Bacillomycin D-C16 inhibits growth of Fusarium verticillioides and production of fumonisin B1 in maize kernels

Antifungal Activity and Mechanism of Diaporthein B against Botryosphaeria dothidea in Prevention of Apple Ring Rot

Apple ring rot, caused by the pathogenic fungus Botryosphaeria dothidea, has inflicted substantial economic losses and caused significant food safety concerns. In this study, a pimarane-type diterpenoid, diaporthein B (DTB), isolated from a marine-derived fungus, exhibited significant antifungal activity against B. dothidea, with an EC50 value of 8.8 μg/mL. Transcriptome, metabolome, and physiological assays revealed that DTB may target mitochondria and disrupt the tricarboxylic acid (TCA) cycle and oxidative phosphorylation processes. This interference led to increased accumulation of reactive oxygen species and subsequent lipid peroxidation, ultimately inhibiting fungal growth. Furthermore, DTB exhibited an inhibitory potency against apple ring rot at a concentration of 31.2 μg/mL, achieving rates ranging from 67.7 to 81.6% across four distinct apple cultivars. These results indicated that DTB could serve as a novel fungicide for controlling apple ring rot in apple cultivation, transportation, and storage.

Phenotypic and Genomic Characterization of Pseudomonas wuhanensis sp. nov., a Novel Species with Promising Features as a Potential Plant Growth-Promoting and Biocontrol Agent

Plant growth-promoting rhizobacterial strain FP607T was isolated from the rhizosphere of beets in Wuhan, China. Strain FP607T exhibited significant antagonism toward several phytopathogenic bacteria, indicating that FP607T may produce antimicrobial metabolites and has a stronger biocontrol efficacy against plant pathogens. Growth-promoting tests showed that FP607T produced indole-3-acetic acid (IAA), NH3, and ferritin. The genome sequence of strain FP607T was 6,590,972 bp long with 59.0% G + C content. The optimum temperature range was 25-30 °C, and the optimum pH was 7. The cells of strain FP607T were Gram-negative, short, and rod-shaped, with polar flagella. The colonies on the King's B (KB) agar plates were light yellow, smooth, and circular, with regular edges. A phylogenetic analysis of the 16S rRNA sequence and a multilocus sequence analysis (MLSA) showed that strain FP607T was most closely related to the type of strain Pseudomonas farris SWRI79T. Based on a polyphasic taxonomic approach, strain FP607T was identified as a novel species within the genus Pseudomonas, for which the name Pseudomonas wuhanensis sp. nov. was proposed. The type of strain used was FP607T (JCM 35688, CGMCC 27743, and ACCC 62446).

Bacillus atrophaeus NX-12 Utilizes Exosmotic Glycerol from Fusarium oxysporum f. sp. cucumerinum for Fengycin Production

Bacillus strains are widely used as biological control agents to protect plants from fungal pathogens. However, whether Bacillus can exploit fungal pathogens to increase its biocontrol efficacy remains largely unexplored. Here, Bacillus atrophaeus NX-12 showed a high inhibition efficacy against Fusarium oxysporum f. sp. cucumerinum (FOC). The primary extracellular antifungal component of B. atrophaeus NX-12 was identified as fengycin by matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry (MALDI-TOF-MS) analysis. NX-12-secreted fengycin not only inhibited the germination of FOC spores but also induced the production of reactive oxygen species (ROS) in FOC cells, leading to oxidative stress and the accumulation of glycerol. Additionally, NX-12-secreted fengycin increased FOC cell wall hydrolase activity, leading to cell splitting and the exosmose of accumulated glycerol. The increased exosmose of glycerol further promoted the production of fengycin. Our results showed that in addition to the direct inhibition of FOC, NX-12 can indirectly strengthen its antagonistic efficacy against the pathogen by exploiting the exosmotic glycerol from FOC.

Effects of the deletion and substitution of thioesterase on bacillomycin D synthesis

OBJECTIVES

The importance of thioesterase domains on bacillomycin D synthesis and the ability of different thioesterase domains to selectively recognize and catalyze peptide chain hydrolysis and cyclization were studied by deleting and substituting thioesterase domains.

RESULTS

No bacillomycin D analogs were found in the thioesterase-deleted strain fmbJ-ΔTE, indicating that the TE domain was essential for bacillomycin D synthesis. Then the thioesterase in bacillomycin D synthetases was replaced by the thioesterase in bacillomycin F, iturin A, mycosubtilin, plipastatin and surfactin synthetases. Except for fmbJ-S-TE, all others were able to synthesize bacillomycin D homologs because a suitable recombination site was selected, which maintained the integrity of NRPSs. In particular, the yield of bacillomycin D in fmbJ-IA-TE, fmbJ-M-TE and fmbJ-P-TE was significantly increased.

CONCLUSION

This study expands our understanding of the TE domain in bacillomycin D synthetases and shows that thioesterase has excellent potential in the chemical-enzymatic synthesis of natural products or their analogs.

Insights into Antifungal Mechanisms of Bacillus velezensis S141 against Cercospora Leaf Spot in Mungbean (V. radiata)

Cercospora leaf spot (CLS) is caused by Cercospora canescens and is one of the most important diseases of mungbean (Vigna radiata). Cercospora leaf spot may result in economic loss in production areas. The present study investigated the potential of Bacillus velezensis S141 as a biocontrol agent for C. canescens PAK1 growth on culture plates. Cell-free secretions from a dual culture of S141+PAK1 inhibited fungal growth more than those from a single culture of S141. The biocontrol efficiency of S141 against Cercospora leaf spot on mungbean was then evaluated by spraying. The disease severity of Cercospora leaf spot was significantly reduced in plants treated with S141, with a control efficiency of 83% after 2 days of infection. Comparative transcriptomics and qRT-PCR ana-lyses of S141 during C. canescens inhibition were performed to elucidate the antifungal mechanisms underlying its antifungal activity against Cercospora leaf spot. According to the differentially expressed genes, most up-regulated genes involved in the biosynthetic genes encoding enzymatic hydrolases, including protease, β-glucanase, and N-acyl glucosaminase, were detected in strain S141 following its interaction. Moreover, genes related to secondary metabolites (surfactin, bacilysin, and bacillomycin D) were up-regulated. Collectively, these results suggest that S141 exhibited strong antifungal activity against C. canescens due to multiple enzymatic hydrolases and secondary metabolites. Therefore, the present study provides insights into the biological network responsible for the antifungal activity of B. velezensis S141 against C. canescens.

Anti-toxicogenic fungi and toxin-reducing effects of bacillomycin D in combination with fungicides

Mycotoxins are toxic secondary metabolites produced by fungus including Aspergillus and Fusarium. They can contaminate food and cause major health issues. Bacillomycin D (BD) is a natural antimicrobial lipopeptide generated by Bacillus that has excellent antifungal capabilities, but its high price prevents it from being widely used. Chemically produced and essential oil-based fungicides are also currently the most frequent types. In the study, the effects of combining BD with two types of fungicides on the growth of toxicogenic fungi as well as the generation of deoxynivalenol (DON) and fumonisin B₁ (FB₁) were examined. It was discovered that BD was more effective in suppressing molds than the other two types of fungicides, and it could be combined with synthetic or essential oil-based fungicides to provide a synergistic or additive effect. BD 31.25 μg/mL + Thymol (Thy) 7.81 μg/mL and BD 11.45 μg/mL + Cinnamon oil (Cin) 3.90 μg/mL inhibited F. graminearum, respectively. The combination of BD+Thy and BD+Cin at this concentration considerably reduced 60%-80% spore germination, when DON dropped below 300 ng/L. Furthermore, both combinations suppressed F. moniliforme growth and FB₁ synthesis in a dose-dependent manner at lower concentrations. At an action dose of 2 MIC, FB₁ production might be reduced to less than 100 ng/L. Our findings indicated that BD might interact synergistically with various fungicides, suggesting that it could be useful in the field of antifungal and toxicity reduction in food.

Antifungal Mechanism of MTE-1, a Novel Oligosaccharide Ester, against Ustilaginoidea virens

Ustilaginoidea virens is a pathogenic fungus that causes false smut disease in rice during the flowering stage through stamen filaments. Currently, there is a need to develop safe and effective antifungal agents for the control of this disease. In our preliminary experiments, we found that MTE-1, a new trisaccharide ester, exhibits significant inhibitory activity against U. virens. Hence, the effects and inhibitory mechanism of MTE-1 in U. virens were investigated. Results showed that the MTE-1 inhibited the hyphae growth of U. virens with an IC₅₀ of 5.67 μg/mL. Similarly, MTE-1 disrupted the endomembrane system in U. virens, especially the plasma membrane, mitochondria, and lipidosome. Moreover, transcriptome and proteome analysis indicated that MTE-1 inhibited the growth of U. virens by inhibiting the synthesis of lipids, altering the primary metabolic pathways including carbohydrates and amino acid metabolism, and affecting the intracellular redox dyshomeostasis, thus leading to the disorder of active oxygen metabolism. These findings lay the foundation for the future application of MTE-1-derived agents in the management of antifungal diseases.