Discovery of novel antimicrobial peptides, Brevilaterin V, from Brevibacillus laterosporus S62-9 after regulated by exogenously-added L-valine

Senegalin-2: A Novel Hexadecapeptide from Kassina senegalensis with Antibacterial and Muscle Relaxant Activities, and Its Derivative Senegalin-2BK as a Bradykinin Antagonist

The amphibian skin secretions are excellent sources of bioactive peptides, some of which and their derivatives exhibit multiple properties, including antibacterial and antagonism against bradykinin. A novel peptide Senegalin-2 was isolated from the skin secretions of Kassina senegalensis frog. Senegalin-2 relaxed rat bladder smooth muscle (EC50 17.94 nM) and ileum smooth muscle (EC50 135 nM), inhibited S. aureus and MRSA at 2 μM, and exhibited low hemolytic activity with no cytotoxicity. To design effective bradykinin antagonists, Senegalin-2 was conjugated with bradykinin to synthesize Senegalin-2BK. This modification retained potent activity against Gram-positive bacteria. Compared to Senegalin-2, Senegalin-2BK significantly reduced hemolysis and exhibited a more than threefold increase in the selectivity index. Furthermore, Senegalin-2BK contracted the bladder (EC50 2.83 μM) and ileum (EC50 56.64 nM)'s smooth muscle. The pretreatment with 10-7 M Senegalin-2BK reduced the 10-6 M bradykinin contraction on the bladder by over 70%. In conclusion, Senegalin-2 has dual functionalities as an antibacterial agent and muscle relaxant, positioning it as a potential therapeutic candidate for managing overactive bladder. As a synthetically derived bradykinin antagonist and myotropic peptide with antibacterial properties, Senegalin-2BK shows promise in effective therapies for relieving pain, inflammation, and addressing muscular disorders such as urinary retention, constipation, and infections.

Synthesis and structure-activity study of the antimicrobial lipopeptide brevibacillin

The antimicrobial lipopeptide brevibacillin is a non-ribosomally synthesized peptide produced by Brevibacillus laterosporus with inhibitory activity against several clinically relevant Gram-positive pathogenic bacteria such as Staphylococcus aureus, Listeria monocytogenes, and Clostridium difficile. In this study, we report the total synthesis of brevibacillin and analogues thereof as well as structure-activity relationship and cytotoxicity studies. Several novel synthetic analogues exhibited high inhibitory activities with minimal inhibitory concentration values in the low micromolar range against several bacteria including Gram-positive L. monocytogenes, S. aureus, Enterococcus faecalis, and Clostridium perfringens as well as Gram-negative Campylobacter coli and Pseudomonas aeruginosa. Of particular interest, four analogues showed a broad spectrum of action and greater antimicrobial activity versus cytotoxicity ratios than native brevibacillin. With a more accessible and efficient production process and improved pharmacological properties, these synthetic analogues are promising candidates to prevent and control the proliferation of various pathogens in the food industry as well as veterinary and human medicine.

Gut bacterium Burkholderia cepacia (BsNLG8) and immune gene Defensin A contribute to the resistance against Nicotine-induced stress in Nilaparvata lugens (Stål)

Nicotine, a naturally occurring alkaloid found in tobacco, is a potent neurotoxin extensively used to control Nilaparvata lugens (Stål), a destructive insect pest of rice crops. The insect gut harbors a wide array of resident microorganisms that profoundly influence several biological processes, including host immunity. Maintaining an optimal gut microbiota and immune homeostasis requires a complex network of reciprocal regulatory interactions. However, the underlying molecular mechanisms driving these symbiotic exchanges, particularly between specific gut microbe and immunity, remain largely unknown in insects. Our previous investigations identified and isolated a nicotine-degrading Burkholderia cepacia strain (BsNLG8) with antifungal properties. Building on those findings, we found that nicotine intake significantly increased the abundance of a symbiotic bacteria BsNLG8, induced a stronger bacteriostatic effect in hemolymph, and enhanced the nicotine tolerance of N. lugens. Additionally, nicotine-induced antimicrobial peptides (AMPs) exhibited significant antibacterial effects against Staphylococcus aureus. We adopted RNA-seq to explore the underlying immunological mechanisms in nicotine-stressed N. lugens. Bioinformatic analyses identified numerous differentially expressed immune genes, including recognition/immune activation (GRPs and Toll) and AMPs (i.e., Defensin, Lugensin, lysozyme). Temporal expression profiling (12, 24, and 48 hours) of immune genes revealed pattern recognition proteins and immune effectors as primary responders to nicotine-induced stress. Defensin A, a broad-spectrum immunomodulatory cationic peptide, exhibited significantly high expression. RNA interference-mediated silencing of Defensin A reduced the survival, enhanced nicotine sensitivity of N. lugens to nicotine, and decreased the abundance of BsNLG8. The reintroduction of BsNLG8 improved the expression of immune genes, aiding nicotine resistance of N. lugens. Our findings indicate a potential reciprocal immunomodulatory interaction between Defensin A and BsNLG8 under nicotine stress. Moreover, this study offers novel and valuable insights for future research into enhancing nicotine-based pest management programs and developing alternative biocontrol methods involving the implication of insect symbionts.

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.

Novel Property Cytotoxicity and Mechanism of Food Preservative Brevilaterins against Human Gastric Cancer Cells

Brevilaterins, antimicrobial peptides produced by Brevibacillus laterosporus, are regarded as excellent food preservatives and are popular as antimicrobial applications. Recent research has uncovered their potent cytotoxic effects against diverse cancer cells, thereby underscoring the pressing need for more extensive and intensive investigations into this use. In this study, we explored their novel function in inducing cytotoxicity to cancer cells and systematically investigated the mechanism of action of Brevilaterin B/C (BB/BC) in vivo. Proliferation, membrane permeability, and apoptotic rate were evaluated using CCK-8 assay, LDH assay, and Annexin V-FITC/PI kits. ROS levels and mitochondrial membrane potential were detected using the fluorescent probe DCFH-DA and JC-1. Our results demonstrated that both BB and BC at concentrations of 4-6 µg/mL significantly inhibited the proliferation and migration of gastric cancer cells BGC-823. Treatment with 4 µg/mL of BB/BC rapidly increased LDH levels in the supernatant of BGC-823 cells, leading to further investigation of the mechanism of apoptosis. We found that the apoptotic rate of BGC-823 cells significantly increased upon treatment with BB/BC, demonstrating their potent induction of apoptosis. BB/BC-induced ROS production in BGC-823 cells impaired their growth and induced apoptosis, indicating a close association between apoptosis and ROS elevation. Additionally, JC-1 aggregates rapidly accumulated after treatment with 4 µg/mL of BB/BC, suggesting changes in mitochondrial membrane potential and early apoptosis. Taken together, our findings revealed that BB and BC exhibit significant anticancer effects against gastric cancer cells, highlighting the promising potential of Brevilaterins as anticancer agents.

Purification and Characterization of Novel Anti-MRSA Peptides Produced by Brevibacillus sp. SPR-20

Methicillin-resistant Staphylococcus aureus (MRSA) is listed as a high-priority pathogen because its infection is associated with a high mortality rate. It is urgent to search for new agents to treat such an infection. Our previous study isolated a soil bacterium (Brevibacillus sp. SPR-20), showing the highest antimicrobial activity against S. aureus TISTR 517 and MRSA strains. The present study aimed to purify and characterize anti-MRSA substances produced by SPR-20. The result showed that five active substances (P1-P5) were found, and they were identified by LC-MS/MS that provided the peptide sequences of 14-15 residues. Circular dichroism showed that all peptides contained β-strand and disordered conformations as the major secondary structures. Only P1-P4 adopted more α-helix conformations when incubated with 50 mM SDS. These anti-MRSA peptides could inhibit S. aureus and MRSA in concentrations of 2-32 μg/mL. P1 (NH₂-VVVNVLVKVLPPPVV-COOH) had the highest activity and was identified as a novel antimicrobial peptide (AMP). The stability study revealed that P1 was stable in response to temperature, proteolytic enzymes, surfactant, and pH. The electron micrograph showed that P1 induced bacterial membrane damage when treated at 1× MIC in the first hour of incubation. The killing kinetics of P1 was dependent on concentration and time. Mechanisms of P1 on tested pathogens involved membrane permeability, leakage of genetic material, and cell lysis. The P1 peptide at a concentration up to 32 μg/mL showed hemolysis of less than 10%, supporting its safety for human erythrocytes. This study provides promising anti-MRSA peptides that might be developed for effective antibiotics in the post-antibiotic era.

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.

Brevilaterin B from Brevibacillus laterosporus has selective antitumor activity and induces apoptosis in epidermal cancer

Brevilaterins as antimicrobial peptides (AMPs) secreted by a newly discovered species Brevibacillus laterosporus, had been demonstrated to display excellent antibacterial and antifungal activities; however, very limited information about their new bioactivity was ever developed. Herein, we discovered Brevilaterin B, an AMP produced by Br. laterosporus S62-9, exhibited a new anticancer activity and investigated its anticancer details. Proliferation, membrane permeability and apoptotic rate of cell lines were studied by methods of CCK-8 Assay, LDH Assay and Annexin V-FITC/PI Kits, respectively. ROS levels and mitochondrial membrane potential of tested cells were further detected through the fluorescent probes DCFH-DA and JC-1. Brevilaterin B exhibited broad-spectrum anticancer activity in a dose-dependent manner. It selectively inhibited the proliferation of epidermal cancer cell A431 but had no effect on its control normal cells in a dose of 2.0 µg/mL. In comparision, typical morphological characteristics of apoptosis and an apoptotic ratio of 71.0% in A431 were observed after treatment by 2.0-3.0 µg/mL of Brevilaterin B. The ROS levels increased by 21.3% and mitochondrial membrane potential reduced by 48.8% from A431 were further occurred, indicating Brevilaterin B's anticancer action was mainly focus on the mitochondrion of cancer cells. In total, Brevilaterin B we reported above maybe believed to be a potential application as an anticancer medicament, increasing its commercial value.

Broad-spectrum cytotoxicity to cancer cells of Brevilaterin C from Brevibacillus laterosporus and its specific mechanism on human epidermal cancer cells

Antimicrobial peptides (AMP) from Brevibacillus laterosporus have good prospects as clinical treatments for cancer. Nevertheless, details about their anticancer spectrum and mode of cytotoxicity remain poorly understood. A newly found AMP (named Brevilaterin C) secreted by B. laterosporus S62-9 exhibited strong inhibition on almost cancer cell lines examined at a concentration of 8 µg/ml but was relatively safe for normal cells. We further systematically examined its cytotoxicity and mechanism toward human epidermal cancer cell A431. A dosage of 3 µg/ml of Brevilaterin C could significantly increase lactate dehydrogenase release of tumor cells. Moreover, it could remarkably increase the ratio of apoptosis and reactive oxygen species generation of A431, indicating effective induction of apoptosis. Moreover, the formation of JC-1 aggregates was effectively prevented by a low concentration of Brevilaterin C, indicating its effective induction of A431's apoptosis. Brevilaterin C exhibited broad-spectrum cytotoxicity to cancer cells, indicating a good potential prospect in the medical field.