Production and purification of a bacteriocin peptide produced by Lactococcus sp. strain GM005, isolated from Miso-paste

Soybean fermentation: Microbial ecology and starter culture technology

Fermented soybean products, including Soya sauce, Tempeh, Miso, and Natto have been consumed for decades, mainly in Asian countries. Beans are processed using either solid-state fermentation, submerged fermentation, or a sequential of both methods. Traditional ways are still used to conduct the fermentation processes, which, depending on the fermented products, might take a few days or even years to complete. Diverse microorganisms were detected during fermentation in various processes with Bacillus species or filamentous fungi being the two main dominant functional groups. Microbial activities were essential to increase the bean's digestibility, nutritional value, and sensory quality, as well as lower its antinutritive factors. The scientific understanding of fermentation microbial communities, their enzymes, and their metabolic activities, however, still requires further development. The use of a starter culture is crucial, to control the fermentation process and ensure product consistency. A broad understanding of the spontaneous fermentation ecology, biochemistry, and the current starter culture technology is essential to facilitate further improvement and meet the needs of the current extending and sustainable economy. This review covers what is currently known about these aspects and reveals the limited available information, along with the possible directions for future starter culture design in soybean fermentation.

Bacteriocin activity of various iranian honey-associated bacteria and development of a simple medium for enhanced bacteriocin activity

PURPOSE

Honey is a promising source of bacterial strains producing metabolites with antimicrobial activity. There is a great variety in the antimicrobial activity of honey from different areas of nature. Therefore, the aim of present study was to investigate the antibacterial activity of Iranian honey from different regions and to optimize the culture condition for the highly potent bacterial isolate.

METHODS

Honey samples were collected from ten different regions of Iran and were screened for bacteriocin-producing bacteria. The best bacteriocin-producing strain was characterized and identified by 16S rDNA analysis. One-factor-at-a-time method was used for optimization of culture medium and the yield and time-course of bacteriocin production were compared in both shake flask and bio-reactor.

RESULTS

The Bacillus subtilis SB1 that was isolated from Sabalan honey showed potent antibacterial activity with prominent thermal stability. The optimum medium for the bacteiocin production was a yeast extract-based medium. The optimum incubation temperature for bacteriocin production was 34 °C. Bacteriocin production was higher near neutral pH conditions than that produced at acidic or alkaline environment. The results of cell growth and bacteriocin assays revealed that the exponential phase of growth and antibacterial compounds production was started rapidly in bioreactor than flask.

CONCLUSIONS

Findings of this study supported the folkloric application of honey against some infectious diseases. B.subtilis SB1 that isolated from Sabalan honey was a potential source for bacteriocins-like compounds. Our studies suggested a simple buffered nitrogen-based medium for SB1 growth and bacteriocin activity in both shake flask and bioreactor.

Fermented Foods: Definitions and Characteristics, Impact on the Gut Microbiota and Effects on Gastrointestinal Health and Disease

Fermented foods are defined as foods or beverages produced through controlled microbial growth, and the conversion of food components through enzymatic action. In recent years, fermented foods have undergone a surge in popularity, mainly due to their proposed health benefits. The aim of this review is to define and characterise common fermented foods (kefir, kombucha, sauerkraut, tempeh, natto, miso, kimchi, sourdough bread), their mechanisms of action (including impact on the microbiota), and the evidence for effects on gastrointestinal health and disease in humans. Putative mechanisms for the impact of fermented foods on health include the potential probiotic effect of their constituent microorganisms, the fermentation-derived production of bioactive peptides, biogenic amines, and conversion of phenolic compounds to biologically active compounds, as well as the reduction of anti-nutrients. Fermented foods that have been tested in at least one randomised controlled trial (RCT) for their gastrointestinal effects were kefir, sauerkraut, natto, and sourdough bread. Despite extensive in vitro studies, there are no RCTs investigating the impact of kombucha, miso, kimchi or tempeh in gastrointestinal health. The most widely investigated fermented food is kefir, with evidence from at least one RCT suggesting beneficial effects in both lactose malabsorption and Helicobacter pylori eradication. In summary, there is very limited clinical evidence for the effectiveness of most fermented foods in gastrointestinal health and disease. Given the convincing in vitro findings, clinical high-quality trials investigating the health benefits of fermented foods are warranted.

Metabolites of stable fly reduce diarrhea in mice by modulating the immune system, antioxidants, and composition of gut microbiota

Escherichia coli (E. coli) O₁-induced diarrhea is associated with intestinal microbial imbalance, however, the results of using oral antibiotics still remain poor. To overcome such problem, our study investigates the role of metabolites from stable flies (MSF) in the occurrence of diarrhea. The amino acid composition and molecular weight analysis of MSF by RP-HPLC and GPC, respectively. Besides the normal control group, SPF mice in other group were inoculated with E. coli O1 received treatment as follows over a period of 7 days saline solution (E. coli control), ciprofloxacin (0.13 g/kg; positive control) and MSF (2, 4 and 8 mg/kg) dosage. Throughout the experiment, defecation and body weights were examined and recorded. On the eighth day, after administering anesthesia, blood, tissue of small intestine samples were obtained for immunological and anti-oxidant. Small intestinal tissues and cecum contents samples were used for histopathological and 16S rDNA sequencing analysis. Our showed that MSF was rich in isoleucine, and its molecular weight less than 400 Da is 60.03%. MSF (4 and 8 mg/kg) and ciprofloxacin, significantly decreased IL-6, IL-8 and TNF-α levels, whereas, increased IL-2, IL-4, IL-10, INF-γ, IgA and IgG levels in mice having diarrhea. These treatments also reversed intestinal flora imbalance as indicated by the increased in Firmicutes-to-Bacteroidetes ratio and Clostridium levels (P < 0.05) and improved 5-HT, CAT and SOD levels. MSF favored diarrhea management as compared to ciprofloxacin, suggesting that MSF can be used in the management of E. coli O₁-induced diarrhea, in normal gut microbiota and normal intestinal antioxidant function.

Mode of action of a novel anti-Listeria bacteriocin (CAMT2) produced by Bacillus amyloliquefaciens ZJHD3-06 from Epinephelus areolatus

Bacteriocin CAMT2, produced by Bacillus amyloliquefaciens ZJHD3-06, has been shown to exhibit protective activity against important food spoilage and food-borne bacterial pathogens. This study was conducted to investigate the mode of action of bacteriocin CAMT2 against highly pathogenic Listeria monocytogenes ATCC 19111. The addition of bacteriocin CAMT2 at 64 AU/ml inhibited L. monocytogenes ATCC 19111. An efflux of K⁺ ions, lactic acid dehydrogenase and an increase in extracellular electrical conductivity was observed in CAMT2-treated L. monocytogenes. Electron microscopy showed morphological alterations such as uneven cell surface, accumulation of cell debris and bacterial lysis. These results show that bacteriocin CAMT2 inhibit L. monocytogenes by increasing cell permeability and inducing membrane damage, hence it has the great application potentials in ensuring food safety.

Antilisterial Bacteriocin-producing Strain of Lactobacillus curvatus CWBI-B28 as a Preservative Culture in Bacon Meat and Influence of Fat and Nitrites on Bacteriocins Production and Activity

The objectives of this study were to evaluate the effectiveness of a bacteriocin-producing Lactobacillus curvatus CWBI-B28 to inhibit the growth of Listeria monocytogenes in de Man, Rogosa and Sharp (MRS) broth and in bacon meat. A co-culture of L. monocytogenes with the Bac strain in MRS broth, resulted in a reduction of the pathogen counts by 4.2 log cycles after 24h of incubation at 37°C. In bacon, the counts of L. monocytogenes was reduced to below the detectable limit (<10cfu/g) in samples inoculated with the Bac strain within 1 or 2 weeks in absence or presence of nitrites (210mg/kg), respectively. However, a week later, a re-growth of the pathogen has occurred. In contrast, no such reduction in Listeria cfus was observed in samples treated with the Bac derivative of Lb. curvatusCWBI-B28. Nonetheless, the extent of inhibitory effect of the Bac strain against L. monocytogenes in bacon was somewhat reduced in the presence of nitrites. A separate study on the influence of nitrites and fats on growth and bacteriocin production by Lb. curvatus CWBI-B28 revealed that the curing agent affects the growth of the Bac strain and, thereby bacteriocin production and activity only at concentrations (>5%) far beyond those allowed in the meat industry. Fat content did not affect the bacterial growth even at the highest concentration used (i.e. 50%), however, it interfered significantly with the detection of AUs and the antilisterial activity. Use of the Bac Lb. curvatus CWBI-B28 has proven efficient in controlling L. monocytogenes in bacon despite the slight antagonistic effect of nitrites, however the efficacy was dramatically reduced upon extended period of storage at 4°C.

Human microbiome versus food-borne pathogens: friend or foe

As food safety advances, there is a great need to maintain, distribute, and provide high-quality food to a much broader consumer base. There is also an ever-growing "arms race" between pathogens and humans as food manufacturers. The human microbiome is a collective organ of microbes that have found community niches while associating with their host and other microorganisms. Humans play an important role in modifying the environment of these organisms through their life choices, especially through individual diet. The composition of an individual's diet influences the digestive system-an ecosystem with the greatest number and largest diversity of organisms currently known. Organisms living on and within food have the potential to be either friends or foes to the consumer. Maintenance of this system can have multiple benefits, but lack of maintenance can lead to a host of chronic and preventable diseases. Overall, this dynamic system is influenced by intense competition from food-borne pathogens, lifestyle, overall diet, and presiding host-associated microbiota.

An evaluation and partial characterization of a bacteriocin produced by Lactococcus lactis subsp lactis ST1 isolated from goat milk

A bacteriocin-like inhibitory substance producing Lactococcus lactis subsp lactis strain, ST1, isolated from goat milk of Iranian origin and with broad spectrum of activity and desirable technical properties was used for evaluating some futures of bacteriocin inhibitory activity. Cell growth and bacteriocin production studies were carried out in MRS medium incubated statically under uncontrolled pH condition. The antibacterial activity presented a primary metabolite pattern and showed a rapid decrease at the stationary phase. Microaerobiosis and capnophily growth conditions resulted in higher bacteriocin production while aerobiosis showed negative effect on both cell growth and bacteriocin production. Bacteriocin production, on the other hand, was favored in MRS broth (pH; 6.5) inoculated with 0.1 ml l^-1 fresh culture when incubation was carried out at 30 °C. This indicated that the conditions resulted in higher levels of growth were frequently favoring bacteriocin production by ST1 as well. Decrease in activity, at the stationary growth phase, was much pronounced in favored growth condition. Nutrient depletion, deferent effect of low pH on bacteriocin production and/or protein degradation seemed more responsible for this phenomenon. The study also provided further data on new method for bacteriocin release from the cell wall of producer. It was clearly shown that both heating and ultrasound shock for 5 min at pH 2 could increase bacteriocin activity significantly. The release was more pronounced in the presence of 0.5% Tween80.

Inhibitory activity against the fish pathogen Lactococcus garvieae produced by Lactococcus lactis TW34, a lactic acid bacterium isolated from the intestinal tract of a Patagonian fish

After enrichment of Odontesthes platensis intestinal contents, 53 lactic acid bacteria (LAB) were isolated. From the four isolates that showed inhibitory activity against Lactococcus garvieae 03/8460, strain TW34 was selected because it exerted the strongest inhibition. It also inhibited other Gram-positive bacteria, but not Gram-negative fish pathogens. Phenotypic and 16S rDNA phylogenetic analyses showed that TW34 belongs to Lactococcus lactis. In addition, TW34 showed to be sensitive to different antibiotics. The production of the inhibitory agent against L. garvieae was growth associated, and it was significantly influenced by the incubation temperature. The optimal temperature for the antimicrobial production was as low as 15 degrees C. Both acidification and hydrogen peroxide production were ruled out as the source of inhibition. In contrast, the antimicrobial activity was completely lost by treatment with proteolytic enzymes, which confirmed that the inhibitory substance was a bacteriocin. The bacteriocin was highly thermostable (121 degrees C for 15 min) and active between pH 3 and 11. It remained stable for up to 2 months when stored at 4 degrees C and up to 6 months at -20 degrees C. Our results suggest that the strain L. lactis TW34 could provide an alternative for lactococcosis control and therefore be considered for future challenge experiments with fish.

Further characterization of a bacteriocin produced by Lactobacillus paracasei HL32

AIMS

Purification, identification and partial characterization of bacteriocin produced by Lactobacillus paracasei HL32. It has been shown to have activity against Porphyromonas sp.

METHODS AND RESULTS

The purification of bacteriocin consisting of gel exclusion followed by anion exchange chromatography produced a single band upon an electrophoresis gel with a molecular weight corresponding to 56 kDa. The isolated protein contained 171 amino acids and the first 151 were sequenced. The bacteriocin contained a high percentage of cationic amino acids near the N-terminus, hydrophobic amino acids in the central region (Leu, Ile, Val, Phe, Trp and Gly) and hydrophilic residues (Ser, Asn and Gln) at the C-terminus. This structure did not match with that of previously reported bacteriocins. The antimicrobial activity of the bacteriocin was determined against some pathogens and normal microbiota (P. gingivalis, P. intermedia, T. forsythensis, S. salivarius and S. sanguinis) found in saliva and crevicular fluid. The bacteriocin was found to inhibit P. gingivalis at the minimum bactericidal concentration (MBC) of 0.14 mmol l(-1), but was found not to inhibit the other oral micro-organisms. The bacteriocin was found from transmission electron microscopy studies to cause pore formation in the cytoplasmic membranes of P. gingivalis at the pole and induce potassium efflux. Bacteriocin concentrations of two to four times of MBC were shown to induce haemolysis. The bacteriocin was heat-stable, surviving at 110 degrees C under pressure and possessed activity over a pH range of 6.8-8.5. Only a small reduction of activity was found to occur after incubation in biological fluids (saliva and crevicular fluid).

CONCLUSIONS

A novel bacteriocin has been identified that has selective activity against Porphyromonas sp. associated with periodontal disease.

SIGNIFICANCE AND IMPACT OF THE STUDY

The findings of this work gained the knowledge of specific antibacterial activity of bacteriocin against Porphyromonas gingivalis.

Effects of prebiotic oligosaccharides and trehalose on growth and production of bacteriocins by lactic acid bacteria

AIMS

To investigate the effects of two prebiotics and trehalose on the production of bacteriocins.

METHODS AND RESULTS

Four carbohydrates [dextrose, fructo-oligosaccharides (FOS), raffinose, and trehalose] were used as the sole carbon source in a simple broth. Five bacteriocin-producing strains of bacteria, including those producing nisin, enteriocin, and other bacteriocins, were used, and their inhibitory activities when grown on each carbohydrate were determined. The inhibitory activity assay was performed using the agar well diffusion method, and Lactobacillus sakei JCM 1,157(T) was used as the indicator strain. Effective enhancement of bacteriocin production was observed with FOS and trehalose incubation.

CONCLUSIONS

The results suggest that FOS and trehalose can effectively enhance the production of the five kinds of bacteriocins evaluated in this study.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study offers useful information for not only a new application of FOS and trehalose, but also the potential improvement of food preservation.

Antibacterial activity of a bacteriocin from Lactobacillus paracasei HL32 against Porphyromonas gingivalis

Porphyromonas gingivalis infections cause problems in periodontal diseases and in certain systemic diseases. There is evidence that Lactobacillus spp. can control populations of P. gingivalis, but there are few data on the effects of purified bacteriocins from Lactobacillus paracasei HL32 on P. gingivalis. The objective of this study was to examine the antibacterial activity of a bacteriocin from L. paracasei HL32 and to relate this activity to its composition. A bacteriocin was purified from culture supernatants of Lactobacillus spp. using a dialysis technique followed by gel-permeation chromatography. Composition of the bacteriocin was characterised by ninhydrin tests, ultraviolet spectrophotometry, thin-layer chromatography, sodium-dodecyl sulphate-polyacrylamide gel electrophoresis, electrospray ionisation mass spectrometry and amino acid analysis. The amino acid sequence from the N-terminal of the bacteriocin was determined. Antibacterial activity was examined by the cylinder plate method, microtitre assay and scanning electron microscopy as compared with standard antibiotics. The bacteriocin had a molecular weight of approximately 56kDa, was comprised of 68% carbohydrate and 32% protein, and showed maximum peak absorbance at 214 and 254nm. The bacteriocin was found to be effective against P. gingivalis; it caused swelling and pore formation on the cell envelope at a minimum bactericidal concentration of 0.14mM, and caused death within 2h. Metronidazole killed P. gingivalis but did not affect the envelope, whereas tetracycline affected P. gingivalis with cell deformation. In conclusion, the bacteriocin from L. paracasei HL32 had the ability to kill P. gingivalis, suggesting that it could be a promising alternative chemotherapeutic agent for P. gingivalis infections.

Isolation and characterization of lactic acid bacteria from dochi (fermented black beans), a traditional fermented food in Taiwan

AIMS

To isolate, characterize and identify lactic acid bacteria (LAB) in dochi (fermented black beans), a traditional fermented food in Taiwan.

METHODS AND RESULTS

A total of 30 samples were collected from three different dochi producers and analysed after different periods of storage. Fifty-two cultures of LAB were isolated from dochi samples and the isolates were divided into classes by phenotype and then into groups by restriction fragment length polymorphism analysis and sequencing of 16S ribosomal DNA. Phenotypic and biochemical characteristics identified six different bacterial groups (A-F) and showed that the majority of the isolates were homofermentative LAB. Enterococcus faecium was the most abundant of the dochi-isolated LAB. All isolated LAB were able to grow in MRS broth containing 6% NaCl, but only Enterococcus, Pediococcus and Tetragenococcus species could grow in MRS broth containing 10% NaCl. Furthermore, antibacterial activities of isolates were determined, and four isolates showed inhibitory activities against the indicator strain Lactobacillus sakei JCM 1157(T).

CONCLUSIONS

These results suggest that Ent. faecium is the main LAB present during the fermentation of dochi.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report describing the distribution and varieties of LAB that exist in the dochi fermentation process.

Isolation and characterization of lactic acid bacteria from suan-tsai (fermented mustard), a traditional fermented food in Taiwan

AIMS

To isolate, characterize, and identify lactic acid bacteria (LAB) in suan-tsai (fermented mustard), a traditional fermented food in Taiwan.

METHODS AND RESULTS

Suan-tsai samples were collected at five time points from a fixed fermenting bucket. Fifty cultures were isolated from suan-tsai samples, and isolates were divided into classes by phenotype and then into groups by restriction-fragment length polymorphism analysis and sequencing of 16S ribosomal DNA. Phenotypic and biochemical characteristics identified two different bacterial groups (A and B), and the results showed that Pediococcus pentosaceus was the most abundant LAB during the initial fermentation time. However, the more NaCl-tolerant species Tetragenococcus halophilus took the place of P. pentosaceus and became the most abundant LAB later. All isolates were grown in de Man, Rogosa, and Sharpe (MRS) broth containing 6% NaCl, but T. halophilus could grow only in MRS broth containing 10% NaCl.

CONCLUSIONS

These results suggest that the LAB P. pentosaceus and T. halophilus play roles in the fermentation of suan-tsai.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report describing the distribution and varieties of LAB that exist in the suan-tsai fermentation process.

Searching for bacteriocin-producing lactic acid bacteria in soil

A survey was conducted on the isolation and characterization of bacteriocin-producing lactic acid bacteria in soil. Forty-two acid-producing bacterial strains were isolated from 55 soil samples collected in Yamanashi prefecture, Japan. Investigation of antibacterial activities of isolates revealed that three isolates, Lactobacillus animalis C060203, Enterococcus durans C102901 and Leuconostoc mesenteroides subsp. mesenteroides C060204, showed antibacterial activities against the indicator strain of Lactobacillus sakei JCM 1157T. Bacteriocin from Enterococcus durans C102901 showed different characteristics from the known durancin L28-1A, produced by Enterococcus durans L28-1. Furthermore, this is the first report of a bacteriocin being produced by Lactobacillus animalis. Viewing from the species, bacteriocins from strains C102901 and C060203 showed high possibilities for the novel substances. These significant findings suggest that soil may be a common source for the isolation of novel bacteriocin-producing lactic acid bacteria.

Durancin L28-1A, a new bacteriocin from Enterococcus durans L28-1, isolated from soil

AIMS

To isolate, characterize and identify bacteriocins from lactic acid bacteria in soil.

METHODS AND RESULTS

Thirty-four acid-producing bacteria were isolated from 87 soil samples. Antibacterial activities were detected, and one strain, L28-1 produced a bacteriocin that was active against some Gram-positive bacteria. L28-1 was identified as Enterococcus durans by 16S rDNA sequence analysis and API50CHL. This bacteriocin did not lose its activity after autoclaving (121 degrees C for 15 min), but was inactivated by protease K. The bacteriocin was purified by hydrophobic column chromatography, and Sep-Pak C(18). Tricine sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the partially purified bacteriocin contained numerous protein bands. Two bands that displayed antibacterial activities were c. 3.4 and 2.5 kDa in size. In this work, the 3.4-kDa bacteriocin was analysed with N-terminal amino acid and DNA sequencing and matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis. The results indicated that the 3.4-kDa bacteriocin of Ent. durans L28-1 is a new natural enterocin variant.

CONCLUSIONS

Enterococcus durans L28-1 produced a new bacteriocin.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study reports a novel bacteriocin that is produced by Ent. durans that has potential for use as a food preservative.

Purification and characterisation of acidocin D20079, a bacteriocin produced by Lactobacillus acidophilus DSM 20079

Bacteriocins are natural antimicrobial agents produced by food fermentative bacteria. Lactobacillus acidophilus DSM 20079 produces a small bacteriocin, with a molecular mass of 6.6 kDa, designated acidocin D20079. This antimicrobial peptide was extremely heat-stable (30 min at 121 degrees C) and was active over a wide pH range. It was found to be sensitive to proteolytic enzymes (trypsin, ficin, pepsin, papain, and proteinase K). Acidocin D20079 has a narrow inhibitory spectrum restricted to the genus Lactobacillus which includes L. sakei NCDO 2714, an organism known to cause anaerobic spoilage of vacuum-packaged meat. Maximum production of acidocin D20079 in MRS broth was detected at pH 6.0, and the peptide was purified by ammonium sulphate precipitation followed by sequential cation exchange and hydrophobic interaction chromatography. Purified acidocin D20079 spontaneously formed spherulite crystals during dialysis. As the N-terminus was found to be blocked for sequencing, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was used to determine a partial sequence, and the molecular mass of the bacteriocin in the formed crystals (6.6 kDa). Estimates of the molecular weight of the partially purified peptide, using tricine-SDS-PAGE, in which bacteriocin activity was confirmed by overlayer techniques were in accordance with this value.