Bacillus amyloliquefaciens XJ-BV2007 produces lipopetides that significantly inhibit Alternaria alternata and tenuazonic acid accumulation in processing tomatoes

Black spot disease in tomatoes, caused by Alternaria sp, results in the contamination of the tomatoes with Alternaria mycotoxins, especially tenuazonic acid (TeA). In this regard, TeA accumulation in processing tomatoes and their derived food products represent a serious health hazard. In this regard, our previous study provided evidence that lipopeptides produced by Bacillus amyloliquefaciens XJ-BV2007 effectively inhibit A. alternata and TeA accumulation. In the present study, we significantly increased the production of lipopeptides by optimizing the composition of the culture medium and the fermentation conditions utilizing single-experiments and response surface methodology. The optimal medium (6.0 g/L maltose, 9.0 g/L peptone, and 5.0 g/L yeast extract) and fermentation protocol (4.5 % starter inoculation volume and 44 h of fermentation at 33 °C) increased the yield of lipopeptides by 111 %. Spraying field-planted tomato plants with lipopeptides at 10day intervals decreased the incidence of black spot disease in tomato fruit and the level of TeA mycotoxin. Notably, the expression level of AaTAS1, which encodes TeA, was substantially downregulated in diseased tomatoes. A molecular docking model indicated that the lipopeptide fengycin has a strong binding potential with TeA. Results of the study provide a foundation for further exploring the use of B. amyloliquefaciens XJ-BV2007 and/or its lipopeptides as biopesticides for the control of black spot disease and prevention of TeA contamination in processing tomato products.

Sustainable microbial solutions for managing fungal threats in wheat: progress and future directions

Biotrophic and necrotrophic fungi are responsible for causing a range of diseases in wheat, resulting in significant economic losses and a decline in quality. Effective management of these diseases generally involves a combination of resistance breeding, chemical treatments, and cultural practices. However, traditional breeding methods have made limited progress due to the slow pace of genetic improvements, the complexity of the wheat genome, and the quantitative nature of disease resistance traits, along with the constantly evolving virulence of pathogens. This situation has prompted research into more effective and eco-friendly alternatives, such as biological control. Recent studies have concentrated on using antagonistic microbes to decrease the reliance on chemical pesticides while enhancing wheat health and productivity. A comprehensive overview of current knowledge on wheat disease outbreaks is being developed, with a focus on advancements in biological control strategies. The review will first discuss the key fungal pathogens and their associated diseases, followed by a summary of biological control methods, particularly emphasizing potential microbial antagonists. Additionally, it will explore strategies to improve the efficacy of biocontrol agents, which are crucial for a holistic and sustainable approach to wheat disease management. Ultimately, the article will highlight the role of biological control in promoting more sustainable agricultural practices, particularly concerning wheat diseases, in alignment with the UN sustainable development goals.

Hybrid de novo whole genome assembly of lipopeptide producing novel Bacillus thuringiensis strain NBAIR BtAr exhibiting antagonistic activity against Sclerotium rolfsii

Bacillus thuringiensis Berliner is recognized as a predominant bioinsecticide but its antifungal potential has been relatively underexplored. A novel B. thuringiensis strain NBAIR BtAr was isolated and morphologically characterized using light and scanning electron microscopy, revealing presence of bipyramidal, cuboidal, and spherical parasporal crystals. The crude form of lipopeptides was extracted from NBAIR BtAr and assessed for its antagonistic activity in vitro, and demonstrated 100 % inhibition of Sclerotium rolfsii Sacc. at a minimum inhibitory concentration of 50 μL of the crude lipopeptide extract per mL of potato dextrose agar. To identify the antagonistic genes responsible, we performed whole genome sequencing of NBAIR BtAr, revealing the presence of circular chromosome of 5,379,913 bp and 175,362 bp plasmid with 36.06 % guanine-cytosine content and 5814 protein-coding sequences. Average nucleotide identity and whole genome phylogenetic analysis delineated the NBAIR BtAr strain as konkukian serovar. Gene ontology analysis revealed associations of 1474, 1323, and 1833 genes with biological processes, molecular function, and cellular components, respectively. Antibiotics & secondary metabolite analysis shell analysis of the whole genome yielded secondary metabolites biosynthetic gene clusters with 100 %, 85 %, 40 %, and 35 % similarity for petrobactin, bacillibactin, fengycin, and paenilamicin, respectively. Also, novel biosynthetic gene clusters, along with antimicrobial genes, including zwittermicin A, chitinase, and phenazines, were identified. Moreover, the presence of eight bacteriophage sequences, 18 genomic islands, insertion sequences, and one CRISPR region indicated prior occurrences of genetic exchange and thus improved competitive fitness of the strain. Overall, the whole genome sequence of NBAIR BtAr is presented, with its taxonomic classification and critical genetic attributes that contribute to its strong antagonistic activity against S. rolfsii.

Enhanced control efficacy of Bacillus subtilis NM4 via integration of chlorothalonil on potato early blight caused by Alternaria solani

Early blight caused by Alternaria solani is a common foliar disease of potato around the world, and serious infections result in reduced yields and marketability due to infected tubers. The major aim of this study is to figure out the synergistic effect between microorganism and fungicides and to evaluate the effectiveness of Bacillus subtilis NM4 in the control of early blight in potato. Based on its colonial morphology and a 16S rRNA analysis, a bacterial antagonist isolated from kimchi was identified as B. subtilis NM4 and it has strong antifungal and anti-oomycete activity against several phytopathogenic fungi and oomycetes. The culture filtrate of strain NM4 with the fungicide effectively suppressed the mycelial growth of A. solani, with the highest growth inhibition rate of 83.48%. Although exposure to culture filtrate prompted hyphal alterations in A. solani, including bulging, combining it with the fungicide caused more severe hyphal damage with continuous bulging. Surfactins and fengycins, two lipopeptide groups, were isolated and identified as the main compounds in two fractions using LC-ESI-MS. Although the surfactin-containing fraction failed to inhibit growth, the fengycin-containing fraction, alone and in combination with chlorothalonil, restricted mycelial development, producing severe hyphal deformations with formation of chlamydospores. A pot experiment combining strain NM4, applied as a broth culture, with fungicide, at half the recommended concentration, resulted in a significant reduction in potato early blight severity. Our results indicate the feasibility of an integrated approach for the management of early blight in potato that can reduce fungicide application rates, promoting a healthy ecosystem in agriculture.

Crude Lipopeptides Produced by Bacillus amyloliquefaciens Could Control the Growth of Alternaria alternata and Production of Alternaria Toxins in Processing Tomato

Alternaria spp. and its toxins are the main contaminants in processing tomato. Based on our earlier research, the current study looked into the anti-fungal capacity of crude lipopeptides from B. amyloliquefaciens XJ-BV2007 against A. alternata. We found that the crude lipopeptides significantly inhibited A. alternata growth and reduced tomato black spot disease incidence. SEM analysis found that the crude lipopeptides could change the morphology of mycelium and spores of A. alternata. Four main Alternaria toxins were detected using UPLC-MS/MS, and the findings demonstrated that the crude lipopeptides could lessen the accumulation of Alternaria toxins in vivo and in vitro. Meanwhile, under the stress of crude lipopeptides, the expression of critical biosynthetic genes responsible for TeA, AOH, and AME was substantially down-regulated. The inhibitory mechanism of the crude lipopeptides was demonstrated to be the disruption of the mycelial structure of A. alternata, as well as the integrity and permeability of the membrane of A. alternata sporocytes. Taken together, crude lipopeptides extracted from B. amyloliquefaciens XJ-BV2007 are an effective biological agent for controlling tomato black spot disease and Alternaria toxins contamination.

Inhibitory effects of Bacillus vallismortis T27 against apple Valsa canker caused by Valsa mali

Apple Valsa canker caused by the pathogenic fungus Valsa mali, are one of the most destructive diseases of woody plants worldwide. One rhizosphere microbe strain, designated as T27 and subsequently identified as Bacillus vallismortis based on morphological and phylogenetic analyses, was studied as a potential biocontrol agent. Inoculation assay showed the B. vallismortis T27 suppressed the mycelial growth of V. mali with 81.33% antifungal effect on dual culture plates and caused hyphal deformities, wrinkles. The T27 fermentation broth significantly suppress the fungi's ability to acidify the surrounding environment. The addition of T27 cell-free supernatant (CFS) caused the pH of the fungal culture medium to increase from 3.60 to 5.10. B. vallismortis T27 showed the presence of Surfactin, IturinA and Bacilysin antimicrobial biosynthetic genes by the PCR assay. In addition, the B. vallismortis T27 was able to promote plant growth by producing siderophores and solubilizing phosphorus. The application of 2% fermentation broth of T27 resulted in a significant increase of 55.99% in the height of tomato plants and a 33.03% increase in the fresh weight of tomatoes. Under laboratory and field conditions, the B. vallismortis T27 exhibited strong antifungal activities on detached twigs and intact plants. The treatment of T27 resulted in a 35.9% reduction in lesion area on detached twigs. Furthermore, when applied to intact plants, T27 demonstrated a scar healing rate of 85.7%, surpassing the 77.8% observed in the treatment with tebuconazole. Comparative transcriptome analysis showed down-regulation of the genes associated with the fungal cell wall and cell membrane's synthesis and composition during V. mali treated with the B. vallismortis T27. In addition, gene transcription level analysis under treatment with B. vallismortis T27 revealed a significant increase in the expression levels of genes associated with diterpene biosynthesis, alanine, aspartic acid and glutamate metabolism, and plant hormone signaling in the apple, consistent with qRT-PCR and RNA-seq results. In this study, B. vallismortis T27 isolated from rhizosphere soil and identified as a novel biological control agent against apple Valsa canker. It exhibited effectively control over Valsa canker through multiple mechanisms, including disrupting the fungal cell membrane structure, altering the fungal growth environment, activating the plant MAPK pathway, and inducing upregulation of plant terpene biosynthetic genes. These findings highlight the potential of B. vallismortis T27 as a promising and multifaceted approach for managing apple Valsa canker.

In vitro assessment of Bacillus subtilis FJ3 affirms its biocontrol and plant growth promoting potential

Bacillus species and their metabolites have potential alternative uses as chemical pesticides that can limit the growth of potential plant pathogens and enhance crop productivity. The aim of this study was to investigate the potential of Bacillus subtilis FJ3 for promoting plant growth and controlling fungal plant pathogens. The study evaluated the ability of the strain to promote plant growth in vitro by characterizing its growth-promoting traits, which included the production of hydrolytic enzymes, indole acetic acid, siderophores, biofilm formation, and phosphate solubilization. Polymerase Chain Reaction (PCR) testing revealed that strain FJ3 has the potential to produce lipopeptides such as fengycin, surfactin, mycosubtilin, and pilpastatin. Through in vitro antagonism testing it was demonstrated that strain FJ3 is able to inhibit Fusarium oxysporum by 52% compared to the untreated control and was antagonistic against Aspergillus flavus, Aspergillus niger, and Rhizopus oryzae using a dual method. The minimum inhibitory concentration of Bacillus crude extract resulted in a 92%, 90%, 81.5%, and 56% growth inhibition of Fusarium oxysporum, A. niger, A. flavus, and Rhizopus oryzae, respectively. In FT-IR and GC-MS analysis of crude LPs extract, the transmission and mass spectrum confirmed the existence of aforesaid lipopeptides containing β-fatty acids with chain lengths ranging from C14 to C21 in which the majority were saturated fatty acids. Greenhouse experimentation revealed that Bacillus strain FJ3 and its metabolites significantly diminished the disease incidence with an average reduction of 31.56%. In sterilized soil, FJ3 and its metabolites caused 24.01% and 10.46% growth promotion, respectively, in chickpea. The results demonstrated that Bacillus strain FJ3 has broad-spectrum antifungal and plant growth-promoting applications and could be a promising candidate for development into a commercialized biobased product for use in sustainable agriculture practice.

Broad-Spectrum Antifungal, Biosurfactants and Bioemulsifier Activity of Bacillus subtilis subsp. spizizenii-A Potential Biocontrol and Bioremediation Agent in Agriculture

In this study, the antifungal, biosurfactant and bioemulsifying activity of the lipopeptides produced by the marine bacterium Bacillus subtilis subsp. spizizenii MC6B-22 is presented. The kinetics showed that at 84 h, the highest yield of lipopeptides (556 mg/mL) with antifungal, biosurfactant, bioemulsifying and hemolytic activity was detected, finding a relationship with the sporulation of the bacteria. Based on the hemolytic activity, bio-guided purification methods were used to obtain the lipopeptide. By TLC, HPLC and MALDI-TOF, the mycosubtilin was identified as the main lipopeptide, and it was further confirmed by NRPS gene clusters prediction based on the strain's genome sequence, in addition to other genes related to antimicrobial activity. The lipopeptide showed a broad-spectrum activity against ten phytopathogens of tropical crops at a minimum inhibitory concentration of 400 to 25 μg/mL and with a fungicidal mode of action. In addition, it exhibited that biosurfactant and bioemulsifying activities remain stable over a wide range of salinity and pH and it can emulsify different hydrophobic substrates. These results demonstrate the potential of the MC6B-22 strain as a biocontrol agent for agriculture and its application in bioremediation and other biotechnological fields.

Microbial Lipopeptides: Properties, Mechanics and Engineering for Novel Lipopeptides

Microorganisms produce active surface agents called lipopeptides (LPs) which are amphiphilic in nature. They are cyclic or linear compounds and are predominantly isolated from Bacillus and Pseudomonas species. LPs show antimicrobial activity towards various plant pathogens and act by inhibiting the growth of these organisms. Several mechanisms are exhibited by LPs, such as cell membrane disruption, biofilm production, induced systematic resistance, improving plant growth, inhibition of spores, etc., making them suitable as biocontrol agents and highly advantageous for industrial utilization. The biosynthesis of lipopeptides involves large multimodular enzymes referred to as non-ribosomal peptide synthases. These enzymes unveil a broad range of engineering approaches through which lipopeptides can be overproduced and new LPs can be generated asserting high efficacy. Such approaches involve several synthetic biology systems and metabolic engineering techniques such as promotor engineering, enhanced precursor availability, condensation domain engineering, and adenylation domain engineering. Finally, this review provides an update of the applications of lipopeptides in various fields.

Harnessing Native Bacillus spp. for Sustainable Wheat Production

The genus Bacillus has been widely applied in contemporary agriculture as an environmentally-friendly biological agent. However, the real effect of commercial Bacillus-based fertilizers and pesticides varies immensely in the field. To harness Bacillus for efficient wheat production, we reviewed the diversity, functionality, and applicability of wheat-associated native Bacillus for the first time. Our main findings are: (i) Bacillus spp. inhabit the rhizosphere, root, stem, leaf, and kernel of wheat; (ii) B. subtilis and B. velezensis are the most widely endophytic species that can be isolated from both below and aboveground tissues; (iii) major functions of these representative strains are promotion of plant growth and alleviation of both abiotic and biotic stresses in wheat; (iv) stability and effectiveness are 2 major challenges during field application; (v) a STVAE pipeline that includes 5 processes, namely, Screen, Test, Validation, Application, and Evaluation, has been proposed for the capture and refinement of wheat-associated Bacillus spp. In particular, this review comprehensively addresses possible solutions, concerns, and criteria during the development of native Bacillus-based inoculants for sustainable wheat production.

Bacillus vallismortis TU-Orga21 blocks rice blast through both direct effect and stimulation of plant defense

Beneficial microorganisms are an important strategy for sustainable plant production processes such as stimulate root exudation, stress tolerance, and yield improvement. This study investigated various microorganisms isolated from the rhizosphere of Oryza sativa L. in order to inhibit Magnaporthe oryzae cause of rice blast, by direct and indirect mode of action. The results indicated that Bacillus vallismortis strain TU-Orga21 significantly reduced M. oryzae mycelium growth and deformed the hyphal structures. The effects of biosurfactant TU-Orga21 was studied against M. oryzae spore development. The dose of ≥5% v/v biosurfactant significantly inhibited the germ tubes and appressoria formation. The biosurfactants were evaluated as surfactin and iturin A by Matrix-assisted laser desorption ionization dual time-of-flight tandem mass spectrometry. Under greenhouse conditions, priming the biosurfactant three times before M. oryzae infection significantly accumulated endogenous salicylic acid, phenolic compounds, and hydrogen peroxide (H₂O₂) during the infection process of M. oryzae. The SR-FT-IR spectral changes from the mesophyll revealed higher integral area groups of lipids, pectins, and proteins amide I and amide II in the elicitation sample. Furthermore, scanning electron microscope revealed appressorium and hyphal enlargement in un-elicitation leaves whereas appressorium formation and hyphal invasion were not found in biosurfactant-elicitation at 24 h post inoculation. The biosurfactant treatment significantly mitigated rice blast disease severity. Therefore, B. vallismortis can be a promising novel biocontrol agent which contains the preformed active metabolites for a rapid control of rice blast by a direct action against pathogen and by boosting plant immunity.

Antagonistic Strain Bacillus halotolerans Jk-25 Mediates the Biocontrol of Wheat Common Root Rot Caused by Bipolaris sorokiniana

Common root rot caused by Bipolaris sorokiniana infestation in wheat is one of the main reasons for yield reduction in wheat crops worldwide. The bacterium strain JK-25 used in the current investigation was isolated from wheat rhizosphere soil and was later identified as Bacillus halotolerans based on its morphological, physiological, biochemical, and molecular properties. The strain showed significant antagonism to B. sorokiniana, Fusarium oxysporum, Fusarium graminearum, and Rhizoctonia zeae. Inhibition of B. sorokiniana mycelial dry weight and spore germination rate by JK-25 fermentation supernatant reached 60% and 88%, respectively. The crude extract of JK-25 was found, by Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), to contain the surfactin that exerted an inhibitory effect on B. sorokiniana. The disruption of mycelial cell membranes was observed under laser scanning confocal microscope (LSCM) after treatment of B. sorokiniana mycelium with the crude extract. The antioxidant enzyme activity of B. sorokiniana was significantly reduced and the oxidation product malondialdehyde (MDA) content increased after treatment with the crude extract. The incidence of root rot was significantly reduced in pot experiments with the addition of JK-25 culture fermentation supernatant, which had a significant biological control effect of 72.06%. Its ability to produce siderophores may help to promote wheat growth and the production of proteases and pectinases may also be part of the strain's role in suppressing pathogens. These results demonstrate the excellent antagonistic effect of JK-25 against B. sorokiniana and suggest that this strain has great potential as a resource for biological control of wheat root rot strains.

Genomic Analysis of Surfactant-Producing Bacillus vallismortis TIM68: First Glimpse at Species Pangenome and Prediction of New Plipastatin-Like Lipopeptide

Surfactants are applied in several industrial processes when the modification of interface activity and the stability of colloidal systems are required. Lipopeptides are a class of microbial biosurfactants produced by species of the Bacillus genus. The present study aimed at assembling and analyzing the genome of a new Bacillus vallismortis strain, TIM68, that was shown to produce surfactant lipopeptides. The draft genome was also screened for common virulence factors and antibiotics resistance genes to investigate the strain biosafety. Comparative genomics analyses, i.e., synteny, average nucleotide identity (ANI), and pangenome, were also carried out using strain TIM68 and publicly available B. vallismortis complete and partial genomes. Three peptide synthetase operons were found in TIM68 genome, and they were surfactin A, mojavensin, and a novel plipastatin-like lipopeptide named vallisin. No virulence factors that render pathogenicity to the strain have been identified, but a region of prophage, that may contain unknown pathogenic factors, has been predicted. The pangenome of the species was characterized as closed, with 57% of genes integrating the core genome. The results obtained here on the genetic potential of TIM68 strain should contribute to its exploration in biotechnological applications.

Biomolecules in modern and sustainable agriculture

This review presents scientific findings which indicate biomolecules are excellent candidates for the development of biopesticides. Efforts are being done to find routes to increase their concentrations in the cultivation media because this concentration facilitates applications, storage, and transportation. Some of these routes are co-fermentation and ultrasound-assisted fermentation. Ultrasonication increases metabolite production and growth rates by improvement of cell permeability and nutrient uptake rates through cell membranes. For example, 24% increase in the enzymatic activity of cellulases produced by Trichoderma reesei in solid-state fermentation was achieved with ultrasonication. Also, chitinase and β-1,3-glucanase productions were stimulated by ultrasound in Beauveria bassiana cultivation, presenting positive results. The common parameters evaluated in the production of biomolecules by ultrasound-assisted fermentation are the duty cycle, time of application, power, energetic density, and how long the sonication is maintained in the fermentation media. Many successful cases are reported and discussed, which include the final formulation of bioproducts for agricultural applications. In this trend, nanotechnology is a promising tool for the development of nanoformulations. Nanoemulsification, green synthesis, biosynthesis, or biogenic synthesis are technologies used to produce such nanoformulations, allowing the controlled release of control agents, as well as the delivery of biomolecules to specific targets.

Reduction of Mycotoxigenic Fungi Growth and Their Mycotoxin Production by Bacillus subtilis QST 713

The use of chemical pesticides to control the occurrence of mycotoxigenic fungi in crops has led to environmental and human health issues, driving the agriculture sector to a more sustainable system. Biocontrol agents such as Bacillus strains and their antimicrobial metabolites have been proposed as alternatives to chemical pesticides. In the present work, a broth obtained from a commercial product containing Bacillus subtilis QST 713 was tested for its ability to inhibit the growth of mycotoxigenic fungi as well as reduce their mycotoxin production. Mass spectrometry analysis of Bacillus subtilis broth allowed to detect the presence of 14 different lipopeptides, belonging to the iturin, fengycin, and surfactin families, already known for their antifungal properties. Bacillus subtilis broth demonstrated to be a useful tool to inhibit the growth of some of the most important mycotoxigenic fungi such as Aspergillus flavus, Fusarium verticillioides, Fusarium graminearum, Aspergillus carbonarius, and Alternaria alternata. In addition, cell-free Bacillus subtilis broth provided the most promising results against the growth of Fusarium graminearum and Alternaria alternata, where the radial growth was reduced up to 86% with respect to the untreated test. With regard to the mycotoxin reduction, raw Bacillus subtilis broth completely inhibited the production of aflatoxin B1, deoxynivalenol, zearalenone, and tenuazonic acid. Cell-free broth provided promising inhibitory properties toward all of the target mycotoxins, even if the results were less promising than the corresponding raw broth. In conclusion, this work showed that a commercial Bacillus subtilis, characterized by the presence of different lipopeptides, was able to reduce the growth of the main mycotoxigenic fungi and inhibit the production of related mycotoxins.

Genomic and Biocontrol Potential of the Crude Lipopeptide by Streptomyces bikiniensis HD-087 Against Magnaporthe oryzae

Rice blast caused by Magnaporthe oryzae is one of the most destructive plant diseases. The secondary metabolites of Streptomyces have potential as biological control agents against M. oryzae. However, no commercial secondary antimicrobial products of Streptomyces have been found by gene prediction, and, particularly relevant for this study, a biocontrol agent obtained from Streptomyces bikiniensis has yet to be found. In this research, genomic analysis was used to predict the secondary metabolites of Streptomyces, and the ability to develop biocontrol pharmaceuticals rapidly was demonstrated. The complete genome of the S. bikiniensis HD-087 strain was sequenced and revealed a number of key functional gene clusters that contribute to the biosynthesis of active secondary metabolites. The crude extract of lipopeptides (CEL) predicted by NRPS gene clusters was extracted from the fermentation liquid of S. bikiniensis HD-087 by acid precipitation followed by methanol extraction, and surfactins, iturins, and fengycins were identified by liquid chromatography-mass spectrometry (LC–MS). In vitro, the CEL of this strain inhibited spore germination and appressorial formation of M. oryzae by destroying membrane integrity and through the leakage of cellular components. In vivo, this CEL reduced the disease index of rice blast by approximately 76.9% on detached leaves, whereas its control effect on leaf blast during pot experiments was approximately 60%. Thus, the S. bikiniensis CEL appears to be a highly suitable alternative to synthetic chemical fungicides for controlling M. oryzae.

Isolation of lipopeptide antibiotics from Bacillus siamensis: A potential biocontrol agent for Fusarium graminearum

Fusarium head blight (FHB), a destructive fungal disease that can cause damage to various crops and reduce yield and quality, is primarily caused by several species of the soil-borne fungal genus Fusarium, which produce mycotoxins that contaminate grain and may cause various severe chronic diseases in humans and livestock. In recent years, Bacillus spp. have been reported as good producer of antifungal antibiotics against FHB. This study aimed to explore the potential role of a newly identified Bacillus strain, designated as CU-XJ-9, against FHB. This strain, which was isolated from traditional Chinese fermented food, was identified as Bacillus siamensis and confirmed to produce lipopeptide biosurfactants, which according to the analysis by quadrupole time-of-flight tandem mass spectrometry (Q-TOF-MS/MS) may belong to the iturin lipopeptide family. The isolated antifungal compounds, at 100 μg/mL, completely inhibited the germination of conidia. Observation of the effects of the isolated antifungal compounds on the mycelia of F. graminearum by scanning electron microscopy revealed obvious nodes in the middle of the mycelia and destroyed mycelial structures, and these changes became more pronounced with increasing dose. Overall, this study provides important information about the ability of Bacillus siamensis to produce lipopeptide biosurfactants, which showed significant antagonistic activity against F. graminearum.

Effects of lipopeptide biosurfactants on clinical strains of Malassezia furfur growth and biofilm formation

Lipopeptide biosurfactants (LBs) are biological molecules with low toxicity that have aroused growing interest in the pharmaceutical industry. Their chemical structure confers antimicrobial and antibiofilm properties against different species. Despite their potential, few studies have demonstrated their capability against Malassezia spp., commensal yeasts which can cause dermatitis and serious infections. Thus, the aim of this study was to evaluate the antifungal activity of biosurfactants produced by new strains of Bacillus subtilis TIM10 and B. vallismortis TIM68 against M. furfur and their potential for removal and inhibition of yeast biofilms. Biosurfactants were classified as lipopeptides by FTIR, and their composition was characterized by ESI-Q-TOF/MS, showing ions for iturin, fengycin, and surfactin, with a greater abundance of surfactin. Through the broth microdilution method, both biosurfactants inhibited the growth of clinical M. furfur strains. Biosurfactant TIM10 showed greater capacity for growth inhibition, with no statistical difference compared to those obtained by the commercial antifungal fluconazole for M. furfur 153DR5 and 154DR8 strains. At minimal inhibitory concentrations (MIC-2), TIM10 and TIM68 were able to inhibit biofilm formation, especially TIM10, with an inhibition rate of approximately 90%. In addition, both biosurfactants were able to remove pre-formed biofilm. Both biosurfactants showed no toxicity against murine fibroblasts, even at concentrations above MIC-2. Our results show the effectiveness of LBs in controlling the growth and biofilm formation of M. furfur clinical strains and highlight the potential of these agents to compose new formulations for the treatment of these fungi.

Identification, characterization and evaluation of novel antifungal cyclic peptides from Neobacillus drentensis

Marine microbes secrete exopolymeric substances (EPS), which surrounds the biofilm and inhibits the fungal growth. Elucidation of the structure and function of the extracellular exopolymeric substances is of vital relevance therapeutically. The active compound responsible for bioactivity was purified and characterized using TLC, LC/MS/MS, GC/MS and FT-IR. Bioactivity of the characterized cyclic peptides (CLPs) against azole resistant and susceptible Candida strains were examined for growth and biofilm formation using scanning electron microscopy, flow cytometry, confocal microscopy. In the present study we identified bioactive cyclic peptides from marine isolated Neobacillus drentensis that exhibited promising tensio-active properties and antifungal efficacy against azole resistant and susceptible Candida albicans. The cluster is composed of five CLP isoforms which were sequenced and identified as new peptides with compositional and structural variations in the amino acid sequence and fatty acid chain. In vitro cytotoxic activity of CLPs was tested in human fibroblast normal cells. We have observed that the CLPs repressed the Candida albicans growth and multiplication by inhibiting the biofilm formation and disruption of branching filamentous hyphae. CLPs have been found to arrest the C. albicans cell cycle by a block at G1-S transition followed by apoptotic cell death. The current studies suggest these natural marine derived CLPs function as potential anti-biofilm agents against azole C. albicans resistant strains.

Genomic and biochemical characterization of antifungal compounds produced by Bacillus subtilis PMB102 against Alternaria brassicicola

Bacillus subtilis is ubiquitous and capable of producing various metabolites, which make the bacterium a good candidate as a biocontrol agent for managing plant diseases. In this study, a phyllosphere bacterium B. subtilis PMB102 isolated from tomato leaf was found to inhibit the growth of Alternaria brassicicola ABA-31 on PDA and suppress Alternaria leaf spot on Chinese cabbage (Brassica rapa). The genome of PMB102 (Accession no. CP047645) was completely sequenced by Nanopore and Illumina technology to generate a circular chromosome of 4,103,088 bp encoding several gene clusters for synthesizing bioactive compounds. PMB102 and the other B. subtilis strains from different sources were compared in pangenome analysis to identify a suite of conserved genes involved in biocontrol and habitat adaptation. Two predicted gene products, surfactin and fengycin, were extracted from PMB102 culture filtrates and verified by LC-MS/MS. The antifungal activity of fengycin was tested on A. brassicicola ABA-31 in bioautography to inhibit hyphae growth, and in co-culturing assays to elicit the formation of swollen hyphae. Our data revealed that B. subtilis PMB102 suppresses Alternaria leaf spot by the production of antifungal metabolites, and fengycin plays an important role to inhibit the vegetative growth of A. brassicicola ABA-31.

Bipolaris sorokiniana-Induced Black Point, Common Root Rot, and Spot Blotch Diseases of Wheat: A Review

Wheat is among the ten top and most widely grown crops in the world. Several diseases cause losses in wheat production in different parts of the world. Bipolaris sorokiniana (teleomorph, Cochliobolus sativus) is one of the wheat pathogens that can attack all wheat parts, including seeds, roots, shoots, and leaves. Black point, root rot, crown rot and spot blotch are the main diseases caused by B. sorokiniana in wheat. Seed infection by B. sorokiniana can result in black point disease, reducing seed quality and seed germination and is considered a main source of inoculum for diseases such as common root rot and spot blotch. Root rot and crown rot diseases, which result from soil-borne or seed-borne inoculum, can result in yield losses in wheat. Spot blotch disease affects wheat in different parts of the world and cause significant losses in grain yield. This review paper summarizes the latest findings on B. sorokiniana, with a specific emphasis on management using genetic, chemical, cultural, and biological control measures.

Isolation and Characterization of Fengycins Produced by Bacillus amyloliquefaciens JFL21 and Its Broad-Spectrum Antimicrobial Potential Against Multidrug-Resistant Foodborne Pathogens

The continuing emergence and development of pathogenic microorganisms that are resistant to antibiotics constitute an increasing global concern, and the effort in new antimicrobials discovery will remain relevant until a lasting solution is found. A new bacterial strain, designated JFL21, was isolated from seafood and identified as B. amyloliquefaciens. The antimicrobial substance produced by B. amyloliquefaciens JFL21 showed low toxicity to most probiotics but exhibited strong antimicrobial activities against multidrug-resistant foodborne pathogens. The partially purified antimicrobial substance, Anti-JFL21, was characterized to be a multiple lipopeptides mixture comprising the families of surfactin, fengycin, and iturin. Compared with commercially available polymyxin B and Nisin, Anti-JFL21 not only could exhibit a wider and stronger antibacterial activity toward Gram-positive pathogens but also inhibit the growth of a majority of fungal pathogens. After further separation through gel filtration chromatography (GFC), the family of surfactin, fengycin, and iturin were obtained, respectively. The results of the antimicrobial test pointed out that only fengycin family presented marked antimicrobial properties against the indicators of L. monocytogenes, A. hydrophila, and C. gloeosporioides, which demonstrated that fengycins might play a major role in the antibacterial and antifungal activity of Anti-JFL21. Additionally, the current study also showed that the fengycins produced by B. amyloliquefaciens JFL21 not only maintained stable anti-Listeria activity over a broad pH and temperature range, but also remained active after treatment with ultraviolet sterilization, chemical reagents, and proteolytic enzymes. Therefore, the results of this study suggest the new strain and its antimicrobials are potentially useful in food preservation for the biological control of the multidrug-resistant foodborne pathogens.

Lesson from Ecotoxicity: Revisiting the Microbial Lipopeptides for the Management of Emerging Diseases for Crop Protection

Microorganisms area treasure in terms of theproduction of various bioactive compounds which are being explored in different arenas of applied sciences. In agriculture, microbes and their bioactive compounds are being utilized in growth promotion and health promotion withnutrient fortification and its acquisition. Exhaustive explorations are unraveling the vast diversity of microbialcompounds with their potential usage in solving multiferous problems incrop production. Lipopeptides are one of such microbial compounds which havestrong antimicrobial properties against different plant pathogens. These compounds are reported to be produced by bacteria, cyanobacteria, fungi, and few other microorganisms; however, genus Bacillus alone produces a majority of diverse lipopeptides. Lipopeptides are low molecular weight compounds which havemultiple industrial roles apart from being usedas biosurfactants and antimicrobials. In plant protection, lipopeptides have wide prospects owing totheirpore-forming ability in pathogens, siderophore activity, biofilm inhibition, and dislodging activity, preventing colonization bypathogens, antiviral activity, etc. Microbes with lipopeptides that haveall these actions are good biocontrol agents. Exploring these antimicrobial compounds could widen the vistasof biological pest control for existing and emerging plant pathogens. The broader diversity and strong antimicrobial behavior of lipopeptides could be a boon for dealing withcomplex pathosystems and controlling diseases of greater economic importance. Understanding which and how these compounds modulate the synthesis and production of defense-related biomolecules in the plants is a key question—the answer of whichneeds in-depth investigation. The present reviewprovides a comprehensive picture of important lipopeptides produced by plant microbiome, their isolation, characterization, mechanisms of disease control, behavior against phytopathogens to understand different aspects of antagonism, and potential prospects for future explorations as antimicrobial agents. Understanding and exploring the antimicrobial lipopeptides from bacteria and fungi could also open upan entire new arena of biopesticides for effective control of devastating plant diseases.

Seed-borne endophytic Bacillus velezensis LHSB1 mediate the biocontrol of peanut stem rot caused by Sclerotium rolfsii

AIMS

This study aimed to obtain an antagonistic endophyte against Sclerotium rolfsii from peanut seeds, evaluate the biocontrol efficacy towards peanut stem rot and explore its antifungal mechanism against S. rolfsii.

METHODS AND RESULTS

Thirty-seven endophytic bacteria were isolated from peanut seeds, six of which exhibited stronger antagonistic activities against S. rolfsii (inhibition rate, IR of hyphae growth ≥70%). Strain LHSB1, the strongest antagonistic strain, was identified as Bacillus velezensis. LHSB1 showed 93·8% of radial growth inhibition of S. rolfsii hyphae and exhibited obvious antagonistic activity against another six pathogenic fungi of peanut. Pot experiments showed two different LHSB1 treatments both significantly reduced the disease incidence and severity of stem rot (P < 0·05) compared to the controls, and the biocontrol efficacy reached 62·6-70·8%, significantly higher than that of Carbendazim control (P < 0·05). Further analyses revealed LHSB1 culture filtrate significantly inhibited sclerotia formation and germination, caused the abnormalities and membrane integrity damage of S. rolfsii hyphae, which might be the possible mode of action of LHSB1 against S. rolfsii. Three antifungal lipopeptides bacillomycin A, surfactin A and fengycin A, were detected in LHSB1 culture extracts by UPLC-ESI-MS, which could be responsible for the biocontrol activity of LHSB1 against S. rolfsii.

CONCLUSION

Our results suggested that the seed-borne endophytic B. velezensis LHSB1 would be a tremendous potential agent for the biocontrol of peanut stem rot caused by S. rolfsii.

SIGNIFICANCE AND IMPACT OF THE STUDY

This comprehensive study provides a candidate endophytic biocontrol strain and reveals its antifungal mechanism against S. rolfsi. To the best of our knowledge, this is the first time that seed-borne endophytic B. velezensis was used as the biocontrol agent to control peanut stem rot.

Fengycin induces ion channels in lipid bilayers mimicking target fungal cell membranes

The one-sided addition of fengycin (FE) to planar lipid bilayers mimicking target fungal cell membranes up to 0.1 to 0.5 μM in the membrane bathing solution leads to the formation of well-defined and well-reproducible single-ion channels of various conductances in the picosiemens range. FE channels were characterized by asymmetric conductance-voltage characteristic. Membranes treated with FE showed nonideal cationic selectivity in potassium chloride bathing solutions. The membrane conductance induced by FE increased with the second power of the lipopeptide aqueous concentration, suggesting that at least FE dimers are involved in the formation of conductive subunits. The pore formation ability of FE was not distinctly affected by the molecular shape of membrane lipids but strongly depended on the presence of negatively charged species in the bilayer. FE channels were characterized by weakly pronounced voltage gating. Small molecules known to modify the transmembrane distribution of electrical potential and the lateral pressure profile were used to modulate the channel-forming activity of FE. The observed effects of membrane modifiers were attributed to changes in lipid packing and lipopeptide oligomerization in the membrane.

Synthesis, Surface and Antimicrobial Activity of New Lactose-Based Surfactants

This work presents a synthesis method for new surfactants based on lactose. The compounds obtained belong to the homologous series of O-β-D-Galactopyranosyl-(1→4)-N-alkyl-(3-sulfopropyl)-D-glucosamine hydrochloride, containing 12 and 14 carbon atoms in the alkyl chain, and they may serve as an example of cationic surfactants. The newly synthesized compounds exhibit good surface properties, low value of CMC (Critical Micelle Concentration) and good wetting properties. These surfactants' ability to produce foam is considerably higher than in the commercial surfactants. Moreover, antibacterial and fungistatic activity was carried out by well diffusion assay against the selected bacteria (Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa), yeasts (Candida albicans) and filamentous fungi (Fusarium graminearum, F. avenaceum, F. oxysporum, F. culmorum, F. equiseti, Alternaria alternata and Botrytis cinerea). It was shown that the resulting quaternary salts significantly inhibit the growth of tested microorganisms. Antibacterial and fungistatic activity of the surfactant compounds varied depending on the species of bacteria or fungi. The results of antimicrobial activity of new lactose derivatives indicate that the compounds exhibit larger or similar antagonistic activity against tested bacteria and fungi than typical cationic surfactant cetylpyridinium chloride.

The Mode of Action of Bacillus Species against Fusarium graminearum, Tools for Investigation, and Future Prospects

Fusarium graminearum is a pervasive plant pathogenic fungal species. Biological control agents employ various strategies to weaken their targets, as shown by Bacillus species, which adopt various mechanisms, including the production of bioactive compounds, to inhibit the growth of F. graminearum. Various efforts to uncover the antagonistic mechanisms of Bacillus against F. graminearum have been undertaken and have yielded a plethora of data available in the current literature. This perspective article attempts to provide a unified record of these interesting findings. The authors provide background knowledge on the use of Bacillus as a biocontrol agent as well as details on techniques and tools for studying the antagonistic mechanism of Bacillus against F. graminearum. Emphasizing its potential as a future biological control agent with extensive use, the authors encourage future studies on Bacillus as a useful antagonist of F. graminearum and other plant pathogens. It is also recommended to take advantage of the newly invented analytical platforms for studying biochemical processes to understand the mechanism of action of Bacillus against plant pathogens in general.

Biocontrol activity of surfactin A purified from Bacillus NH-100 and NH-217 against rice bakanae disease

The potential of the Bacillus genus to antagonize phytopathogens is associated with the production of cyclic lipopeptides. Depending upon the type of lipopeptide, they may serve as biocontrol agents that are eco-friendly alternatives to chemical fertilizers. This study evaluates the biocontrol activity of surfactin-producing Bacillus (SPB) strains NH-100 and NH-217 and purified surfactin A from these strains against rice bakanae disease. Biologically active surfactin fractions were purified by HPLC, and surfactin A variants with chain lengths from C12 to C16 were confirmed by LCMS-ESI. In hemolytic assays, a positive correlation between surfactin A production and halo zone formation was observed. The purified surfactin A had strong antifungal activity against Fusarium oxysporum, F. moniliforme, F. solani, Trichoderma atroviride and T. reesei. Maximum fungal growth suppression (84%) was recorded at 2000 ppm against F. moniliforme. Surfactin A retained antifungal activity at different pH levels (5-9) and temperatures (20, 50 and 121 °C). Hydroponic and pot experiments were conducted to determine the biocontrol activity of SPB strains and the purified surfactin A from these strains on Super Basmati rice. Surfactin production in the rice rhizosphere was detected by LCMS-ESI at early growth stages in hydroponics experiments inoculated with SPB strains. However, the maximum yield was observed with a consortium of SPB strains (T4) and purified surfactin A (T5) treatments in the pot experiment. The outcomes of the present study revealed that surfactin A significantly reduced rice bakanae disease by up to 80%. These findings suggest that purified surfactin A could be an effective biocontrol agent against bakanae disease in rice and should be incorporated into strategies for disease management.

Complete Genome Sequence of Bacillus vallismortis NBIF-001, a Novel Strain from Shangri-La, China, That Has High Activity against Fusarium oxysporum

Bacillus vallismortis NBIF-001, a Gram-positive bacterium, was isolated from soil in Shangri-La, China. Here, we provide the complete genome sequence of this bacterium, which has a 3,929,787-bp-long genome, including 4,030 protein-coding genes and 195 RNA genes. This strain possesses a number of genes encoding virulence factors of pathogens.

Isolation and identification of antifungal peptides from Bacillus amyloliquefaciens W10

Antifungal metabolites produced by Bacillus sp. W10, which was previously isolated from the tomato rhizosphere, were investigated. Strain W10 was identified as Bacillus amyloliquefaciens by analysis of its 16S rDNA and gyrB gene partial sequences. PCR analysis showed the presence of fenB, sfp, and ituD genes, coding for fengycin, surfactin, and iturin, respectively. A novel small antifungal peptide, designated 5240, produced by this strain was isolated by ammonium sulfate precipitation and Superdex 200 gel filtration chromatography. The 5240 peptide was stable at 100 °C for 20 min and remained active throughout a wide pH range (4-10). The antagonistic activity was not affected by protease K and trypsin. The purified 5240 peptide exhibited a broad inhibitory spectrum against various plant pathogenic fungi and was identified as iturin A (C₁₄-C₁₆). Moreover, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry indicated the presence of fengycin A (C₁₄-C₁₅), fengycin B (C₁₆-C₁₇), and surfactin (C₁₃-C₁₆) isoforms in supernatants from strain W10. These results suggest that B. amyloliquefaciens W10 has significant potential as a biocontrol agent.

Evaluation of Bacillus vallismortis (Bacillales: Bacillaceae) R2 as insecticidal agent against polyphagous pest Spodoptera litura (Lepidoptera: Noctuidae)

The insecticidal potential of cells and acid-precipitated biomolecules (APB) of Bacillus vallismortis (Roberts) (Bacillales: Bacillaceae) R2 was evaluated against polyphagous pest Spodoptera litura. The intact cells of isolate R2 and its APB preparation significantly increased larval mortality. Both cells and APB significantly delayed the development and reduced adult emergence of S. litura. The toxicity of isolate R2 was evident from the emergence of morphologically deformed adults with crumpled and underdeveloped wings. The nutritional physiology of larvae fed on APB-supplemented diet was also adversely affected resulting in significant reduction of relative growth and consumption rate as well as efficiency of conversion of ingested and digested food. Thus, the intact viable cells and APB of B. vallismortis R2 may serve as environmental-friendly alternatives to chemical insecticides.