Purification and characterization of bacteriocin produced by a strain of Lacticaseibacillus rhamnosus ZFM216

Bio-induced overproduction of heterocycloanthracin-like bacteriocin in Lysinibacillus macroides by Aspergillus austroafricanus: optimization of medium conditions and evaluation of potential applications

BACKGROUND

Plants and microorganisms are at the forefront of natural exploitable bioresources for the discovery of novel bioactive compounds (BACs) to provide solutions to food and agricultural challenges. The present study aimed to produce a novel biotechnologically-relevant BAC from a mangrove sediment bacterium under optimized bioprocess medium conditions. The BAC-producing bacteria were isolated via the crowded plate technique, and medium optimization was performed via sequential statistics of response surface methodology (RSM). The RSM model predictions were optimized, validated, and scaled up in a 5-L bioreactor via submerged batch fermentation. The BAC was extracted with ethyl acetate, purified via silica gel column chromatography, and identified via semipreparative high-performance liquid chromatography using bioactive standards with known retention times. The biocontrol, antioxidant and biopreservation potential of the BAC were evaluated via standard methods.

RESULTS

The results revealed that strain GKRMS-A9 produced the largest inhibition zone diameter (ZND) of 17 mm against the susceptible mould. The bacterium and its susceptible mould were identified as Lysinibacillus macroides and Aspergillus austroafricanus strains, respectively. Bioprocess medium optimization produced 9.6 g L- 1 of the BAC with a ZND of 47.1 mm using 44.84% [v v- 1] rice processing effluent, 8.58 gL- 1 casamino acid, 1.39 g L- 1 MgSO4.7H2O, 2.78 g L- 1 CaCl2.2H2O, 16.94% [v v- 1] inoculum volume, and 10.45 g L- 1 Na2HPO4/NaH2PO4. The BAC concentration increased 48.7-fold in response to biological induction with susceptible mould. Silica gel chromatography revealed 9 bioactive fractions in the ethyl acetate extract, with fraction C (retention time of 9.02 min) eliciting the largest mean ZND of 38.1 ± 1.7 mm against Aspergillus austroafricanus. Fraction C was identified as a heterocycloanthracin-like class II bacteriocin with a molecular weight of 10.5 kDa.

CONCLUSION

The bacteriocin 'macroidin' is stable over a wide range of pH values and temperatures and has significant antimicrobial activity against Gram-positive food-borne and phytopathogenic strains of bacteria and moulds. Its antioxidant activities against DPPH and ABTS*+ radicals are comparable to those of ascorbic acid, making this biomolecule a promising agent for biopreservation and phytopathogen control applications in the food and agricultural sectors.

Preliminary Purification and Partial Characterization of a Functional Bacteriocin of Lacticaseibacillus paracasei Zhang and Mining for its Gene Cluster

Bacteriocins produced by lactic acid bacteria (LAB) have good potential for use as food biopreservatives. Lacticaseibacillus paracasei Zhang (L. paracasei Zhang) is both a food use and a probiotic bacterium. This study aimed to purify and preliminary characterize the active antibacterial metabolite of L. paracasei Zhang. The cell-free supernatant of L. paracasei Zhang was collected and purified by ultrafiltration and gel filtration chromatography. The 1-3 kDa active fraction could inhibit the growth of Staphylococcus aureus but not Escherichia coli. Further antibacterial activity assays revealed its capacity to suppress various foodborne and human opportunistic pathogens (including Staphylococcus aureus, Pseudomonas fluorescens, Pseudomonas aeruginosa, Listeria monocytogenes, and Bacillus cereus), but not fungi. The antibacterial activity showed good tolerance to heat (40 to 100 °C), acid-base (pH 2-3 and pH 6-10), and digestions by a number of industrial and animal/human enzymes (such as trypsin, pepsin, α-amylase, and protease K, except papain); these desired properties make it a suitable biopreservative to be used in harsh and complex industrial production processes. The high papain sensitivity suggested a proteinaceous/peptide nature of the bioactivity. Moreover, our genomic data mining for bacteriocin through BAGEL4 revealed an area of interest encoding a complete set of putative genes required for bacteriocin production. In conclusion, our study showed that L. paracasei Zhang can produce extracellular functional antibacterial metabolite, likely a class II bacteriocin. Our preliminary extraction and characterization of the active metabolite demonstrated that it has good potential to be used as a biopreservative or an agent for suppressing gastrointestinal infections.

Bacteriocin Mining in Lactiplantibacillus pentosus PCZ4 with Broad-Spectrum Antibacterial Activity and Its Biopreservative Effects on Snakehead Fish

Some lactic acid bacteria (LAB) produce antibacterial substances such as bacteriocins, making them promising candidates for food preservation. In our study, Lactiplantibacillus pentosus PCZ4-a strain with broad-spectrum antibacterial activity-was isolated from traditional fermented kimchi in Sichuan. Whole-genome sequencing of PCZ4 revealed one chromosome and three plasmids. Through BAGEL4 mining, classes IIa and IIb bacteriocin plantaricin S were identified. Additionally, two new antibacterial peptides, Bac1109 and Bac2485, were predicted from scratch by limiting open reading frames. Furthermore, during refrigerated storage of snakehead fish, PCZ4 crude extract reduced the total bacterial count, slowed the increase in TVB-N and pH values, improved the sensory quality of the snakehead, and extended its shelf life by 2 days. Meanwhile, PCZ4 effectively inhibited the growth of artificially contaminated Aeromonas hydrophila in snakehead fish. These findings indicate that Lp. pentosus PCZ4 can produce multiple antibacterial substances with strong potential for food preservation applications.

Activity and safety evaluation of natural preservatives

Synthetic preservatives are widely used in the food industry to control spoilage and growth of pathogenic microorganisms, inhibit lipid oxidation processes and extend the shelf life of food. However, synthetic preservatives have some side effects that can lead to poisoning, cancer and other degenerative diseases. With the improvement of living standards, people are developing safer natural preservatives to replace synthetic preservatives, including plant derived preservatives (polyphenols, essential oils, flavonoids), animal derived preservatives (lysozyme, antimicrobial peptide, chitosan) and microorganism derived preservatives (nisin, natamycin, ε-polylysine, phage). These natural preservatives exert antibacterial effects by disrupting microbial cell wall/membrane structures, interfering with DNA/RNA replication and transcription, and affecting protein synthesis and metabolism. This review summarizes the natural bioactive compounds (polyphenols, flavonoids and terpenoids, etc.) in these preservatives, their antioxidant and antibacterial activities, and safety evaluation in various products.

Acetolactate Decarboxylase as an Important Regulator of Intracellular Acidification, Morphological Features, and Antagonism Properties in the Probiotic Lactobacillus reuteri

SCORE

This study identifies the coding gene (aldB) of acetolactate decarboxylase (ALDC) as an important regulatory gene of the intracellular pH in Lactobacillus reuteri (L. reuteri), uncovering the important role of ALDC in regulating intracellular pH, morphological features, and antagonism properties in the probiotic organism L. reuteri.

METHODS AND RESULTS

The aldB mutant (ΔaldB) of L. reuteri is established using the homologous recombination method. Compare to the wild-type (WT) strain, the ΔaldB strain shows a smaller body size, grows more slowly, and contains more acid in the cell cytoplasm. The survival rate of the ΔaldB strain is much lower in low pH and simulated gastric fluid (SGF) than that of the WT strain, but higher in simulated intestinal fluid (SIF). The antagonism test demonstrates the ΔaldB strain can inhibit Listeria monocytogenes (L. monocytogenes) and Salmonella more effectively than the WT strain. Additionally, there is a dramatic decrease in the adhesion rate of Salmonella to Caco-2 and HT-29 cells in the presence of the ΔaldB strain compared to the WT strain. Simultaneously analyze, the auto-aggregation, co-aggregation, cell surface hydrophobicity (CSH), hemolytic, temperature, NaCl, oxidative stress, and antibiotic susceptibility of the ΔaldB strain are consistent with the features of probiotics.

CONCLUSION

This study highlights that the aldB gene plays a significant role in the growth and antibacterial properties of L. reuteri.