Purification and characterization of a novel plantaricin, KL-1Y, from Lactobacillus plantarum KL-1

Lactic Acid Bacteria isolated from traditional and innovative alheiras as potential biocontrol agents

From a selection of seven traditional and 14 innovative alheiras, 491 lactic acid bacteria (LAB) were isolated and tested for their antimicrobial activity against several food-borne pathogens. Among these, six strains revealed antimicrobial activity through potential bacteriocin production against 14 Listeria monocytogenes strains, Enterococcus faecalis ATCC 29212, Clostridium sporogenes ESB050, and Clostridium perfringens ESB054. Through whole genome sequencing (WGS), these strains were identified as Lactiplantibacillus plantarum (2), Leuconostoc mesenteroides (1), and Pediococcus acidilactici (3). Furthermore, several orthologues of class II bacteriocins genes were identified, including Plantaricin E, Plantaricin F, Pediocin PA, Enterocin X, Leucocin A, and Coagulin A. No virulence or antibiotic resistance genes' orthologues were detected by WGS analysis. However, the selected LAB strains showed variable phenotypic patterns related to virulence genes and antibiotic resistance when assessed through classical methodologies. None of these strains demonstrated the production of biogenic amines, gelatinase or DNase. Additionally, no hemolytic activity or lipase enzyme production was observed. However, only Lpb. plantarum 9A3 was sensitive to all tested antibiotics and was thus chosen for further examination. The bacteriocins produced by Lpb. plantarum (9A3) exhibited stability across a broad range of conditions, including temperatures from 4 to 100 °C, pH values ranging from 2 to 8, exposure to surfactants and detergents (Tween 20 and 80, SDS, EDTA 0.1, 2 and 5 mM, urea and sodium deoxycholate), and enzymes (papain and catalase). Their maximum activity (AU/mL = 12,800) against four L. monocytogenes strains was observed between 21 and 36 h of growth of Lbp. plantarum 9A3, indicating a bacteriostatic mode of action. Therefore, this strain appears to be a robust candidate for potential application as a protective strain to be used in the food industry. Not only is it safe, but it also produces stable bacteriocins (harbouring genes encoding for the production of three) effectively inhibiting significant pathogens such as L. monocytogenes and C. perfringens.

Mechanism of Cell-Killing Activity of Plantaricin LD1 Against Escherichia coli ATCC 25922

Plantaricin LD1 was purified from a potential probiotic strain, Lactobacillus plantarum LD1 previously isolated from indigenous food, Dosa. In this study, we have performed a detailed mechanism of action of plantaricin LD1 against Escherichia coli ATCC 25922 considering Micrococcus luteus MTCC 106 as control. The plantaricin LD1 showed a minimum inhibitory concentration (MIC) of 34.57 µg/mL and a minimum bactericidal concentration (MBC) of 138.3 µg/mL against M. luteus MTCC 106, whereas MIC 69.15 µg/mL and MBC 276.6 µg/mL were found against E. coli ATCC 25922. The efflux of potassium ions, dissipation of membrane potential (∆ψ), and transmembrane pH gradient (∆pH) of plantaricin LD1-treated cells suggested the membrane-acting nature of plantaricin LD1. Plantaricin LD1 also caused degradation of the genomic DNA of the target strains tested. The cell killing was confirmed by staining with propidium iodide and visualized under light and electron microscopes. The bacteriocin-treated cells were found to be ruptured, swollen, and elongated. Thus, the findings indicate plantaricin LD1 kills E. coli ATCC 25922 by interacting with the cell membrane resulting in the efflux of intracellular contents and also causing degradation of nucleic acids leading to cell death.

Putative Role of Anti-microbial Peptide Recovered from Lactiplantibacillus spp. in Biocontrol Activity

Antimicrobial peptides (AMPs) stand as a promising alternative to conventional pesticides, leveraging a multifaceted approach to combat plant pathogens. This study focuses on identifying and characterizing the AMP produced by Lactiplantibacillus argentoratensis strain IT, demonstrating potent antibacterial activity against various harmful microorganisms. Evaluation of AMPs' antibacterial activity was conducted through an agar well diffusion assay, a reliable method for assessing secondary metabolite antimicrobial efficacy. The study unveils the antimicrobial potential of the purified extract obtained from Lactiplantibacillus argentoratensis IT, isolated from goat milk. Notably, the AMP exhibited robust antibacterial activity against phytopathogens affecting solanaceous crops, including the Gram-negative Ralstonia solanacearum. Expression conditions and purification methods were optimized to identify the peptide's mass and sequence, utilizing LC-MS and SDS-PAGE. This paper underscores the application potential of Lactiplantibacillus spp. IT as a biocontrol agent for managing bacterial infectious diseases in plants. Results indicate optimal AMP production at 37 °C, with a culture broth pH of 5 during fermentation. The obtained peptide sequence corresponded to peaks at 842.5 and 2866.4 m/z ratio, with a molecular weight of approximately 5 kDa according to tricine SDS-PAGE analysis. In conclusion, this study lays the foundation for utilizing Lactiplantibacillus spp. IT derived AMPs in plant biocontrol strategies, showcasing their efficacy against bacterial phytopathogens. These findings contribute valuable insights for advancing sustainable agricultural practices.

Purification and characterization of Lactobacillus plantarum-derived bacteriocin with activity against Staphylococcus argenteus planktonic cells and biofilm

Bacteriocins inhibit various foodborne bacteria in planktonic and biofilm forms. However, bacteriocins with antibacterial and antibiofilm activity against Staphylococcus argenteus, a pathogen that can cause food poisoning, are still poorly known. Here, the novel bacteriocin LSB1 derived from Lactobacillus plantarum CGMCC 1.12934 was purified and characterized extensively. LSB1 had a molecular weight of 1425.78 Da and an amino acid sequence of YIFVTGGVVSSLGK. Moreover, LSB1 exhibited excellent stability under heat and acid-base stress and presented sensitivity to pepsin and proteinase K. LSB1 exhibited an extensive antimicrobial spectrum against both Gram-positive and Gram-negative bacteria. Minimum inhibitory concentration of LSB1 against S. argenteus_70917 was 10.36 µg/ml, which was lower than that of most of the previously found bacteriocins against Staphylococcus strains. Furthermore, LSB1 significantly inhibited S. argenteus_70917 planktonic cells (p < 0.01) and decreased their viability. Scanning electron microscopy analysis revealed that cell membrane permeability of S. argenteus_70917 upon exposure to LSB1 showed leakage of cytoplasmic contents and rupture, leading to cell death. In addition, biofilm formation ability of S. argenteus_70917 was significantly (p < 0.01) impaired by LSB1, with the percent inhibition of 35% at 10 µg/ml and 80% at 20 µg/ml. Overall, this study indicates that LSB1 can be considered a potential antibacterial agent in the control of S. argenteus in both planktonic and biofilm states. PRACTICAL APPLICATION: Foodborne pathogenic bacteria, such as Staphylococcus argenteus, and their biofilms represent potential risks for food safety. In recent years, customers' demand for "natural" products has increased food control. This study describes the novel bacteriocin LSB1 produced by the lactic acid bacterium species Lactobacillus plantarum. LSB1 showed strong antibacterial and antibiofilm activity against S. argenteus as well as thermal and acid-alkaline stability. Furthermore, the mechanisms of action of LSB1 on S. argenteus were preliminarily explored. These results indicate that LSB1 might be potentially used as an effective and natural food preservative.

Bacteriocins from lactic acid bacteria: purification strategies and applications in food and medical industries: a review

Background

Bacteriocins are generally defined as ribosomally synthesized peptides, which are produced by lactic acid bacteria (LAB) that affect the growth of related or unrelated microorganisms. Conventionally, the extracted bacteriocins are purified by precipitation, where ammonium sulphate is added to precipitate out the protein from the solution.

Main text

To achieve the high purity of bacteriocins, a combination with chromatography is used where the hydrophobicity and cationic properties of bacteriocins are employed. The complexity column inside the chromatography can afford to resolve the loss of bacteriocins during the ammonium sulphate precipitation. Recently, an aqueous two-phase system (ATPS) has been widely used in bacteriocins purification due to the several advantages of its operational simplicity, mild process conditions and versatility. It reduces the operation steps and processing time yet provides high recovery products which provide alternative ways to conventional methods in downstream processing. Bacteriocins are widely approached in the food and medical industry. In food application, nisin, which is produced by Lactococcus lactis subsp. has been introduced as food preservative due to its natural, toxicology safe and effective against the gram-positive bacteria. Besides, bacteriocins provide a board range in medical industries where they are used as antibiotics and probiotics.

Short conclusion

In summary, this review focuses on the downstream separation of bacteriocins from various sources using both conventional and recent ATPS techniques. Finally, recommendations for future interesting areas of research that need to be pursued are highlighted.

Synergistic Inhibition of Plantaricin E/F and Lactic Acid Against Aeromonas hydrophila LPL-1 Reveals the Novel Potential of Class IIb Bacteriocin

Plantaricin E/F (PlnEF) is a pair of two-component class IIb bacteriocin produced by lactic acid bacteria. PlnEF commonly displays potent antimicrobial activity against certain Gram-positive organisms. In this study, we investigated the synergistic activity of PlnEF combined with lactic acid against Gram-negative food and aquaculture potential pathogen Aeromonas hydrophila LPL-1, which is naturally resistant to PlnEF. We applied SDS-PAGE, wavelength-scanning, laser confocal microscopy, flow cytometer, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and two-dimensional electrophoresis to investigate their synergistic inhibitory activities. The results showed that L-lactic acid drove the release of LPS from A. hydrophila, making it possible for PlnEF to contact the inner cell membrane of A. hydrophila. Besides, co-treatment of lactic acid and PlnEF caused severe morphological and intracellular changes of A. hydrophila, including blebs on the cell surface, abnormal cell elongation, inner membrane disruption, pore-forming through the outer and inner membrane, coagulation of the cytoplasm, and structural transformation of DNA. Protein profile analysis revealed that combined treatment of lactic acid and PlnEF inhibited the energy metabolism, protein synthesis, protein folding, and DNA replication in A. hydrophila. These findings proved that PlnEF combined with lactic acid was efficient against A. hydrophila and shed light on bacteriocin’s potential and a new inhibition mechanism against A. hydrophila.

Bioprospecting Antimicrobials from Lactiplantibacillus plantarum: Key Factors Underlying Its Probiotic Action

Lactiplantibacillus plantarum (L. plantarum) is a well-studied and versatile species of lactobacilli. It is found in several niches, including human mucosal surfaces, and it is largely employed in the food industry and boasts a millenary tradition of safe use, sharing a long-lasting relationship with humans. L. plantarum is generally recognised as safe and exhibits a strong probiotic character, so that several strains are commercialised as health-promoting supplements and functional food products. For these reasons, L. plantarum represents a valuable model to gain insight into the nature and mechanisms of antimicrobials as key factors underlying the probiotic action of health-promoting microbes. Probiotic antimicrobials can inhibit the growth of pathogens in the gut ensuring the intestinal homeostasis and contributing to the host health. Furthermore, they may be attractive alternatives to conventional antibiotics, holding potential in several biomedical applications. The aim of this review is to investigate the most relevant papers published in the last ten years, bioprospecting the antimicrobial activity of characterised probiotic L. plantarum strains. Specifically, it focuses on the different chemical nature, the action spectra and the mechanisms underlying the bioactivity of their antibacterial and antiviral agents. Emerging trends in postbiotics, some in vivo applications of L. plantarum antimicrobials, including strengths and limitations of their therapeutic potential, are addressed and discussed.

Isolation, identification, and impact on intestinal barrier integrity of Lactiplantibacillus plantarum from fresh tea leaves (Camellia sinensis)

Lactic acid bacteria (LAB) are safe microorganisms that have been used in the processing of fermented food for centuries. The aim of this study was to isolate Lactobacillus from fresh tea leaves and examine the impact of an isolated strain on intestinal barrier integrity. First, the presence of Lactobacillus strains was investigated in fresh tea leaves from Kagoshima, Japan. Strains were isolated by growing on De Man, Rogosa and Sharpe (MRS) agar medium containing sodium carbonate, followed by the identification of one strain by polymerase chain reaction (PCR) and pheS sequence analysis, with the strain identified as Lactiplantibacillus plantarum and named L. plantarum LOC1. Second, the impact of strain LOC1 in its heat-inactivated form on intestinal barrier integrity was investigated. Strain LOC1, but not L. plantarum ATCC 14917^T or L. plantarum ATCC 8014, significantly suppressed dextran sulfate sodium (DSS)-induced decreases in transepithelial electrical resistance values of Caco-2:HT29-MTX 100:0 and 90:10 co-cultures. Moreover, in Caco-2:HT29-MTX co-cultures (90:10 and 75:25), levels of occludin mRNA were significantly increased by strain LOC1 compared with untreated co-cultures, and strain LOC1 had higher mRNA levels of MUC2 and MUC4 mucins than L. plantarum ATCC 14917^T and L. plantarum YT9. These results indicate that L. plantarum LOC1 may be used as a safe probiotic with beneficial effects on the intestinal barrier, suggesting that fresh tea leaves could be utilized as a safe source for isolating probiotics.

Bacteriocins, A Natural Weapon Against Bacterial Contamination for Greater Safety and Preservation of Food: A Review

Nowadays, consumers have become increasingly attentive to human health and the use of more natural products. Consequently, the demand for natural preservatives in the food industry is more frequent. This has led to intense research to discover new antimicrobial compounds of natural origin that could effectively fight foodborne pathogens. This research aims to safeguard the health of consumers and, above all, to avoid potentially harmful chemical compounds. Lactobacillus is a bacterial genus belonging to the Lactic Acid Bacteria and many strains are defined GRAS, generally recognized as safe. These strains are able to produce substances with antibacterial activity against food spoilage bacteria and contaminating pathogens: the bacteriocins. The aim of this review was to focus on this genus and its capability to produce antibacterial peptides. The review collected all the information from the last few years about bacteriocins produced by Lactobacillus strains, isolated from clinical or food samples, with remarkable antimicrobial activities useful for being exploited in the food field. In addition, the advantages and disadvantages of their use and the possible ways of improvement for industrial applications were described.

Mining, heterologous expression, purification, antibactericidal mechanism, and application of bacteriocins: A review

Bacteriocins are generally considered as low-molecular-weight ribosomal peptides or proteins synthesized by G⁺ and G^- bacteria that inhibit or kill other related or unrelated microorganisms. However, low yield is an important factor restricting the application of bacteriocins. This paper reviews mining methods, heterologous expression in different systems, the purification technologies applied to bacteriocins, and identification methods, as well as the antibacterial mechanism and applications in three different food systems. Bioinformatics improves the efficiency of bacteriocins mining. Bacteriocins can be heterologously expressed in different expression systems (e.g., Escherichia coli, Lactobacillus, and yeast). Ammonium sulfate precipitation, dialysis membrane, pH-mediated cell adsorption/desorption, solvent extraction, macroporous resin column, and chromatography are always used as purification methods for bacteriocins. The bacteriocins are identified through electrophoresis and mass spectrum. Cell envelope (e.g., cell permeabilization and pore formation) and inhibition of gene expression are common antibacterial mechanisms of bacteriocins. Bacteriocins can be added to protect meat products (e.g., beef and sausages), dairy products (e.g., cheese, milk, and yogurt), and vegetables and fruits (e.g., salad, apple juice, and soybean sprouts). The future research directions are also prospected.

Peptide Extracts from Native Lactic Acid Bacteria Generate Ghost Cells and Spheroplasts upon Interaction with Salmonella enterica, as Promising Food Antimicrobials

Protecting foods from contamination applying peptides produced by lactic acid bacteria is a promising strategy to increase the food quality and safety. Interacting with the pathogen membranes might produce visible changes in shape or cell wall damage. Previously, we showed that the peptides produced by Lactobacillus plantarum UTNGt2, Lactobacillus plantarum UTNCys5-4, and Lactococcus lactis subsp. lactis UTNGt28 exhibit a broad spectrum of antibacterial activity against several foodborne pathogens in vitro. In this study, their possible mode of action against the commensal microorganism Salmonella enterica subsp. enterica ATCC51741 was investigated. The target membrane permeability was determined by detection of beta-galactosidase release from ONPG (o-nitro-phenyl-L-D-galactoside) substrate and changes in the whole protein profile indicating that the peptide extracts destroy the membrane integrity and may induce breaks in membrane proteins to some extent. The release of aromatic molecules such as DNA/RNA was detected after the interaction of Salmonella with the peptide extract. Transmission electronic microscopy (TEM) micrographs depicted at least four simultaneous secondary events after the peptide extract treatment underlying their antimicrobial actions, including morphological alterations of the membrane. Spheroplast and filament formation, vacuolation, and DNA relaxation were identified as the principal events from the Gt2 and Cys5-4 peptide extracts, while Gt28 induced the formation of ghost cells by release of cytoplasmic content, filaments, and separation of cell envelope layers. Gel retarding assays indicate that the Gt2 and Gt28 peptide extracts are clearly binding the Salmonella DNA, while Cys5-4 partially interacted with Salmonella genomic DNA. These results increased our knowledge about the inhibitory mechanism employed by several peptide extracts from native lactic acid bacteria against Salmonella. Further, we shall develop peptide-based formulation and evaluate their biocontrol effect in the food chains.

Efficacy, toxicity study and antioxidant properties of plantaricin E and F recombinants against enteropathogenic Escherichia coli K1.1 (EPEC K1.1)

Enteropathogenic Escherichia coli (EPEC) is one of the resistance bacteria towards antibiotics and have been raising problem during treatments. Therefore, a new antibiotic candidate is required. Plantaricin E and F recombinant have been successfully produced by a GRAS host Lactococcus lactis. This study was aimed to evaluate the efficacy and toxicity of plantaricin E and F recombinant against EPEC K1.1 infection by in vivo assay. The production of plantaricin E and F recombinants from Lactococcus lactis was conducted and encapsulated. The in vivo study was carried out by inoculating the mice perorally with EPEC K1.1 for 7 days then treated with 100, 250, and 500 mg/kg body weight/day of recombinant plantaricin E and F for another 7 days. The toxicity assay were observed in ddY mice using various concentrations of treatment (50, 100, 1000, and 5000 mg/kg/body weight) doses perorally for 48 h. The result showed that the plantaricin E and F recombinant were successfully produced in Lactococcus lactis expression host with 3.7 kDa and 3.8 kDa in size. The efficacy study revealed the optimal doses of plantaricin E and F recombinant against EPEC K1.1 infection was 250 mg/kgBW for plantaricin E and 500 mg/kgBW for plantaricin F. The plantarisin E and F recombinant treatment showed improvement in leukocyte, hematocrit, and hemoglobin levels as well in decreasing malondialdehyde (MDA) level. Observation of the intestine histopathology showed small amounts of mononuclear inflammatory cell infiltration than the other groups of treatment. The acute toxicity assay showed that there was no mortality observed during the assay, even after 5000 mg/kg body weight of plantarisin E and F recombinant treatment (LD₅₀ > 5000 mg/KgBW). The hematological and biochemical observations showed normal levels in leukocytes, erythrocytes, hematocrit, hemoglobin, platelets, urea, creatinine, and alanine transaminase aspartate transaminase (SGOT and SGPT) while histopathological observation shows a picture of normal liver and kidney cells. This study confirmed the application of bacteriocin for further academic and industrial purposes as a non-toxic substance for food preservative and antibiotic candidate.

Characterization of a broad spectrum bacteriocin produced by Lactobacillus plantarum MXG-68 from Inner Mongolia traditional fermented koumiss

An agar well diffusion assay (AWDA) was used to isolate a high bacteriocin-producing strain with a broad spectrum of antibacterial activity, strain MXG-68, from Inner Mongolia traditional fermented koumiss. Lactobacillus plantarum MXG-68 was identified by morphological, biochemical, and physiological characteristics and 16S rDNA analysis. The production of antibacterial substance followed a growth-interrelated model, starting at the late lag phase of 4 h and arriving at a maximum value in the middle of the stationary phase at 24 h. Antibacterial activity was abolished or decreased in the presence of pepsin, chymotrypsin, trypsin, proteinase, and papain K. The results showed that antibacterial substances produced by L. plantarum MXG-68 were proteinaceous and could thus be classified as the bacteriocin, named plantaricin MXG-68. The molar mass of plantaricin MXG-68 was estimated to be 6.5 kDa, and the amino acid sequence of its N-terminal was determined to be VYGPAGIFNT. The mode of plantaricin MXG-68 action was determined to be bactericidal. Bacteriocin in cell-free supernatant (CFS) at pH 7 was stable at different temperatures (60 °C, 80 °C, 100 °C, 121 °C for 30 min; 4 °C and - 20 °C for 30 days), as well as at pH 2.0-10.0. Antibacterial activity maintained stable after treatment with organic solvents, surfactants, and detergents but increased in response to EDTA. Response surface methodology (RSM) revealed the optimum conditions of bacteriocin production in L. plantarum MXG-68, and the bacteriocin production in medium optimized by RSM was 26.10% higher than that in the basal MRS medium.

Regional characteristics of Lactobacillus plantarum group strains isolated from two kinds of Japanese post-fermented teas, Ishizuchi-kurocha and Awa-bancha

Properties of Lactobacillus plantarum group strains isolated from two kinds of Japanese post-fermented teas, Ishizuchi-kurocha and Awa-bancha, were compared. Although lactic acid bacteria isolated from the fermented teas were identified as L. plantarum via homology comparison of 16S ribosomal RNA gene sequences, classification of L. plantarum based on ribosomal proteins showed that the strains isolated from Ishizuchi-kurocha and Awa-bancha were different. According to classification by the ribosomal protein typing, Ishizuchi-kurocha-derived strains belong to the same group as L. plantarum subsp. plantarum JCM 1149^T. Awa-bancha-derived strains were assigned to a different group. This pattern was also applicable to strains isolated more than 10 years ago. A further analysis based on recA and a dnaK gene showed that Awa-bancha-derived strains were closely related to L. pentosus. The interactions with cultured cells were different between strain JCM 1149^T and the Ishizuchi-kurocha-derived strains. The Ishizuchi-kurocha-derived strains showed strong adhesion to Caco-2 cells. In contrast, strain JCM 1149^T and the Awa-bancha-derived strains hardly adhered to Caco-2 cells. According to the ribosomal protein typing, sugar utilization, and interaction with Caco-2 cells, although these properties were dependent on the strain strictly speaking, the L. plantarum group strains in this study can be subdivided into two groups: (1) type strain JCM 1149^T and Ishizuchi-kurocha-derived strains and (2) Awa-bancha-derived strains. A regionally unique microorganism may persist in each traditional fermented drink.

Inhibitory Effect of Substances Produced by Native Lactococcus lactis Strains of Tropical Fruits towards Food Pathogens

The use of peptides produced by lactic acid bacteria (LAB) as antimicrobial agents in food emerged from the increasing need of replacing chemicals with natural substances to ensure their safety and quality. A total of 30 LAB belonging to the genus Lactococcus sp. (10) and Enterococcus sp. (20) were isolated from native fruits of Ecuador subtropical rainforest. Among Lactococcus species, the isolates assigned Gt28, Gt29, and Ella8, identified as Lactococcus lactis subsp. lactis with 99% identity, showing highly inhibitory potential against four food pathogens were further characterized. The treatment of cell-free supernatant with proteolytic enzymes indicated the protein nature of released components, which displayed a broad antimicrobial activity against Gram-positive and -negative bacteria. Polymerase chain reaction analysis indicated the presence of lacticin 3147 gene in all isolates, lactococcin M gene in Gt28 and Gt29 but not in Ella8 and lactococcin A gene in Gt28 only. The antimicrobial activity was not linked to the presence of structural nisin gene as no amplification product was obtained. Treatment of Salmonella enterica ATCC 51741 and Escherichia coli ATCC 25922 at both vegetative and exponential phase of growth with the cell-free supernatant of Gt28 resulted in complete inactivation upon 3 h suggesting its bactericidal mode of action. An increment on inhibitory activity occurred when partial purified bacteriocin Gt28 was combined with ethylenediaminetetraacetic acid rather than bacteriocin only, indicating that the cells were sensitized in vitro by the chelator agent acting synergistically to induce the killing of pathogenic cells.

Construction, heterologous expression, partial purification, and in vitro cytotoxicity of the recombinant plantaricin E produced by Lactococcus lactis against Enteropathogenic Escherichia coli K.1.1 and human cervical carcinoma (HeLa) cells

Lactobacillus plantarum produces bacteriocin called plantaricin that can kill or inhibit other bacteria. Plantaricin E (Pln E), a recombinant bacteriocin, has been successfully constructed and produced by a GRAS host, Lactococcus lactis. A polymerase chain reaction (PCR) overlapping technique has been used to construct a ligation of signal peptide gene, Pln A and bacteriocin encoding gene, Pln E. Furthermore, the fusion fragment were cloned into pNZ8148 vector and transformed into L. lactis NZ3900. Molecular expression study shows that recombinant L. lactis NZ3900 is able to express the mature pln E at transcription level with size of 168 bp. Plantaricin E is purified by ammonium sulphate precipitation followed by gel filtration chromatography. Purified fractions were proven to be active against Enteropathogenic Escherichia coli K.1.1. The other fractions of Pln E also have antibacterial activity against several Gram positive and Gram negative bacteria. Purified recombinant plantaricin E is 3.7 kDa in size. The cytotoxicity assay shows purified Pln E inhibits 46.949 ± 3.338% of HeLa cell lines on 10 ppm dose whilst the metabolite inhibits 53.487 ± 2.957% of HeLa cell line on 100 ppm dose. The IC₅₀ calculation of Pln E metabolite is 107.453 ppm, while the purified protein is 11.613 ppm.

Isolation of antibacterial protein from Lactobacillus spp. and preparation of probiotic curd

The study was aimed to isolate antagonistic lactobacilli and the molecules responsible for their antagonistic ability from curd. Preparation of probiotic curd and the ability of the selected lactobacilli to suppress the pathogen therein was also assessed. All the 116 isolates were identified as Lactobacillus spp. based on morphological, biochemical and curdling assays. Five of these lactobacilli (Lb-17, Lb-33, Lb-108, Lb-112, and Lb-N3) were found most promising to inhibit all test pathogens (Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Salmonella typhi and Shigella sonnei). The cell-free culture supernatants of these five lactobacilli were recorded as thermo-tolerant when subjected to heat treatment at 100 °C for 20 min. The loss in the activity after protease treatment indicated the proteinaceous nature of the antimicrobial molecule present in the culture supernatants. Active protein (19 kDa) produced by lactobacilli was confirmed by SDS-PAGE followed by agar-overlay method. Antibiotic sensitivity assay revealed that the selected Lactobacillus spp. isolates were resistant to methicillin and vancomycin. Probiotic curd prepared by using Lb-108 and Lb-N3 was found to be superior to rest of the three isolates based on organoleptic tests and shelf-life. Complete inhibition of all the test pathogens in curd was shown by Lb-108 and Lb-N3. Inhibition spectrum, production of thermostable protein and preparation of quality curd suggest Lb-108 and Lb-N3 as promising candidates to prepare probiotic curd.

The complete genome sequence of Lactobacillus plantarum LPL-1, a novel antibacterial probiotic producing class IIa bacteriocin

Bacteriocins are antibacterial proteins or peptides synthesized by ribosomes to inhibit or kill both closely related and non-related bacterium. Class IIa bacteriocins possess high activity against foodborne pathogen Listeria monocytogenes. A novel strain Lactobacillus plantarum LPL-1 was isolated from fermented fish and considered as a bacteriocin producing probiotic with great antibacterial activity against Listeria monocytogenes 54002. The complete genome of L. plantarum LPL-1 contains one circular chromosome and plasmid. According to the genome, biosynthetic genes of bacteriocin including precursor, immunity protein,accessory protein and transporter protein were identified; and biosynthetic mechanism of class IIa bacteriocin was also further analyzed. The antibacterial activity of purified bacteriocin against L.monocytogenes54002 was determined and the diameter of inhibition zone was about 16.6 mm by vernier caliper. This work provided the complete genome information of L. plantarum LPL-1 that could benefit for understanding the biosynthetic mechanism of class IIa bacteriocin as well as the potential application of L. plantarum LPL-1 in nutraceutical and pharmaceutical.

Functional Analysis of Plantaricin E and Its Mutant by Heterologous Expression in Escherichia coli

Plantaricins are a group of ribosomally synthesized antimicrobial peptides in Lactobacillus plantarum that exert antimicrobial activities against some foodborne pathogens. In this study, we observed that plantaricin E in L. plantarum 163 was missing 19 amino acids (plnE mutant amino acid sequence: FNRGGYNFGKSVRH, plnE amino acid sequence: FNRGGYNFGKSVRHVVDAIGSVAGIRGILKSIR). In order to study the effects of mutant plnE, plnE mutant genes with and without the signal peptide were cloned from the L. plantarum 163 genome, linked to the pET32a vector, and expressed via a fusion protein (thioredoxin) in Escherichia coli BL21 (DE3). All target proteins were purified using Ni-NTA, SP FF columns, and RP-HPLC. The purified proteins were stable in an acidic environment and at temperatures below 80 °C, but they were easily degraded under alkaline conditions and by protease treatment. They showed antimicrobial activity against gram-positive bacteria such as Micrococcus luteus, Staphylococcus epidermidis, Lactococcus lactis, Lactobacillus paracasei, and Listeria innocua. In addition, SP-plnE and PlnE exerted stronger activity than nisin. The signal peptide had a positive effect on the activities of PlnE and PlnEm. Thus, these purified proteins may have potential applications in the food industry to control foodborne pathogens.

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.