Abstract Discovering more novel antimicrobial compounds has become an keen research problem. In this study, YA215 genome was sequenced by the Illumina HiSeq + PacBio sequencing platform. Genome assembly was performed by Unicycler software and the gene clusters responsible for secondary metabolite biosynthesis were predicted by antiSMASH. The genome comprised 3976514 bp and had a 46.56% G + C content. 3809 coding DNA sequences, 27 rRNAs, 86 tRNAs genes and 79 sRNA were predicted. Strain YA215 was re-identified as Bacillus velezensis based on ANI and OrthoANI analysis. In the COG database, 23 functional groups from 3090 annotations were predicted. In the GO database, 2654 annotations were predicted. 2486 KEGG annotations linked 41 metabolic pathways. Glycosyl transferases, polysaccharide lyases, auxiliary activities, glycoside hydrolases, carbohydrate esterases and carbohydrate-binding modules were predicted among the 127 annotations in the CAZy database. AntiSMASH analysis predicted that strain B. velezensis YA215 boasted 13 gene clusters involved in synthesis of antimicrobial secondary metabolites including surfactin, fengycin, macrolactin H, bacillaene, difficidin, bacillibactin, bacilysin, and plantazolicin. Three of the gene clusters (gene cluster 5, gene cluster 9 and gene cluster 10) have the potential to synthesize unknown compounds. The research findings have the potential to contribute significantly to the development of natural novel compounds with antimicrobial activity in B. velezensis YA215.
Foodborne illnesses have a significant impact on global human health, prompting increased attention in the quest for potential antimicrobial agents against foodborne pathogens. This study delves into the antibacterial mechanism of C12surfactin against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), exploring its potential application as a food preservative. The results reveal remarkable antibacterial efficacy of C12surfactin against both E. coli (minimum inhibitory concentration (MIC) = 7.5 µg/mL, minimal bactericidal concentration (MBC) = 30 µg/mL) and S. aureus (MIC = 1.87 µg/mL, MBC = 7.5 µg/mL). Furthermore, C12surfactin demonstrates robust stability against proteases, as well as under varying thermal and pH conditions and shows low toxicity. The study also finds that C12surfactin induced a reduction in cell metabolic activity, an elevation in reactive oxygen species (ROS) production, disruption of cell membrane permeability and integrity, and triggers the leakage of nucleic acids and proteins. Gel retardation experiments show that C12surfactin could bind to the genomic DNA of E. coli, resulting in the disruption of DNA structure. Additionally, molecular docking results show that C12surfactin targets enzymes associated with peptidoglycan and DNA synthesis and interacts with Mur enzymes (MurC, MurD, MurE, MurF, and MurG), dihydrofolate reductase (DHFR), and DNA gyrase through hydrogen bonding, hydrophobic interactions, and salt-bridging. Lastly, during milk storage, C12surfactin treatment results in a reduction in the number of E. coli and S. aureus cells. These findings strongly suggest that C12surfactin holds promise as a potential candidate for development as a food preservative or antibacterial agent.
The increasing burden and health risks of antimicrobial resistance (AMR) pose a great threat to society overall. Lipopeptides exhibit great potential as novel and safe alternatives to traditional antibiotics. In this study, the strain YA215, which was isolated from the mangrove area in Beibu Gulf, Guangxi, China, was identified as Bacillus velezensis. Then, YA215 lipopeptide extracts (YA215LE) from B. velezensis was found to exhibit a wide spectrum of antibacterial and antifungal activities. Additionally, YA215LE was identified and found to contain three groups of lipopeptides (surfactin, iturin, and fengycin). Furthermore, one separation fraction (BVYA1) with significant antibacterial activity was obtained. Additionally, liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis of BVYA1 showed three molecular ion peaks ([M + H]+: m/z 980.62; 994.66; 1008.66) corresponding to conventional surfactin homologs. By MS/MS analysis, BVYA1 was identified as sufactin with the precise amino acid sequence Glu-Leu/Ile-Leu-Val-Asp-Leu-Leu/Ile and hydroxyl fatty acids with 11-13 carbons. [M + H]+ at m/z 980.62 was detected for the first time in B. velezensis, which demonstrates that the strain corresponds to a new surfactin variant. In particular, BVYA1 showed antibacterial activity with the minimum inhibitory concentration (MIC) values of 7.5-15 μg/ml. Finally, the preliminary mechanism of inhibiting E. coli treated with BVYA1 showed that BVYA1 effectively permeabilized the cytoplasmic membrane and disrupted the morphology of targeted bacterial cells. In conclusion, this study suggests that the YA215LE from B. velezensis YA215 might be a potential candidate for a bactericide.
Scanning and transmission electron microscopy were used to characterize the morphology of the carbon microcoils (CMCs). The Raman spectra showed that CMCs had local regular structure as ID/IG = 0.841. Then, aligned CMCs/silicone–rubber composites (5 × 5 × 1 mm3) were fabricated by coating of silicone rubber on the CMCs. Their alternating current impedance characteristics were measured as a function of applied load and the pressure sensitivity was discussed. The results showed that the impedance decreased as the increasing applied load, and the sample with less CMCs owned high pressure sensitivity, which indicated a novel composite film could act as an alternative of tactile sensor.
Abstract Antibiotics are essential for combating pathogens; however, their misuse has led to increased resistance, necessitating the search for effective, low-toxicity alternatives. Surfactin, due to its unique structure, exhibits significant antibacterial activity without easily inducing resistance, making it a focus of current research. Nonetheless, the effects of branched-chain amino acids (BCAAs) on surfactin's structure and activity are not well understood. This study examines the influence of BCAAs (L-valine, L-leucine, and L-isoleucine) on the lipopeptide (surfactin) produced by B. velezensis YA215. Process optimization revealed that adding 1 g/L of L-Leu and L-Ile, and 0.5 g/L of L-Val, maximizes surfactin production. Surfactin levels peaked with L-Val and L-Ile at 36 h, while L-Leu reached its maximum at 24 h. Notably, L-Val supplementation resulted in the highest relative surfactin content. Antimicrobial testing demonstrated that BCAAs significantly enhance the antibacterial effects of lipopeptides against Escherichia coli and Staphylococcus aureus, with Val showing the most pronounced effect. The addition of BCAAs notably altered the composition of surfactin fatty acid chains. Specifically, Val increased the proportions of iso C14 and iso C16 β-hydroxy fatty acids from 13.3% and 4.216–23.803% and 8.31%, respectively. Additionally, the amino acid composition at the 7th position of the peptide chain changed significantly, especially with Val addition, which increased the proportion of C14 [Val 7] surfactin by 3.29 times. These structural changes are likely associated with the enhanced antibacterial activity of surfactin. These findings provide valuable insights into the roles of BCAAs in microbial fermentation, underscoring their importance in metabolic engineering to enhance the production of bioactive compounds.
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