessments, morphological characteristics, sensory evaluation, and survival rates of the covered probiotic cells with Tarkhineh in potato chips during storage time were assessed. Based on results, T34 isolated from traditional Tarkhineh as a safe strain had a high tolerance to low pH and bile salt conditions, displayed acceptable anti-pathogenic activities, and also showed desirable antibiotic susceptibility. Two types of Tarkhineh formulations (plain Tarkhineh and turmeric Tarkhineh) were applied using a simple spraying method for covering T34 cells in potato chips. All formulations showed elliptical to spherical (480-770 μm) shape probiotic drops. Storage stability results revealed that T34 cells mixed with turmeric and plain Tarkhineh during 4 months of storage at 4°C displayed excellent protection abilities with about 3.70 and 2.85 log decreases in CFU/g respectively. Additionally, probiotic potato chips compared to non-probiotic and commercial potato chips, exhibited probiotic product criteria such as excellent quality and superior sensory properties during storage time. In conclusion, Tarkhineh showed high potential as a protective matrix for probiotic cells in potato chips.

Identification of punicalagin as the bioactive compound behind the antimicrobial activity of pomegranate (Punica granatum L.) peels

Extracts from 'Zhéri' and 'Hicaznar' varieties of pomegranate, Punica granatum L., were obtained by subjecting powdered peels to extraction using water, water/ethanol (1:1; v/v), ethanol, acetone and heptane. Using the agar diffusion assay, extracts with water and/or ethanol were shown to display significant antimicrobial activity with diameters of inhibition zones up to 20 mm. Ethanolic extracts, which were the most active, were fractionated using SPE, HPLC and UHPLC, and the active compounds they contain were identified by mass spectrometry. Punicalagin, under its α and β anomeric forms, was identified as the antibacterial compound in pomegranate peel extracts. Both forms were active with MIC values between 0.3 and 1.2 µg.ml^-1, and they easily converted from one to the other with an α/β equilibrium ratio of 3/7. Their spectrum of activity targeted 10 out of 13 Gram positive and two out of three Gram negative bacteria as well as a yeast strain.

Bacteriocin production and distribution of bacteriocin-encoding genes in enterococci from dogs

Many enterococcal strains produce bacteriocins, which could be useful as natural food preservatives through inhibition of pathogenic and spoilage microorganisms. There is little knowledge of the distribution and spectrum of bacteriocin activity and the distribution of bacteriocin-encoding genes in enterococci isolated from dogs. Therefore, we subjected 160 enterococcal isolates (E. faecium n=92, E. faecalis n=35, E. hirae n=28, E. casseliflavus n=3, E. mundtii n=2) from 105 samples of dog faeces to polymerase chain reaction (PCR) detection of genes for enterocin A, P, B, L50A, L50B, AS-48, and bac31 and to screening for bacteriocin activity. The results showed the presence of at least one of the tested genes in 54/160 isolates, with E. faecium the most common gene-possessing species. The most frequently occurring gene for production of enterocin A was observed in combination with enterocin P and B. Bacteriocin activity was observed in 76/160 isolates against at least one of 5 indicator bacteria from the genus Listeria, Enterococcus, Streptococcus and Staphylococcus. Four selected strains (IK25, Bri, I/Dz, P10) were active mostly against different species of Enterococcus (in the range 400-25 600 AU/mL) and Listeria sp. (800-12 800 AU/mL) but no Gram-negative bacteria were inhibited. Protein character, thermostability (up to 121°C) and stability at different pH values (3.0-10.0) were confirmed for crude bacteriocins of these four strains. The antimicrobial substance of E. faecium IK25 strain was identified as enterocin B using molecular weight detection and the presence of genes.

Pathogenicity characteristics of Enterococcus faecium from diseased black bears

The death of several black bears at the black bear breeding base in Yunnan Pingbian Daweishan is a matter of concern. Multiple black bears exhibited decreased appetite or unusual waste, and some were soporific or suffered from vomiting and anhelation. In order to ascertain the cause of death, 16S rDNA gene sequencing and phylogenetic analysis was performed on bacteria isolated from tissue samples obtained from dead bears. The biochemical characteristics of the isolated bacteria were subsequently analyzed using different biochemical test systems. The bacteria can decompose glucose, but it cannot produce gas. The fermentation study of sucrose, lactose, trehalose, glycerol and mannitol yielded positive results; while it was unable to decompose urea or ODC (ornithine decarboxylase). Basic Local Alignment Search Tool (BLAST) analysis of a ~1500-bp DNA product amplified from the 16S rDNA of the bacterial isolate revealed that Enterococcus faecium from black bears is highly similar to other E. faecium isolates in the National Center for Biotechnology Information (NCBI) database, and the highest sequence similarity (99%) was with the reference strain. In addition, mice infected with the E. faecium isolate succumbed to severe damage to the lungs, liver, spleen, myocardium, and kidney tissues. In summary, the isolated E. faecium from dead black bears induced pathological changes in mice.

Bacteriocin-Producing Enterococcus faecium LCW 44: A High Potential Probiotic Candidate from Raw Camel Milk

Bacterial isolates from raw camel milk were screened for antibacterial activity using the agar diffusion assay. Ten isolates selected for their inhibition of Gram-positive bacteria were identified by 16S sequencing as Enterococcus faecium or durans. An isolate named E. faecium LCW 44 exhibited the broadest antibacterial spectrum with an inhibitory activity against several Gram-positive strains belonging to the genera Clostridium, Listeria, Staphylococcus, and Lactobacillus. E. faecium LCW 44 was shown to produce N-formylated enterocins L50A and L50B, as revealed by mass spectrometry and PCR analyses. This isolate did not harbor any of the virulence factors tested and was shown to be sensitive to all tested antibiotics. It showed high resistance to gastric and intestinal conditions (78 ± 4% survival). Its adhesion index was evaluated at 176 ± 86 and 24 ± 86 on Caco-2 cells and HT-29 cells, respectively, and it significantly reduced adhesion of Listeria monocytogenes by 65 and 49%, respectively. In Macfarlane broth (simulating the nutrient content of the colon), counts of L. monocytogenes were reduced by 2 log₁₀ cycles after 24 h in co-culture with E. faecium LCW 44, compared to the increase of 4 log₁₀ cycles when cultured alone. Comparison with a bacteriocin-non-producing mutant of E. faecium LCW 44 strongly suggests that inhibition of L. monocytogenes was due to bacteriocin production. Altogether, E. faecium LCW 44 thus has potential for use as a probiotic for humans and veterinary medicine.

Nutrition-adaptive control of multiple-bacteriocin production by Weissella hellenica QU 13

AIM

To analyse nutrition-adaptive multiple-bacteriocin production by Weissella hellenica QU 13.

METHODS AND RESULTS

Weissella hellenica QU 13 produces two leaderless bacteriocins, weissellicins Y and M. Their production was studied in MRS and APT media by quantification analyses with liquid chromatography mass spectrometry (LC/MS), while transcriptional analysis of biosynthetic genes was performed by real-time reverse transcription (RT)-PCR. Weissellicin Y production was higher in MRS culture than in APT culture, while weissellicin M production was higher in APT culture than in MRS culture. APT medium contains a higher amount of thiamine than MRS medium, to enhance the growth of heterofermentative lactic acid bacteria. Therefore, thiamine addition to MRS culture enhanced the growth of W. hellenica QU 13; consequently, weissellicin Y production was decreased, while weissellicin M production was not affected. Furthermore, real-time RT-PCR analyses indicated that the transcriptional trends of their respective structural genes, welY and welM, were different from each other, and that these two genes' transcriptions responded to nutrition conditions.

CONCLUSION

Weissella hellenica QU 13 was demonstrated to control weissellicins Y and M production based on nutrition conditions. In addition, differential expression behaviour of weissellicins Y and M indicates that each of them would have separate roles to adapt to different environmental situations.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report that describes nutrition-adaptive multiple-bacteriocin production, in which thiamine inhibits bacteriocin production while it enhances the growth of the producer strain.

Maltaricin CPN, a new class IIa bacteriocin produced by Carnobacterium maltaromaticum CPN isolated from mould-ripened cheese

AIMS

The purpose of this study was to isolate, characterize and determine the structure and the antibacterial activities of a bacteriocin produced by Carnobacterium maltaromaticum CPN, a strain isolated from unpasteurized milk Camembert cheese.

METHODS AND RESULTS

This bacteriocin, termed maltaricin CPN, was produced at higher amounts in MRS broth at temperatures between 15°C and 25°C. It was purified to homogeneity from culture supernatant by using a simple method consisting of cation-exchange and reversed-phase chromatographies. Mass spectrometry showed that maltaricin was a 4427·29 Da bacteriocin. Its amino acid sequence was determined by Edman degradation which showed that it had close similarity with bacteriocins of the class IIa. Maltaricin CPN consisted in fact of 44 unmodified amino acids including two cysteine residues at positions 9 and 14 linked by a disulphide bond. The antimicrobial activity of maltaricin CPN covered a range of bacteria, with strong activity against many species of Gram-positive bacteria, especially the food-borne pathogen Listeria monocytogenes, but no activity against Gram-negative ones.

CONCLUSIONS

In the studied conditions, C. maltaromaticum CPN produced a new class IIa bacteriocin with strong anti-Listeria activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study covers the purification and the structural characterization of a new bacteriocin produced by strain C. maltaromaticum CPN isolated from Camembert cheese. Its activity against strains of L. monocytogenes and higher production rates at relatively low temperatures show potential technological applications to improve the safety of refrigerated food.

Bacteriocins: Novel Solutions to Age Old Spore-Related Problems?

Bacteriocins are ribosomally synthesized antimicrobial peptides produced by bacteria, which have the ability to kill or inhibit other bacteria. Many bacteriocins are produced by food grade lactic acid bacteria (LAB). Indeed, the prototypic bacteriocin, nisin, is produced by Lactococcus lactis, and is licensed in over 50 countries. With consumers becoming more concerned about the levels of chemical preservatives present in food, bacteriocins offer an alternative, more natural approach, while ensuring both food safety and product shelf life. Bacteriocins also show additive/synergistic effects when used in combination with other treatments, such as heating, high pressure, organic compounds, and as part of food packaging. These features are particularly attractive from the perspective of controlling sporeforming bacteria. Bacterial spores are common contaminants of food products, and their outgrowth may cause food spoilage or food-borne illness. They are of particular concern to the food industry due to their thermal and chemical resistance in their dormant state. However, when spores germinate they lose the majority of their resistance traits, making them susceptible to a variety of food processing treatments. Bacteriocins represent one potential treatment as they may inhibit spores in the post-germination/outgrowth phase of the spore cycle. Spore eradication and control in food is critical, as they are able to spoil and in certain cases compromise the safety of food by producing dangerous toxins. Thus, understanding the mechanisms by which bacteriocins exert their sporostatic/sporicidal activity against bacterial spores will ultimately facilitate their optimal use in food. This review will focus on the use of bacteriocins alone, or in combination with other innovative processing methods to control spores in food, the current knowledge and gaps therein with regard to bacteriocin-spore interactions and discuss future research approaches to enable spores to be more effectively targeted by bacteriocins in food settings.

Gene cluster responsible for secretion of and immunity to multiple bacteriocins, the NKR-5-3 enterocins

Enterococcus faecium NKR-5-3, isolated from Thai fermented fish, is characterized by the unique ability to produce five bacteriocins, namely, enterocins NKR-5-3A, -B, -C, -D, and -Z (Ent53A, Ent53B, Ent53C, Ent53D, and Ent53Z). Genetic analysis with a genome library revealed that the bacteriocin structural genes (enkA [ent53A], enkC [ent53C], enkD [ent53D], and enkZ [ent53Z]) that encode these peptides (except for Ent53B) are located in close proximity to each other. This NKR-5-3ACDZ (Ent53ACDZ) enterocin gene cluster (approximately 13 kb long) includes certain bacteriocin biosynthetic genes such as an ABC transporter gene (enkT), two immunity genes (enkIaz and enkIc), a response regulator (enkR), and a histidine protein kinase (enkK). Heterologous-expression studies of enkT and ΔenkT mutant strains showed that enkT is responsible for the secretion of Ent53A, Ent53C, Ent53D, and Ent53Z, suggesting that EnkT is a wide-range ABC transporter that contributes to the effective production of these bacteriocins. In addition, EnkIaz and EnkIc were found to confer self-immunity to the respective bacteriocins. Furthermore, bacteriocin induction assays performed with the ΔenkRK mutant strain showed that EnkR and EnkK are regulatory proteins responsible for bacteriocin production and that, together with Ent53D, they constitute a three-component regulatory system. Thus, the Ent53ACDZ gene cluster is essential for the biosynthesis and regulation of NKR-5-3 enterocins, and this is, to our knowledge, the first report that demonstrates the secretion of multiple bacteriocins by an ABC transporter.

Purification and characterization of enterocin MC13 produced by a potential aquaculture probiontEnterococcus faeciumMC13 isolated from the gut ofMugil cephalus

A bacteriocin producer strain MC13 was isolated from the gut of Mugil cephalus (grey mullet) and identified as Enterococcus faecium . The bacteriocin of E. faecium MC13 was purified to homogeneity, as confirmed by Tricine sodium dodecyl sulphate – polyacrylamide gel electrophoresis (SDS–PAGE). Reverse-phase high-performance liquid chromatography (HPLC) analysis showed a single active fraction eluted at 26 min, and matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry analysis showed the molecular mass to be 2.148 kDa. The clear zone in native PAGE corresponding to enterocin MC13 band further substantiated its molecular mass. A dialyzed sample (semicrude preparation) of enterocin MC13 was broad spectrum in its action and inhibited important seafood-borne pathogens: Listeria monocytogenes , Vibrio parahaemolyticus , and Vibrio vulnificus . This antibacterial substance was sensitive to proteolytic enzymes: trypsin, protease, and chymotrypsin but insensitive to catalase and lipase, confirming that inhibition was due to the proteinaceous molecule, i.e., bacteriocin, and not due to hydrogen peroxide. Enterocin MC13 tolerated heat treatment (up to 90 °C for 20 min). Enterococcus faecium MC13 was effective in bile salt tolerance, acid tolerance, and adhesion to the HT-29 cell line. These properties reveal the potential of E. faecium MC13 to be a probiotic bacterium. Enterococcus faecium MC13 could be used as potential fish probiotic against pathogens such as V. parahaemolyticus, Vibrio harveyi , and Aeromonas hydrophila in fisheries. Also, this could be a valuable seafood biopreservative against L. monocytogenes.

Characterization and identification of weissellicin Y and weissellicin M, novel bacteriocins produced by Weissella hellenica QU 13

AIMS

To identify and characterize novel bacteriocins from Weissella hellenica QU 13.

METHODS AND RESULTS

Weissella hellenica QU 13, isolated from a barrel used to make Japanese pickles, produced two novel bacteriocins termed weissellicin Y and weissellicin M. The primary structures of weissellicins Y and M were determined, and their molecular masses were determined to be 4925·12 and 4968·40 Da, respectively. Analysis of the DNA sequence encoding the bacteriocins revealed that they were synthesized and secreted without N-terminal extensions such as leader sequences or sec signal peptides. Weissellicin M showed significantly high and characteristic homology with enterocins L50A and L50B, produced by Enterococcus faecium L50, while weissellicin Y showed no homology with any other known bacteriocins. Both bacteriocins showed broad antimicrobial spectra, with especially high antimicrobial activity against species, which contaminate pickles, such as Bacillus coagulans, and weissellicin M showed relatively higher activity than weissellicin Y. Furthermore, the stability of weissellicin M against pH and heat was distinctively higher than that of weissellicin Y.

CONCLUSIONS

Weissella hellenica QU 13 produced two novel leaderless bacteriocins, weissellicin Y and weissellicin M, and weissellicin M exhibited remarkable potency that could be employed by pickle-producing industry.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is the first report, which represents a complete identification and characterization of novel leaderless bacteriocins from Weissella genus.

Identification of an N-terminal formylated, two-peptide bacteriocin from Enterococcus faecalis 710C

Enterococcus faecalis 710C, isolated from beef product, has a broad antimicrobial activity spectrum against foodborne pathogens. Two bacteriocins, enterocin 7A (Ent7A) and enterocin 7B (Ent7B), were purified from the culture supernatant of E. faecalis 710C and characterized using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry and electrospray infusion tandem mass spectrometry analyses. These data and subsequent genetic analysis showed that Ent7A and Ent7B are produced without N-terminal leader sequences and have amino acid sequences that are identical to those of enterocins MR10A and MR10B, respectively. However, the observed masses for Ent7A and Ent7B are 5200.80 and 5206.65 Da (monoisotopic mass), respectively, which are higher than the theoretical molecular masses of MR10A and MR10B, respectively. This study provides evidence that both Ent7A and Ent7B are formylated on the N-terminal methionine residue. Purified Ent7A and Ent7B are active against spoilage microorganisms and foodborne pathogens, including Clostridium sporogenes , Listeria monocytogenes , and Staphylococcus aureus as well as Brevundimonas diminuta , which has been associated with infections among immune-suppressed cancer patients.

Biochemical characterization of a bacteriocin-like inhibitory substance produced by Enterococcus faecium MXVK29, isolated from Mexican traditional sausage

BACKGROUND

Enterococci are lactic acid bacteria that can produce bacteriocins, which may offer an additional hurdle to control the growth of food-borne pathogens; moreover, these bacteriocins may have great potential as natural biopreservatives. The aim of this work was to characterize a bacteriocin-like inhibitory substance (BLIS) with antilisterial activity produced by an enterococcal strain.

RESULTS

The bacteriogenic strain was isolated from Mexican fermented sausages and identified as Enterococcus faecium with 99% sequence similarity. Maximal activity was detected at 16 h, where bacterial growth was in middle of the stationary phase. The producer strain was not inhibited by its own antimicrobial peptide. BLIS showed a strong anti-Listeria activity and was inactivated by proteinase K. Heating (121 °C for 15 min) induced some inactivation, but thermotolerance was higher at acid pH values. The yield obtained with a pH-mediated purification process was 32.7%, showing a band with an estimated molecular weight of 3.5 kDa. Automated N-terminal Edman degradation showed the following sequence: YYGNGVTCGSHHCSVD.

CONCLUSION

Biochemical characteristics of BLIS produced by E. faecium MXVK29 suggested that it belongs to Class IIa of the Klaenhammer classification and could be considered as a natural food preservative, although further studies need to be performed.

Enterocin 96, a novel class II bacteriocin produced by Enterococcus faecalis WHE 96, isolated from Munster cheese

Enterococcus faecalis WHE 96, a strain isolated from soft cheese based on its anti-Listeria activity, produced a 5,494-Da bacteriocin that was purified to homogeneity by ultrafiltration and cation-exchange and reversed-phase chromatographies. The amino acid sequence of this bacteriocin, named enterocin 96, was determined by Edman degradation, and its structural gene was sequenced, revealing a double-glycine leader peptide. After a comparison with other bacteriocins, it was shown that enterocin 96 was a new class II bacteriocin that showed very little similarity with known structures. Enterocin 96 was indeed a new bacteriocin belonging to class II bacteriocins. The activity spectrum of enterocin 96 covered a wide range of bacteria, with strong activity against most gram-positive strains but very little or no activity against gram-negative strains.

Genetic identification of the bacteriocins produced by Enterococcus faecium IT62 and evidence that bacteriocin 32 is identical to enterocin IT

Enterococcus faecium IT62, a strain isolated from ryegrass in Japan, produces three bacteriocins (enterocins L50A, L50B, and IT) that have been previously purified and the primary structures of which have been determined by amino acid sequencing (E. Izquierdo, A. Bednarczyk, C. Schaeffer, Y. Cai, E. Marchioni, A. Van Dorsselaer, and S. Ennahar, Antimicrob. Agents Chemother., 52:1917-1923, 2008). Genetic analysis showed that the bacteriocins of E. faecium IT62 are plasmid encoded, but with the structural genes specifying enterocin L50A and enterocin L50B being carried by a plasmid (pTAB1) that is separate from the one (pTIT1) carrying the structural gene of enterocin IT. Sequencing analysis of a 1,475-bp region from pTAB1 identified two consecutive open reading frames corresponding, with the exception of 2 bp, to the genes entL50A and entL50B, encoding EntL50A and EntL50B, respectively. Both bacteriocins are synthesized without N-terminal leader sequences. Genetic analysis of a sequenced 1,380-bp pTIT1 fragment showed that the genes entIT and entIM, encoding enterocin IT and its immunity protein, respectively, were both found in E. faecium VRE200 for bacteriocin 32. Enterocin IT, a 6,390-Da peptide made up of 54 amino acids, has been previously shown to be identical to the C-terminal part of bacteriocin 32, a 7,998-Da bacteriocin produced by E. faecium VRE200 whose structure was deduced from its structural gene (T. Inoue, H. Tomita, and Y. Ike, Antimicrob. Agents Chemother., 50:1202-1212, 2006). By combining the biochemical and genetic data on enterocin IT, it was concluded that bacteriocin 32 is in fact identical to enterocin IT, both being encoded by the same plasmid-borne gene, and that the N-terminal leader peptide for this bacteriocin is 35 amino acids long and not 19 amino acids long as previously reported.

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

A segregationally stable expression and secretion vector for Saccharomyces cerevisiae, named pYABD01, was constructed by cloning the yeast gene region encoding the mating pheromone alpha-factor 1 secretion signal (MFalpha1(s)) into the S. cerevisiae high-copy-number expression vector pYES2. The structural genes of the two leaderless peptides of enterocin L50 (EntL50A and EntL50B) from Enterococcus faecium L50 were cloned, separately (entL50A or entL50B) and together (entL50AB), into pYABD01 under the control of the galactose-inducible promoter P(GAL1). The generation of recombinant S. cerevisiae strains heterologously expressing and secreting biologically active EntL50A and EntL50B demonstrates the suitability of the MFalpha1(s)-containing vector pYABD01 to direct processing and secretion of these antimicrobial peptides through the S. cerevisiae Sec system.