Characterization of brevilaterins, multiple antimicrobial peptides simultaneously produced by Brevibacillus laterosporus S62-9, and their application in real food system

Food-derived peptides unleashed: emerging roles as food additives beyond bioactivities

Innovating food additives stands as a cornerstone for the sustainable evolution of future food systems. Peptides derived from food proteins exhibit a rich array of physicochemical and biological attributes crucial for preserving the appearance, flavor, texture, and nutritional integrity of foods. Leveraging these peptides as raw materials holds great promise for the development of novel food additives. While numerous studies underscore the potential of peptides as food additives, existing reviews predominantly focus on their biotic applications, leaving a notable gap in the discourse around their abiotic functionalities, such as their physicochemical properties. Addressing this gap, this review offers a comprehensive survey of peptide-derived food additives in food systems, accentuating the application of peptides' abiotic properties. It furnishes a thorough exploration of the underlying mechanisms and diverse applications of peptide-derived food additives, while also delineating the challenges encountered and prospects for future applications. This well-time review will set the stage for a deeper understanding of peptide-derived food additives.

Dietary Supplementation of Brevibacillus laterosporus S62-9 Improves Broiler Growth and Immunity by Regulating Cecal Microbiota and Metabolites

Brevibacillus laterosporus has been added as a direct-fed microbiota to chicken. Yet, few studies have reported the effects of B. laterosporus on broiler growth and gut microbiota. The aim of this study was to evaluate the effects of B. laterosporus S62-9 on growth performance, immunity, cecal microbiota, and metabolites in broilers. A total of 160 1-day-old broilers were randomly divided into S62-9 and control groups, with or without 106 CFU/g B. laterosporus S62-9 supplementation, respectively. During the 42 days feeding, body weight and feed intake were recorded weekly. Serum was collected for immunoglobulin determination, and cecal contents were taken for 16S rDNA analysis and metabolome at Day 42. Results indicated that the broilers in S62-9 group showed an increase in body weight of 7.2% and 5.19% improvement in feed conversion ratio compared to the control group. The B. laterosporus S62-9 supplementation promoted the maturation of immune organs and increased the concentration of serum immunoglobulins. Furthermore, the α-diversity of cecal microbiota was improved in the S62-9 group. B. laterosporus S62-9 supplementation increased the relative abundance of beneficial bacteria including Akkermansia, Bifidobacterium, and Lactobacillus, while decreased the relative abundance of pathogens including Klebsiella and Pseudomonas. Untargeted metabolomics revealed that 53 differential metabolites between the two groups. The differential metabolites were enriched in 4 amino acid metabolic pathways, including arginine biosynthesis and glutathione metabolism. In summary, B. laterosporus S62-9 supplementation could improve the growth performance and immunity through the regulation of gut microbiota and metabolome in broilers.

New strain Brevibacillus laterosporus TSA31-5 produces both brevicidine and brevibacillin, exhibiting distinct antibacterial modes of action against Gram-negative and Gram-positive bacteria

The growing prevalence of antibiotic resistance has made it imperative to search for new antimicrobial compounds derived from natural products. In the present study, Brevibacillus laterosporus TSA31-5, isolated from red clay soil, was chosen as the subject for conducting additional antibacterial investigations. The fractions exhibiting the highest antibacterial activity (30% acetonitrile eluent from solid phase extraction) were purified through RP-HPLC. Notably, two compounds (A and B) displayed the most potent antibacterial activity against both Escherichia coli and Staphylococcus aureus. ESI-MS/MS spectroscopy and NMR analysis confirmed that compound A corresponds to brevicidine and compound B to brevibacillin. Particularly, brevicidine displayed notable antibacterial activity against Gram-negative bacteria, with a minimum inhibitory concentration (MIC) range of 1-8 μg/mL. On the other hand, brevibacillin exhibited robust antimicrobial effectiveness against both Gram-positive bacterial strains (MIC range of 2-4 μg/mL) and Gram-negative bacteria (MIC range of 4-64 μg/mL). Scanning electron microscopy analysis and fluorescence assays uncovered distinctive morphological alterations in bacterial cell membranes induced by brevicidine and brevibacillin. These observations imply distinct mechanisms of antibacterial activity exhibited by the peptides. Brevicidine exhibited no hemolysis or cytotoxicity up to 512 μg/mL, comparable to the negative control. This suggests its promising therapeutic potential in treating infectious diseases. Conversely, brevibacillin demonstrated elevated cytotoxicity in in vitro assays. Nonetheless, owing to its noteworthy antimicrobial activity against pathogenic bacteria, brevibacillin could still be explored as a promising antimicrobial agent.

Action mechanism of the potential biocontrol agent Brevibacillus laterosporus SN19-1 against Xanthomonas oryzae pv. oryzae causing rice bacterial leaf blight

The causal agent of rice bacterial leaf blight (BLB) is Xanthomonas oryzae pv. oryzae (Xoo), which causes serious damage to rice, leading to yield reduction or even crop failure. Brevibacillus laterosporus SN19-1 is a biocontrol strain obtained by long-term screening in our laboratory, which has a good antagonistic effect on a variety of plant pathogenic bacteria. In this study, we investigated the efficacy and bacterial inhibition of B. laterosporus SN19-1 against BLB to lay the theoretical foundation and research technology for the development of SN19-1 as a biopesticide of BLB. It was found that SN19-1 has the ability to fix nitrogen, detoxify organic phosphorus, and produce cellulase, protease, and siderophores, as well as IAA. In a greenhouse pot experiment, the control efficiency of SN19-1 against BLB was as high as 90.92%. Further investigation of the inhibitory mechanism of SN19-1 on Xoo found that the biofilm formation ability of Xoo was inhibited and the pathogenicity was weakened after the action of SN19-1 sterile supernatant on Xoo. The activities of enzymes related to respiration and the energy metabolism of Xoo were significantly inhibited, while the level of intracellular reactive oxygen species was greatly increased. Scanning electron microscopy observations showed folds on the surface of Xoo. A significant increase in cell membrane permeability and outer membrane permeability and a decrease in cell membrane fluidity resulted in the extravasation of intracellular substances and cell death. The results of this study highlight the role of B. laterosporus SN19-1 against the pathogen of BLB and help elucidate the underlying molecular mechanisms.

Anti-Salmonella Activity of a Novel Peptide, KGGDLGLFEPTL, Derived from Egg Yolk Hydrolysate

The present study aimed to characterize the mode of action of a novel antimicrobial peptide isolated from egg yolk hydrolysate. The EYHp6, KGGDLGLFEPTL, exhibited inhibition against Salmonella enterica serovar Typhimurium TISTR 292 and S. enterica serovar Enteritidis DMST 15679 with a MIC value of 2 mM. In contrast, S. enterica serovar Newport ATCC 6962 and other strains of Typhimurium and Enteritidis were inhibited at 4 mM. EYHp6 increased the cell membrane permeability of S. Typhimurium TISTR 292, leading to DNA leakage. Membrane integrity determined by propidium iodide and SYTO9 staining visualized by confocal microscopy demonstrated that EYHp6 at 1 × MIC induced disruption of cell membranes. Electron microscopy revealed that treatment of S. Typhimurium with EYHp6 led to damage to the cell membrane, causing the leakage of intracellular contents. Synchrotron-based Fourier-transform infrared spectroscopy indicated that EYHp6 killed S. Typhimurium by targeting fatty acids and nucleic acids in the cell membrane. The peptide did not show hemolytic activity up to 4 mM. These findings suggest that EYHp6 could be a promising antibacterial agent for controlling the growth of S. enterica.

Laterosporulin25: A probiotically produced, novel defensin-like bacteriocin and its immunogenic properties

Although multiple vaccines have been developed against infectious diseases, the rapid emergence of new pathogens develops an urgent need for novel strategies to combat infectious diseases. Antimicrobial peptides (AMPs) are excellent agents to fight against infectious diseases having unique multiple mechanisms of action against various pathogens. Apart from the direct applications, AMPs can also be developed as subunit vaccines or could be used as a highly immunogenic carrier protein with highly antigenic but non-immunogenic antigens. Here in the present study, we have identified a novel defensin-like bacteriocin, laterosporulin25 (LS25) upon genome mining of Brevibacillus laterosporus DSM25, a probiotic bacterial strain. By using immunoinformatic tools, we have studied the immunogenic and physiochemical properties of LS25. LS25 is characterized as defensin-like bacteriocin, having 51 amino acids and a molecular weight of 5862.7 Da. The modeled tertiary structure of LS25 is docked with TLR3 and TLR4-MD2 complex to confirm the facilitation of induced immune response that is further validated using molecular dynamics simulations and In-silico immune stimulations. Overall, detailed immunoinformatics analysis suggested LS25 as a potential candidate to be used as an adjuvant or carrier protein for subunit vaccine development, however, further in-vitro and in-vivo experiments are essential to validate its potential.

Underexplored bacteria as reservoirs of novel antimicrobial lipopeptides

Natural products derived from microorganisms play a prominent role in drug discovery as potential anti-infective agents. Over the past few decades, lipopeptides produced by particularly Bacillus, Pseudomonas, Streptomyces, Paenibacillus, and cyanobacteria species, have been extensively studied for their antimicrobial potential. Subsequently, daptomycin and polymyxin B were approved by the Food and Drug Administration as lipopeptide antibiotics. Recent studies have however, indicated that Serratia, Brevibacillus, and Burkholderia, as well as predatory bacteria such as Myxococcus, Lysobacter, and Cystobacter, hold promise as relatively underexplored sources of novel classes of lipopeptides. This review will thus highlight the structures and the newly discovered scaffolds of lipopeptide families produced by these bacterial genera, with potential antimicrobial activities. Additionally, insight into the mode of action and biosynthesis of these lipopeptides will be provided and the application of a genome mining approach, to ascertain the biosynthetic gene cluster potential of these bacterial genera (genomes available on the National Center for Biotechnology Information) for their future pharmaceutical exploitation, will be discussed.

Antibacterial Regularity Mining Beneath the Systematic Activity Database of Lipopeptides Brevilaterins: An Instructive Activity Handbook for Its Food Application

Bacterial contamination is a primary threat to food safety. Therefore, the persistent development of natural antibacterial agents has become essential work. The present essay attempts to establish a systematic antibacterial activity database to instruct the food application of brevilaterins, promising antibacterial lipopeptides from Brevibacillus laterosporus S62-9. Minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were systematically collected from 43 species of standard bacteria and 140 strains of isolated bacteria (food spoilage bacteria and antibiotic-resistant bacteria) using a broth dilution method. The results showed that brevilaterins performed a broad-spectrum inhibitory (0.5~128 μg/mL) and bactericidal activity (1~256 μg/mL), especially efficient against Gram-positive bacteria and spoilage bacteria from grain products. Moreover, brevilaterins not only inhibit and kill multiple antibiotic-resistant bacteria but do not readily develop resistance, with a small specific value of MBC/MIC (1~8). Furthermore, brevilaterins would interact with negatively charged sodium dodecyl sulfate and bind amphipathic soybean phospholipid with an affinity constant of K_D = 4.70 × 10⁻⁴ M. No significant activity difference was found between brevilaterin B and brevilaterin C. Collectively, this work contributed rich antibacterial data of brevilaterins and revealed the antibacterial regularity beneath these data, which can be used as an activity handbook to instruct their application in food safety.

An accurate strategy for pointing the key biocatalytic sites of bre2691A protein for modification of the brevilaterin from Brevibacillus laterosporus

BACKGROUND

Brevilaterin A-E, a novel class of multi-component cationic antimicrobial lipopeptides, were biosynthesized by a non-ribosomal peptides synthetase (NRPS) in Brevibacillus laterosporus. However, the antimicrobial abilities of different brevilaterin components varied greatly, and this multi-component form was impeding the scale production of the excellent component, and a little information about the brevilaterin biosynthesis mechanism was available to apply in brevilaterin design modification. In this study, we used an accurate strategy that revealed the reason for producing multi-component was the substrate selectivity of bre2691A protein being not enough specific and pinpointed the key design sites to make the specificity of bre2691A enhanced.

RESULTS

Bioinformatic analysis revealed that the biocatalytic site of bre2691A, which was an adenylation domain catalyzed and recognized methionine, leucine, valine and isoleucine and thus introduced them into brevilaterins and caused different components (brevilaterin A-E), was consisted of A1 ~ A10 residues named specificity-conferring code. Coupling molecular docking simulations with mutation studies identified A2 and A7 as critical residues, where determined substrate-specificity and impacted activity. The in virto activity assay showed that the A2 mutant (G193A) would lose activity against methionine and have no effect on the other three amino acids, the A7 mutant (G285C) would enhance the catalytic activity against four substrates, especially against leucine at almost a double activity. When the A2 and A7 residues were synchronously mutated, this mutant would be more focused on recognizing leucine.

CONCLUSIONS

An accurate strategy that combined with bioinformatics and site-directed mutation techniques revealed the pivotal site A2 and A7 positions of bre2691A protein that could be used to design and modify brevilaterins, thus further providing a reasonable direction of genetic engineering for Brevibacillus laterosporus. A deeper understanding of the function of crucial residues in the adenylation domain would make it get more accurate and highly efficient design and more fully utilized. Furthermore, it would contribute to biotechnological applications, namely for the large centralized synthesis of antimicrobial peptides, or for the optimization of their production.

Structural Organization of Brevilaterin Biosynthesis in Brevibacillus laterosporus S62-9: A Novel MbtH-Independent Cationic Antimicrobial Peptide Synthetase System

Cationic antimicrobial peptides, produced by nonribosomal peptide synthetases (NRPSs), have received great attention in different applications, including as biocontrol and antimicrobial agents against foodborne pathogenic bacteria. Also, Brevibacillus spp. is a competent microorganism to produce cationic antimicrobial peptides yet has received little attention. Herein, Brevibacillus laterosporus S62-9 genome mining revealed an integrated cationic antimicrobial peptide synthetase system that synthesized brevilaterin. Combining biochemical analysis with bioinformatics elucidated that the A domain from this system was the MbtH-independent enzyme and showed activity against the same amino acid in the structure of brevilaterin. Moreover, the creations of the first three and position 12 residues in the sequence were targeted to bre261, bre270, bre2691A, and bre2662, respectively. Further analysis of the specificity-conferring code of the A domain suggested that a tiny difference would make the activity of the A domain very diverse and the range of substrate selection would be enlarged or narrowed by changing some residues in the code. The dissection of this biosynthesis mechanism would contribute to the successful realization of reasonable artificial design and the modification of bioactive peptides, and this capable organism also would be more fully utilized.