Antifungal Effects of Volatiles Produced by Bacillus subtilis Against Alternaria solani in Potato

Antifungal effects of volatile organic compounds produced by Trichoderma hamatum against Neocosmospora solani

Neocosmospora solani causes Fusarium wilt disease and root rot, which are serious problems worldwide. To determine the growth inhibition of Neocosmospora solani by Trichoderma hamatum volatile organic compounds (VOCs), the major chemical components of Trichoderma hamatum VOCs and the differences in their contents at different times were analysed, and the activity of these components was evaluated. The antifungal activity of Trichoderma hamatum was measured by a screening test, as Trichoderma hamatum exhibited strong antagonism against Neocosmospora solani in vitro. The double plate technique was used to verify the activity of Trichoderma hamatum VOCs, and the inhibition rate was 63.77%. Neocosmospora solani mycelia were uneven and expanded, the contents of the cells leaked, and the mycelia shrank and presented a diaphragm in the hyphae upon Trichoderma hamatum VOCs treatment. Trichoderma hamatum VOCs and their contents at different times were analysed by using gas chromatography-mass spectrometry. 6-Pentyl-2H-pyran-2-one clearly presented in greater amounts than the other components on day 3, 4, 5, and 6. VOCs from Trichoderma hamatum exhibited evident effects on the percentage of healthy fruit after day 3. Moreover, Trichoderma hamatum can improve the biological control of diseases caused by soilborne pathogens, and can be applied in biocontrol fields.

Searching for Chemical Agents Suppressing Substrate Microbiota in White-Rot Fungi Large-Scale Cultivation

Edible fungi are a valuable resource in the search for sustainable solutions to environmental pollution. Their ability to degrade organic pollutants, extract heavy metals, and restore ecological balance has a huge potential for bioremediation. They are also sustainable food resources. Edible fungi (basidiomycetes or fungi from other divisions) represent an underutilized resource in the field of bioremediation. By maximizing their unique capabilities, it is possible to develop innovative approaches for addressing environmental contamination. The aim of the present study was to find selective chemical agents suppressing the growth of microfungi and bacteria, but not suppressing white-rot fungi, in order to perform large-scale cultivation of white-rot fungi in natural unsterile substrates and use it for different purposes. One application could be the preparation of a matrix composed of wooden sleeper (contaminated with PAHs) and soil for further hazardous waste bioremediation using white-rot fungi. In vitro microbiological methods were applied, such as, firstly, compatibility tests between bacteria and white-rot fungi or microfungi, allowing us to evaluate the interaction between different organisms, and secondly, the addition of chemicals on the surface of a Petri dish with a test strain of microorganisms of white-rot fungi, allowing us to determine the impact of chemicals on the growth of organisms. This study shows that white-rot fungi are not compatible to grow with several rhizobacteria or bacteria isolated from soil and bioremediated waste. Therefore, the impact of several inorganic materials, such as lime (hydrated form), charcoal, dolomite powder, ash, gypsum, phosphogypsum, hydrogen peroxide, potassium permanganate, and sodium hydroxide, was evaluated on the growth of microfungi (sixteen strains), white-rot fungi (three strains), and bacteria (nine strains) in vitro. Charcoal, dolomite powder, gypsum, and phosphogypsum did not suppress the growth either of microfungi or of bacteria in the tested substrate, and even acted as promoters of their growth. The effects of the other agents tested were strain dependent. Potassium permanganate could be used for bacteria and Candida spp. growth suppression, but not for other microfungi. Lime showed promising results by suppressing the growth of microfungi and bacteria, but it also suppressed the growth of white-rot fungi. Hydrogen peroxide showed strong suppression of microfungi, and even had a bactericidal effect on some bacteria, but did not have an impact on white-rot fungi. The study highlights the practical utility of using hydrogen peroxide up to 3% as an effective biota-suppressing chemical agent prior to inoculating white-rot fungi in the large-scale bioremediation of polluted substrates, or in the large-scale cultivation for mushroom production as a foodstuff.

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.

Biocontrol and Growth Promotion Potential of Bacillus subtilis CTXW 7-6-2 against Rhizoctonia solani that Causes Tobacco Target Spot Disease

Fungal diseases form perforated disease spots in tobacco plants, resulting in a decline in tobacco yield and quality. The present study investigated the antagonistic effect of Bacillus subtilis CTXW 7-6-2 against Rhizoctonia solani, its ability to promote the growth of tobacco seedlings, and the expression of disease resistance-related genes for efficient and eco-friendly plant disease control. Our results showed that CTXW 7-6-2 had the most vigorous growth after being cultured for 96 h, and its rate of inhibition of R. solani growth in vitro was 94.02%. The volatile compounds produced by CTXW 7-6-2 inhibited the growth of R. solani significantly (by 96.62%). The fungal growthinhibition rate of the B. subtilis CTXW 7-6-2 broth obtained after high-temperature and no-high-temperature sterile fermentation was low, at 50.88% and 54.63%, respectively. The lipopeptides extracted from the B. subtilis CTXW 7-6-2 fermentation broth showed a 74.88% fungal growth inhibition rate at a concentration of 100 mg/l. Scanning and transmission electron microscopy showed some organelle structural abnormalities, collapse, shrinkage, blurring, and dissolution in the R. solani mycelia. In addition, CTXW 7-6-2 increased tobacco seedling growth and improved leaf and root weight compared to the control. After CTXW 7-6-2 inoculation, tobacco leaves showed the upregulation of the PDF1.2, PPO, and PAL genes, which are closely related to target spot disease resistance. In conclusion, B. subtilis CTXW 7-6-2 may be an efficient biological control agent in tobacco agriculture and enhance plant growth potential.

Use of ginger extract and bacterial inoculants for the suppression of Alternaria solani causing early blight disease in Tomato

Early blight (EB), caused by Alternaria solani, is a serious problem in tomato production. Plant growth-promoting rhizobacteria promote plant growth and inhibit plant disease. The present study explored the bio-efficacy of synergistic effect of rhizobacterial isolates and ginger powder extract (GPE) against tomato EB disease, singly and in combination. Six fungal isolates from symptomatic tomato plants were identified as A. solani on the basis of morphological features i.e., horizontal septation (6.96 to 7.93 µm), vertical septation (1.50 to 2.22 µm), conidia length (174.2 to 187.6 µm), conidial width (14.09 to 16.52 µm), beak length (93.06 to 102.26 µm), and sporulation. Five of the twenty-three bacterial isolates recovered from tomato rhizosphere soil were nonpathogenic to tomato seedlings and were compatible with each other and with GPE. Out of five isolates tested individually, three isolates (St-149D, Hyd-13Z, and Gb-T23) showed maximum inhibition (56.3%, 48.3%, and 42.0% respectively) against mycelial growth of A. solani. Among combinations, St-149D + GPE had the highest mycelial growth inhibition (76.9%) over the untreated control. Bacterial strains molecularly characterized as Pseudomonas putida, Bacillus subtilis, and Bacillus cereus and were further tested in pot trials through seed bacterization for disease control. Seeds treated with bacterial consortia + GPE had the highest disease suppression percentage (78.1%), followed by St-149D + GPE (72.2%) and Hyd-13Z + GPE (67.5%). Maximum seed germination was obtained in the bacterial consortia + GPE (95.0 ± 2.04) followed by St-149D + GPE (92.5 ± 1.44) and Hyd-13Z + GPE (90.0 ± 2.04) over control (73.8 ± 2.39) and chemical control as standard treatment (90.0 ± 2). Ginger powder extracts also induce the activation of defence-related enzymes (TPC, PO, PPO, PAL, and CAT) activity in tomato plants. These were highly significant in the testing bacterial inoculants against A. solani infection in tomato crops.

Screening of heavy metal-resistant rhizobial and non-rhizobial microflora isolated from Trifolium sp. growing in mining areas

Plant growth-promoting rhizobacteria (PGPR) can promote plant growth and development with several beneficial effects, especially in challenging environmental conditions, such as the presence of toxic contaminants. In this study, 49 isolates obtained from Trifolium sp. nodules growing on a Pb/Zn mine site were characterized for PGP traits including siderophores production, phosphate solubilization, extracellular enzymes production, and antifungal activity. The isolates were also screened for their ability to grow at increasing concentrations of NaCl and heavy metals, including lead, zinc, cobalt, copper, nickel, cadmium, and chromium. The findings of our study indicated that isolates Cupriavidus paucula RSCup01-RSCup08, Providencia rettgeri RSPro01, Pseudomonas putida RSPs01, Pseudomonas thivervalensis RSPs03-RSPs09, and Acinetobacter beijerinckii RSAci01 showed several key traits crucial for promoting plant growth, thus demonstrating the greatest potential. Most isolates displayed resistance to salt and heavy metals. Notably, Staphylococcus xylosus RSSta01, Pseudomonas sp. RSPs02, Micrococcus yunnanensis RSMicc01, and Kocuria dechangensis RSKoc01 demonstrated a significant capacity to grow at salt concentrations ranging from 10 to 20%, and isolates including Cupravidus paucula RSCup01-RSCup08 exhibited resistance to high levels of heavy metals, up to 1300 mg/L Pb++, 1200 mg/L Zn++, 1000 mg/L Ni++, 1000 mg/L Cd++, 500 mg/L Cu++, 400 mg/L Co++, and 50 mg/L CrVI+. Additionally, the analysis revealed that metal-resistant genes pbrA, czcD, and nccA were exclusively detected in the Cupriavidus paucula RSCup01 strain. The results of this study provide insights into the potential of plant growth-promoting rhizobacteria strains that might be used as inoculants to improve phytoremediation in heavy metal-contaminated soils.

A novel biopolymer technique for encapsulation of Bacillus velezensis BV9 into double coating biopolymer made by in alginate and natural gums to biocontrol of wheat take-all disease

Bacillus velezensis has been known for its high potential in controlling agricultural diseases. Technological advances have opened new perspectives for producing effective formulations by reducing some of the obstacles to their use, such as instability and loss of activity due to exposure to adverse environmental conditions. Encapsulation is one of the new approaches in agricultural science. This research describes discoveries related to processes for the microencapsulation of B. velezensis with natural gums. The efficiency, survival, and controlled release of B. velesensis BV9 encapsulated with alginate mixed with zedo gum, mastic gum, and tragacanth gum were evaluated for this aim. Furthermore, under greenhouse conditions, the encapsulated cells were assessed to control Gaeumannomyces graminis var. tritici in wheat. The results indicated that all tested microcapsules protected >60 % of the bacterial cells. The Alginate-Zedo Gum (Alg-ZG) microcapsules showed a better-controlled release over two months. The greenhouse study indicated that treating wheat plants with Alg-ZG microcapsules was the most efficient treatment, suppressing 100 % of the pathogen. The results indicated that Alg-ZG is the most promising mixture to improve the survivability of B. velezensis BV9. Also, using natural gums and great potential of this formulation provides an effective and affordable fertilizers for agriculture.

Volatile organic compounds produced by Bacillus aryabhattai AYG1023 against Penicillium expansum causing blue mold on the Huangguan pear

Previous research on Bacillus aryabhattai has mainly focused on bioremediation, biosynthesis, and promotion of plant growth, whereas the function of B. aryabhattai on antifungal activity remains to be explored. In this study, we isolated a biocontrol bacterium with antagonistic activity against post-harvest pathogenic fungi by releasing volatile organic compounds (VOCs). We aimed to assess the effectiveness of VOCs produced by B. aryabhattai in prevention of the development of blue mold caused by Penicillium expansum in the Huangguan pear, and reveal the inhibitory mechanism against the pathogenic fungi. Using molecular methods, the biocontrol bacterium was identified as Bacillus aryabhattai AYG1023. 2-Nonanol was identified as the main VOC by solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC/MS). It showed strong inhibition of mycelial growth and conidial germination when treated at the minimum inhibitory concentration (MIC). Scanning and transmission electron microscopy showed that 2-nonanol caused abnormal changes in mycelial and conidial ultrastructure. 2-Nonanol also damaged the integrity of fungal cell membranes and reduced the ergosterol content to 44.77% of P. expansum. In addition, the production of secondary metabolites in P. expansum including patulin and citrinin was significantly reduced by 2-nonanol. Transcriptome analysis revealed that 2-nonanol modulated the expression of genes involved in development, and conidiation pathways, as well as secondary metabolite biosynthesis including steroid biosynthesis, citrinin production and patulin production. Furthermore, blue mold was completely inhibited by treatment with 0.04 μL mL-1 2-nonanol for 48 h on the Huangguan pear. In conclusion, Bacillus aryabhattai AYG1023 was identified as a promising and efficient agent for controlling post-harvest diseases via the release of VOCs, and the outcome of this study lays a theoretical foundation for future applications.

Dimethylpolysulfides production as the major mechanism behind wheat fungal pathogen biocontrol, by Arthrobacter and Microbacterium actinomycetes

IMPORTANCE

As the management of wheat fungal diseases becomes increasingly challenging, the use of bacterial agents with biocontrol potential against the two major wheat phytopathogens, Fusarium graminearum and Zymoseptoria tritici, may prove to be an interesting alternative to conventional pest management. Here, we have shown that dimethylpolysulfide volatiles are ubiquitously and predominantly produced by wheat-associated Microbacterium and Arthrobacter actinomycetes, displaying antifungal activity against both pathogens. By limiting pathogen growth and DON virulence factor production, the use of such DMPS-producing strains as soil biocontrol inoculants could limit the supply of pathogen inocula in soil and plant residues, providing an attractive alternative to dimethyldisulfide fumigant, which has many non-targeted toxicities. Notably, this study demonstrates the importance of bacterial volatile organic compound uptake by inhibited F. graminearum, providing new insights for the study of volatiles-mediated toxicity mechanisms within bacteria-fungus signaling crosstalk.

Biocontrol mechanisms of Bacillus: Improving the efficiency of green agriculture

Species of the genus Bacillus have been widely used for the biocontrol of plant diseases in the demand for sustainable agricultural development. New mechanisms underlying Bacillus biocontrol activity have been revealed with the development of microbiome and microbe-plant interaction research. In this review, we first briefly introduce the typical Bacillus biocontrol mechanisms, such as the production of antimicrobial compounds, competition for niches/nutrients, and induction of systemic resistance. Then, we discussed in detail the new mechanisms of pathogen quorum sensing interference and reshaping of the soil microbiota. The "cry for help" mechanism was also introduced, in which plants can release specific signals under pathogen attack to recruit biocontrol Bacillus for root colonization against invasion. Finally, two emerging strategies for enhancing the biocontrol efficacy of Bacillus agents, including the construction of synthetic microbial consortia and the application of rhizosphere-derived prebiotics, were proposed.

Plant growth-promoting rhizobacteria: a potential bio-asset for restoration of degraded soil and crop productivity with sustainable emerging techniques

The rapid expansion of degraded soil puts pressure on agricultural crop yield while also increasing the likelihood of food scarcity in the near future at the global level. The degraded soil does not suit plants growth owing to the alteration in biogeochemical cycles of nutrients, soil microbial diversity, soil organic matter, and increasing concentration of heavy metals and organic chemicals. Therefore, it is imperative that a solution should be found for such emerging issues in order to establish a sustainable future. In this context, the importance of plant growth-promoting rhizobacteria (PGPR) for their ability to reduce plant stress has been recognized. A direct and indirect mechanism in plant growth promotion is facilitated by PGPR via phytostimulation, biofertilizers, and biocontrol activities. However, plant stress mediated by deteriorated soil at the field level is not entirely addressed by the implementation of PGPR at the field level. Thus, emerging methods such as CRISPR and nanotechnological approaches along with PGPR could manage degraded soil effectively. In the pursuit of the critical gaps in this respect, the present review discusses the recent advancement in PGPR action when used along with nanomaterials and CRISPR, impacting plant growth under degraded soil, thereby opening a new horizon for researchers in this field to mitigate the challenges of degraded soil.

Unveiling the Potential of Bacillus safensis Y246 for Enhanced Suppression of Rhizoctonia solani

Rhizoctonia solani is a significant pathogen affecting various crops, including tobacco. In this study, a bacterial strain, namely Y246, was isolated from the soil of healthy plants and exhibited high antifungal activity. Based on morphological identification and DNA sequencing, this bacterial strain was identified as Bacillus safensis. The aim of this investigation was to explore the antifungal potential of strain Y246, to test the antifungal stability of Y246 by adjusting different cultivation conditions, and to utilize gas chromatography-mass spectrometry (GC-MS) to predict the volatile compounds related to antifungal activity in Y246. In vitro assays demonstrated that strain Y246 exhibited a high fungal inhibition rate of 76.3%. The fermentation broth and suspension of strain Y246 inhibited the mycelial growth of R. solani by 66.59% and 63.75%, respectively. Interestingly, treatment with volatile compounds derived from the fermentation broth of strain Y246 resulted in abnormal mycelial growth of R. solani. Scanning electron microscopy analysis revealed bent and deformed mycelium structures with a rough surface. Furthermore, the stability of antifungal activity of the fermentation broth of strain Y246 was assessed. Changes in temperature, pH value, and UV irradiation time had minimal impact on the antifungal activity, indicating the stability of the antifungal activity of strain Y246. A GC-MS analysis of the volatile organic compounds (VOCs) produced by strain Y246 identified a total of 34 compounds with inhibitory effects against different fungi. Notably, the strain demonstrated broad-spectrum activity, exhibiting varying degrees of inhibition against seven pathogens (Alternaria alternata, Phomopsis. sp., Gloeosporium musarum, Dwiroopa punicae, Colletotrichum karstii, Botryosphaeria auasmontanum, and Botrytis cinerea). In our extensive experiments, strain Y246 not only exhibited strong inhibition against R. solani but also demonstrated remarkable inhibitory effects on A. alternata-induced tobacco brown spot and kiwifruit black spot, with impressive inhibition rates of 62.96% and 46.23%, respectively. Overall, these findings highlight the significant antifungal activity of B. safensis Y246 against R. solani. In addition, Y246 has an excellent antifungal stability, with an inhibition rate > 30% under different treatments (temperature, pH, UV). The results showed that the VOCs of strain Y246 had a strong inhibitory effect on the colony growth of R. solani, and the volatile substances produced by strain Y246 had an inhibitory effect on R. solani at rate of 70.19%. Based on these results, we can conclude that Y246 inhibits the normal growth of R. solani. These findings can provide valuable insights for developing sustainable agricultural strategies.

Genome sequencing and analysis of Bacillus velezensis VJH504 reveal biocontrol mechanism against cucumber Fusarium wilt

One major issue in reducing cucumber yield is the destructive disease Cucumber (Cucumis sativus L.) wilt disease caused by Fusarium oxysporum f. sp. cucumerinum (Foc). When using the isolate VJH504 isolated from cucumber rhizosphere soil and identified as Bacillus velezensis, the growth of Foc in the double culture experiment was effectively inhibited. Phenotypic, phylogenetic, and genomic analyses were conducted to enhance understanding of its biocontrol mechanism. According to the result of the phenotype analysis, B. velezensis VJH504 could inhibit cucumber fusarium wilt disease both in vitro and in vivo, and significantly promote cucumber seed germination and seedling growth. Additionally, the tests of growth-promoting and biocontrol characteristics revealed the secretion of proteases, amylases, β-1,3-glucanases, cellulases, as well as siderophores and indole-3-acetic acid by B. velezensis VJH504. Using the PacBio Sequel II system, we applied the complete genome sequencing for B. velezensis VJH504 and obtained a single circular chromosome with a size of 3.79 Mb. A phylogenetic tree was constructed based on the 16S rRNA gene sequences of B. velezensis VJH504 and 13 other Bacillus species, and Average Nucleotide Identity (ANI) analysis was performed using their whole-genome sequences, confirming isolateVJH504 as B. velezensis. Following this, based on the complete genome sequence od B. velezensis VJH504, specific functional analysis, Carbohydrate-Active Enzymes (CAZymes) analysis, and secondary metabolite analysis were carried out, predicting organism's abilities for biofilm formation, production of antifungal CAZymes, and synthesis of antagonistic secondary metabolites against pathogens. Afterwards, a comparative genomic analysis was performed between B. velezensis VJH504 and three other B. velezensis strains, revealing subtle differences in their genomic sequences and suggesting the potential for the discovery of novel antimicrobial substances in B. velezensis VJH504. In conclusion, the mechanism of B. velezensis VJH504 in controlling cucumber fusarium wilt was predicted to appear that B. velezensis VJH504is a promising biocontrol agent, showcasing excellent application potential in agricultural production.

Use of Trichoderma culture filtrates as a sustainable approach to mitigate early blight disease of tomato and their influence on plant biomarkers and antioxidants production

Introduction

Alternaria solani is a challenging pathogen in the tomato crop globally. Chemical control is a rapid approach, but emerging fungicide resistance has become a severe threat. The present study investigates the use of culture filtrates (CFs) of three species of Trichoderma spp. to control this disease.

Methods

Highly virulent A. solani strain and three Trichoderma fungal strains viz., T. harzianum (Accession No: MW590687), T. atroviride (Accession No: MW590689) and T. longibrachiatum (Accession No: MW590688) previously isolated by authors were used in this study. The efficacy of culture filtrates (CFs) to mitigate early blight disease were tested under greenhouse and field conditions, experiments were conducted in different seasons of 2020 using a tomato variety "doucen".

Results and discussion

The CFs of T. harzianum, T. longibrachiatum, and T. atroviride significantly inhibited the in vitro mycelial growth of A. solani (62.5%, 48.73%, and 57.82%, respectively, followed by control 100%). In the GC-MS analysis of Trichoderma CF volatile compounds viz., harzianic acid (61.86%) in T. harzianum, linoleic acid (70.02%) in T. atroviride, and hydroxymethylfurfural (68.08%) in the CFs of T. longibrachiatum, were abundantly present. Foliar application of CFs in the greenhouse considerably reduced the disease severity (%) in all treatments, viz., T. harzianum (18.03%), T. longibrachiatum (31.91%), and T. atroviride (23.33%), followed by infected control (86.91%), and positively affected the plant biomarkers. In the greenhouse, the plants treated with CFs demonstrated higher flavonoids after 6 days of inoculation, whereas phenolic compounds increased after 2 days. The CF-treated plants demonstrated higher antioxidant enzymes, i.e., phenylalanine ammonia-lyase (PAL) and peroxidase (POD), after 4 days, whereas polyphenol oxidase (PPO) was higher after 6 days of inoculation, followed by healthy and infected controls. In open field conditions, disease severity in CF-treated plants was reduced in both seasons as compared to naturally infected plants, whereas CF-treated plants exhibited a higher fruit yield than controls. The present results conclude that CFs can be a potential biocontrol candidate and a promising alternative to the early blight pathogen for sustainable production.

Tissue Extract from Brittle Star Undergoing Arm Regeneration Promotes Wound Healing in Rat

This study set out to evaluate the wound healing properties of brittle star extracts in vitro and in vivo. Due to the great arm regeneration potential of the brittle star, Ophiocoma cynthiae, the present study aimed to evaluate the wound healing effect of hydroalcoholic extracts of brittle star undergoing arm regeneration in wound healing models. The brittle star samples were collected from Nayband Bay, Bushehr, Iran. After wound induction in the arm of brittle stars, hydroalcoholic extracts relating to different times of arm regeneration were prepared. The GC-MS analysis, in vitro MTT cell viability and cell migration, Western blot, and computational analysis tests were performed. Based on the in vitro findings, two BSEs were chosen for in vivo testing. Macroscopic, histopathological and biochemical evaluations were performed after treatments. The results showed positive proliferative effects of BSEs. Specifically, forty-two compounds were detected in all groups of BSEs using GC-MS analysis, and their biological activities were assessed. The MTT assay showed that the 14 d BSE had a higher proliferative effect on HFF cells than 7 d BSE. The cell migration assay showed that the wound area in 7 d and 14 d BSEs was significantly lower than in the control group. Western blot analysis demonstrated an increase in the expression of proliferation-related proteins. Upon the computational analysis, a strong affinity of some compounds with proteins was observed. The in vivo analysis showed that the evaluation of wound changes and the percentage of wound healing in cell migration assay in the 7 d BSE group was better than in the other groups. Histopathological scores of the 7 d BSE and 14 d BSE groups were significantly higher than in the other groups. In conclusion, the hydroalcoholic extract of O. cynthiae undergoing arm regeneration after 7 and 14 days promoted the wound healing process in the cell and rat skin wound healing model due to their proliferative and migratory biological activity.

Bacillus velezensis Strain HN-Q-8 Induced Resistance to Alternaria solani and Stimulated Growth of Potato Plant

Bacillus velezensis HN-Q-8, isolated in our previous study, has an antagonistic effect on Alternaria solani. After being pretreated with a fermentation liquid with HN-Q-8 bacterial cell suspensions, the potato leaves inoculated with A. solani displayed smaller lesion areas and less yellowing than the controls. Interestingly, the activity levels of superoxide dismutase, peroxidase, and catalase in potato seedlings were enhanced by the addition of the fermentation liquid with bacterial cells. Additionally, the overexpression of key genes related to induced resistance in the Jasmonate/Ethylene pathway was activated by the addition of the fermentation liquid, suggesting that the HN-Q-8 strain induced resistance to potato early blight. In addition, our laboratory and field experiments showed that the HN-Q-8 strain can promote potato seedling growth and significantly increase tuber yield. The root activity and chlorophyll content of potato seedlings were significantly increased along with the levels of indole acetic acid, gibberellic acid 3, and abscisic acid upon addition of the HN-Q-8 strain. The fermentation liquid with bacterial cells was more efficient in inducing disease resistance and promoting growth than bacterial cell suspensions alone or the fermentation liquid without bacterial cells. Thus, the B. velezensis HN-Q-8 strain is an effective bacterial biocontrol agent, augmenting the options available for potato cultivation.

Suppressive Effects of Volatile Compounds from Bacillus spp. on Magnaporthe oryzae Triticum (MoT) Pathotype, Causal Agent of Wheat Blast

The Magnaporthe oryzae Triticum (MoT) pathotype is the causal agent of wheat blast, which has caused significant economic losses and threatens wheat production in South America, Asia, and Africa. Three bacterial strains from rice and wheat seeds (B. subtilis BTS-3, B. velezensis BTS-4, and B. velezensis BTLK6A) were used to explore the antifungal effects of volatile organic compounds (VOCs) of Bacillus spp. as a potential biocontrol mechanism against MoT. All bacterial treatments significantly inhibited both the mycelial growth and sporulation of MoT in vitro. We found that this inhibition was caused by Bacillus VOCs in a dose-dependent manner. In addition, biocontrol assays using detached wheat leaves infected with MoT showed reduced leaf lesions and sporulation compared to the untreated control. VOCs from B. velezensis BTS-4 alone or a consortium (mixture of B. subtilis BTS-3, B. velezensis BTS-4, and B. velezensis BTLK6A) of treatments consistently suppressed MoT in vitro and in vivo. Compared to the untreated control, VOCs from BTS-4 and the Bacillus consortium reduced MoT lesions in vivo by 85% and 81.25%, respectively. A total of thirty-nine VOCs (from nine different VOC groups) from four Bacillus treatments were identified by gas chromatography-mass spectrometry (GC-MS), of which 11 were produced in all Bacillus treatments. Alcohols, fatty acids, ketones, aldehydes, and S-containing compounds were detected in all four bacterial treatments. In vitro assays using pure VOCs revealed that hexanoic acid, 2-methylbutanoic acid, and phenylethyl alcohol are potential VOCs emitted by Bacillus spp. that are suppressive for MoT. The minimum inhibitory concentrations for MoT sporulation were 250 mM for phenylethyl alcohol and 500 mM for 2-methylbutanoic acid and hexanoic acid. Therefore, our results indicate that VOCs from Bacillus spp. are effective compounds to suppress the growth and sporulation of MoT. Understanding the MoT sporulation reduction mechanisms exerted by Bacillus VOCs may provide novel options to manage the further spread of wheat blast by spores.

Isolation and Genome-Based Characterization of Biocontrol Potential of Bacillus siamensis YB-1631 against Wheat Crown Rot Caused by Fusarium pseudograminearum

Fusarium crown rot (FCR) caused by Fusarium pseudograminearum is one of the most serious soil-borne diseases of wheat. Among 58 bacterial isolates from the rhizosphere soil of winter wheat seedlings, strain YB-1631 was found to have the highest in vitro antagonism to F. pseudograminearum growth. LB cell-free culture filtrates inhibited mycelial growth and conidia germination of F. pseudograminearum by 84.14% and 92.23%, respectively. The culture filtrate caused distortion and disruption of the cells. Using a face-to-face plate assay, volatile substances produced by YB-1631 inhibited F. pseudograminearum growth by 68.16%. In the greenhouse, YB-1631 reduced the incidence of FCR on wheat seedlings by 84.02% and increased root and shoot fresh weights by 20.94% and 9.63%, respectively. YB-1631 was identified as Bacillus siamensis based on the gyrB sequence and average nucleotide identity of the complete genome. The complete genome was 4,090,312 bp with 4357 genes and 45.92% GC content. In the genome, genes were identified for root colonization, including those for chemotaxis and biofilm production, genes for plant growth promotion, including those for phytohormones and nutrient assimilation, and genes for biocontrol activity, including those for siderophores, extracellular hydrolase, volatiles, nonribosomal peptides, polyketide antibiotics, and elicitors of induced systemic resistance. In vitro production of siderophore, β-1, 3-glucanase, amylase, protease, cellulase, phosphorus solubilization, and indole acetic acid were detected. Bacillus siamensis YB-1631 appears to have significant potential in promoting wheat growth and controlling wheat FCR caused by F. pseudograminearum.

Bacillus VOCs in the Context of Biological Control

A contemporary agricultural production system relying on heavy usage of agrochemicals represents a questionable outlook for sustainable food supply in the future. The visible negative environmental impacts and unforeseen consequences to human and animal health have been requiring a shift towards the novel eco-friendly alternatives for chemical pesticides for a while now. Microbial-based biocontrol agents have shown a promising potential for plant disease management. The bacteria of the genus Bacillus have been among the most exploited microbial active components due to several highly efficient mechanisms of action against plant pathogens, as well as a palette of additional plant-beneficial mechanisms, together with their suitable properties for microbial biopesticide formulations. Among other bioactive metabolites, volatile organic compounds (VOCs) have been investigated for their biocontrol applications, exhibiting the main advantage of long-distance effect without the necessity for direct contact with plants or pathogens. The aim of this study is to give an overview of the state-of-the-art in the field of Bacillus-based VOCs, especially in terms of their antibacterial, antifungal, and nematicidal action as the main segments determining their potential for biocontrol applications in sustainable agriculture.

Classification and Multifaceted Potential of Secondary Metabolites Produced by Bacillus subtilis Group: A Comprehensive Review

Despite their remarkable biosynthetic potential, Bacillus subtilis have been widely overlooked. However, their capability to withstand harsh conditions (extreme temperature, Ultraviolet (UV) and γ-radiation, and dehydration) and the promiscuous metabolites they synthesize have created increased commercial interest in them as a therapeutic agent, a food preservative, and a plant-pathogen control agent. Nevertheless, the commercial-scale availability of these metabolites is constrained due to challenges in their accessibility via synthesis and low fermentation yields. In the context of this rising in interest, we comprehensively visualized the antimicrobial peptides produced by B. subtilis and highlighted their prospective applications in various industries. Moreover, we proposed and classified these metabolites produced by the B. subtilis group based on their biosynthetic pathways and chemical structures. The biosynthetic pathway, bioactivity, and chemical structure are discussed in detail for each class. We believe that this review will spark a renewed interest in the often disregarded B. subtilis and its remarkable biosynthetic capabilities.

Biocontrol and plant growth promotion potential of endophytic Bacillus subtilis JY-7-2L on Aconitum carmichaelii Debx

Aconitum carmichaelii Debx. is a famous medicinal plant rich in alkaloids and widely used to treat various human diseases in Asian countries. However, southern blight caused by Sclerotium rolfsii severely hampered the yield of A. carmichaelii. Beneficial microbe-based biological control is becoming a promising alternative and an environmentally friendly approach for the management of plant diseases. In this study, we evaluated the biocontrol potential of an endophytic bacterial strain JY-7-2L, which was isolated from the leaves of A. carmichaelii, against southern blight in vitro and by a series of field experiments. JY-7-2L was identified as Bacillus subtilis based on multi-locus sequence analysis. JY-7-2L showed strong antagonistic activity against S. rolfsii in vitro and on A. carmichaelii root slices by dual-culture assay. Cell-free culture filtrate of JY-7-2L significantly inhibited the hyphal growth, sclerotia formation, and germination of S. rolfsii. In addition, volatile compounds produced by JY-7-2L completely and directly inhibited the growth of S. rolfsii. Furthermore, JY-7-2L was proved to produce hydrolytic enzymes including glucanase, cellulase, protease, indole acetic acid, and siderophore. The presence of bacA, fenA, fenB, fenD, srfAA, and baeA genes by PCR amplification indicated that JY-7-2L was able to produce antifungal lipopeptides and polyketides. Field trials indicated that application of the JY-7-2L fermentation culture significantly reduced southern blight disease severity by up to 30% with a long-acting duration of up to 62 days. Meanwhile, JY-7-2L significantly promoted the fresh and dry weights of the stem, main root, and lateral roots of A. carmichaelii compared to non-inoculation and/or commercial B. subtilis product treatments. Taken together, JY-7-2L can be used as a promising biocontrol agent for the control of southern blight in A. carmichaelii.

Identification and functional analysis of protein secreted by Alternaria solani

Early blight, caused by the necrotrophic fungus Alternaria solani, is an important foliar disease that causes major yield losses of potato. Effector proteins secreted by pathogens to host cells can inhibit host immune response to pathogens. Currently, the function of effector proteins secreted by A. solani during infection is poorly understood. In this study, we identified and characterized a novel candidate effector protein, AsCEP50. AsCEP50 is a secreted protein that is highly expressed throughout the infection stages of A. solani. Agrobacterium tumefaciens-mediated transient expression in Nicotiana benthamiana and tomato demonstrated that AsCEP50 is located on the plasma membrane of N. benthamiana and regulates senescence-related genes, resulting in the chlorosis of N. benthamiana and tomato leaves. Δ50 mutants were unaffected in vegetative growth, spore formation and mycelium morphology. However, the deletion of AsCEP50 significantly reduced virulence, melanin production and penetration of A. solani. These results strongly supported that AsCEP50 is an important pathogenic factor at the infection stage and contributes to the virulence of Alternaria solani.

Fusel oil reaction in pressurized water: characterization and antimicrobial activity

This work aimed to investigate the reaction of fusel oil (FO) with pressurized water in a continuous flow reactor, in order to verify the effect of operating conditions (temperature and alcohol to water ratio) on the formation of reaction products, as well as to potentiate the antimicrobial activity of FO. The characterization of the FO was performed by high resolution mass spectrometry (ESI-TOF) and by a chromatograph coupled to mass spectrometry (GC-MS), and the reaction products were characterized by ESI-TOF and evaluated for antifungal potential. From the results, it was verified that the FO contained 70.58 wt% of isoamyl alcohol and was formed mainly by the organic functions alcohols, aldehydes, ketones and lipids. The reaction mechanisms that prevailed during the reactions conducted in subcritical and supercritical states were dehydration and reduction, respectively, making it possible to identify pyrazine derivatives compounds in the reaction products. The fungus Irpex lacteus showed greater resistance under the application of reaction products, and the products obtained at 300 °C and 400 °C showed an inhibition percentage of 96.07% to Schizophyllum commune and 96.50% to Trametes versicolor, respectively.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03429-3.

Comprehensive review on patulin and Alternaria toxins in fruit and derived products

Mycotoxins are toxic secondary metabolites produced by certain fungi, which can contaminate various food commodities, including fruits and their derived products. Patulin and Alternaria toxins are among the most commonly encountered mycotoxins in fruit and their derived products. In this review, the sources, toxicity, and regulations related to these mycotoxins, as well as their detection and mitigation strategies are widely discussed. Patulin is a mycotoxin produced mainly by the fungal genera Penicillium, Aspergillus, and Byssochlamys. Alternaria toxins, produced by fungi in the Alternaria genus, are another common group of mycotoxins found in fruits and fruit products. The most prevalent Alternaria toxins are alternariol (AOH) and alternariol monomethyl ether (AME). These mycotoxins are of concern due to their potential negative effects on human health. Ingesting fruits contaminated with these mycotoxins can cause acute and chronic health problems. Detection of patulin and Alternaria toxins in fruit and their derived products can be challenging due to their low concentrations and the complexity of the food matrices. Common analytical methods, good agricultural practices, and contamination monitoring of these mycotoxins are important for safe consumption of fruits and derived products. And Future research will continue to explore new methods for detecting and managing these mycotoxins, with the ultimate goal of ensuring the safety and quality of fruits and derived product supply.

Two Metalloproteases VdM35-1 and VdASPF2 from Verticillium dahliae Are Required for Fungal Pathogenicity, Stress Adaptation, and Activating Immune Response of Host

Verticillium dahliae is a soilborne fungus that causes destructive vascular wilt diseases in a wide range of plant hosts. In this study, we identified two M35 family metalloproteinases: VdM35-1 and VdASPF2, and investigated their function in vitro and in vivo. The results showed that VdM35-1 and VdASPF2 were located in the cell membrane, as secreted proteins depended on signal peptide, and two histidine residues (H) induced cell death and activated plant immune response. VdM35-1 depended on membrane receptor proteins NbBAK1 and NbSOBIR1 in the process of inducing cell death, while VdASPF2 did not depend on them. The deletion of VdM35-1 and VdASPF2 led to the decrease of sporulation and the slow shortening of mycelial branch growth, and the spore morphology of VdM35-1-deficient strain became malformed. In addition, ΔVdM35-1 and ΔVdASPF2 showed more sensitive to osmotic stress, SDS, Congo red (CR), and high temperature. In terms of the utilization of carbon sources, the knockout mutants exhibited decreased utilization of carbon sources, and the growth rates on the medium containing sucrose, starch, and pectin were lower than the wild type strain, with significantly limited growth, especially on galactose-containing medium. Furthermore, ΔVdM35-1 and ΔVdASPF2 showed a significant reduction in pathogenicity. Collectively, these results suggested that VdM35-1 and VdASPF2 were important multifunction factors in the pathogenicity of V. dahliae and relative to stress adaptation and activated plant immune response. IMPORTANCE Verticillium wilt, caused by the notorious fungal pathogen V. dahliae, is one of the main limiting factors for agricultural production. Metalloproteases played an important role in the pathogenic mechanism of pathogens. Our research found that M35 family metalloproteases VdM35-1 and VdASPF2 played an important role in the development, adaptability, and pathogenicity of V. dahliae, providing a new perspective for further understanding the molecular mechanism of virulence of fungal pathogens.

Identification of effector CEP112 that promotes the infection of necrotrophic Alternaria solani

BACKGROUND

Alternaria solani is a typical necrotrophic pathogen that can cause severe early blight on Solanaceae crops and cause ring disease on plant leaves. Phytopathogens produce secretory effectors that regulate the host immune response and promote pathogenic infection. Effector proteins, as specialized secretions of host-infecting pathogens, play important roles in disrupting host defense systems. At present, the role of the effector secreted by A. solani during infection remains unclear. We report the identification and characterization of AsCEP112, an effector required for A. solani virulence.

RESULT

The AsCEP112 gene was screened from the transcriptome and genome of A. solani on the basis of typical effector signatures. Fluorescence quantification and transient expression analysis showed that the expression level of AsCEP112 continued to increase during infection. The protein localized to the cell membrane of Nicotiana benthamiana and regulated senescence-related genes, resulting in the chlorosis of N. benthamiana and tomato leaves. Moreover, comparative analysis of AsCEP112 mutant obtained by homologous recombination with wild-type and revertant strains indicated that AsCEP112 gene played an active role in regulating melanin formation and penetration in the pathogen. Deletion of AsCEP112 also reduced the pathogenicity of HWC-168.

CONCLUSION

Our findings demonstrate that AsCEP112 was an important effector protein that targeted host cell membranes. AsCEP112 regulateed host senescence-related genes to control host leaf senescence and chlorosis, and contribute to pathogen virulence.

Dormancy and germination of microsclerotia of Verticillium longisporum are regulated by soil bacteria and soil moisture levels but not by nutrients

The soil-borne pathogen Verticillium longisporum infects roots of its host plant, oilseed rape, and systemically colonizes stems where it finally forms microsclerotia at crop maturity. Once returned to the soil after harvest, microsclerotia undergo a stage of dormancy, in which they may survive for several years. Since there is neither efficient chemical control nor effective resistance in oilseed rape cultivars to control the disease, alternative control strategies may consist in regulating the germination and dormancy of microsclerotia in the soil. Therefore, a series of experiments were conducted to explore the effects of nutrients, soil moisture, and the soil microbiome on germination of dormant microsclerotia. Experiments with microsclerotia exposed in vitro to different nutrients indicated that under sterile conditions the stimulating effect of nutrients on microsclerotia germination was not enhanced as compared to water. Moreover, further assays revealed a strong inhibitory effect of unsterile soil on microsclerotia germination. Accordingly, oilseed rape plants inoculated with microsclerotia of V. longisporum showed severe infection with V. longisporum when grown in autoclaved soil, in contrast to plants grown in unsterile soil. These experiments indicate a crucial role of soil fungistasis and thus the soil microbiome on microsclerotia germination. Further bioassays demonstrated that viable soil bacteria obtained from the rhizosphere of oilseed rape plants and bulk field soil effectively inhibited microsclerotia germination, whereas dead bacteria and bacterial culture filtrates hardly suppressed germination. A putative inhibitory role of volatile organic compounds (VOCs) produced by soil bacteria was confirmed in two-compartment Petri dishes, where microsclerotia germination and colony growth were significantly inhibited. Bacterial VOCs were collected and analyzed by GC–MS. In total, 45 VOCs were identified, among which two acid and two alcohol compounds were emitted by all tested bacteria. A bioassay, conducted with corresponding pure chemicals in two-compartment Petri dishes, indicated that all acidic volatile compounds, including 3-methylbutanoic acid, 2-methylbutanoic acid, hexanoic acid, and 2-methylpropionic acid, induced strong inhibitory effects on microsclerotia. We conclude that bacterial acidic volatiles play a key role in the fungistatic effect on microsclerotia of V. longisporum in the soil and could thus be targeted for development of novel strategies to control this pathogen by artificially regulating dormancy of microsclerotia in soil.

Metabolites derived from fungi and bacteria suppress in vitro growth of Gnomoniopsis smithogilvyi, a major threat to the global chestnut industry

INTRODUCTION

Chestnut rot caused by the fungus Gnomoniopsis smithogilvyi is a disease present in the world's major chestnut growing regions. The disease is considered a significant threat to the global production of nuts from the sweet chestnut (Castanea sativa). Conventional fungicides provide some control, but little is known about the potential of biological control agents (BCAs) as alternatives to manage the disease.

OBJECTIVE

Evaluate whether formulated BCAs and their secreted metabolites inhibit the in vitro growth of G. smithogilvyi.

METHODS

The antifungal potential of BCAs was assessed against the pathogen through an inverted plate assay for volatile compounds (VOCs), a diffusion assay for non-volatile compounds (nVOCs) and in dual culture. Methanolic extracts of nVOCs from the solid medium were further evaluated for their effect on conidia germination and were screened through an LC-MS-based approach for antifungal metabolites.

RESULTS

Isolates of Trichoderma spp., derived from the BCAs, significantly suppressed the pathogen through the production of VOCs and nVOCs. The BCA from which Bacillus subtilis was isolated was more effective in growth inhibition through the production of nVOCs. The LC-MS based metabolomics on the nVOCs derived from the BCAs showed the presence of several antifungal compounds.

CONCLUSION

The results show that G. smithogilvyi can be effectively controlled by the BCAs tested and that their use may provide a more ecological alternative for managing chestnut rot. The in vitro analysis should now be expanded to the field to assess the effectiveness of these alternatives for chestnut rot management.

Effects of Volatile Organic Compounds Produced by Pseudomonas aurantiaca ST-TJ4 against Verticillium dahliae

Verticillium dahliae is one of the most destructive fungal pathogens, causing substantial economic losses in agriculture and forestry. The use of plant growth-promoting rhizobacteria (PGPR) is an effective and environmentally friendly strategy for controlling diseases caused by V. dahliae. In this study, 90 mm in diameter Petri plates were used to test the effect of volatile organic compounds (VOCs) produced by different concentrations of Pseudomonasaurantiaca ST-TJ4 cells suspension on V. dahliae mycelia radial growth and biomass. The mycelial morphology was observed by using scanning electron microscopy. The conidia germination and microsclerotia formation of V. dahliae were evaluated. The VOCs with antifungal activity were collected by headspace solid-phase microextraction (SPME), and their components were analyzed by gas chromatography-mass spectrometry (GC-MS). The VOCs produced by strain ST-TJ4 significantly inhibited the growth of mycelium of V. dahliae. The morphology of the hyphae was rough and wrinkled when exposed to VOCs. The VOCs of strain ST-TJ4 have a significant inhibitory effect on V. dahliae conidia germination and microsclerotia formation. At the same time, the VOCs also reduce the expression of genes related to melanin synthesis in V. dahliae. In particular, the expression of the hydrophobin gene (VDAG-02273) was down-regulated the most, about 67-fold. The VOCs effectively alleviate the severity of cotton root disease. In the volatile profile of strain ST-TJ4, 2-undecanone and 1-nonanol assayed in the range 10–200 µL per plate revealed a significant inhibitory effect on V. dahliae mycelial radial growth. These compounds may be useful to devise new control strategies for control of Verticillium wilt disease caused by V. dahliae.

Biocontrol and Action Mechanism of Bacillus subtilis Lipopeptides' Fengycins Against Alternaria solani in Potato as Assessed by a Transcriptome Analysis

Alternaria solani is an airborne fungus and the primary causal agent of potato early blight worldwide. No available fungicides that are both effective and environmentally friendly are usable to control this fungus. Therefore, biological control is a potential approach for its suppression. In this study, Bacillus subtilis strain ZD01's fermentation broth strongly reduced A. solani pathogenicity under greenhouse conditions. The effects of strain ZD01's secondary metabolites on A. solani were investigated. The exposure of A. solani hyphae to the supernatant resulted in swelling and swollen sacs, and the ZD01 supernatant reduced A. solani conidial germination significantly. Matrix-assisted laser desorption/ionization time of flight mass spectrometry and pure product tests revealed that fengycins were the main antifungal lipopeptide substances. To elucidate the molecular mechanism of the fengycins' biological control, RNA sequencing analyses were performed. A transcriptome analysis revealed that 304 and 522 genes in A. solani were differentially expressed after 2-h and 6-h fengycin treatments, respectively. These genes were respectively mapped to 53 and 57 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. In addition, the most enriched KEGG pathway analysis indicated that the inhibitory mechanisms of fengycins against A. solani regulated the expression of genes related to cell wall, cell membrane, transport, energy process, protein synthesis and genetic information. In particular, cell wall and cell membrane metabolism were the main processes affected by fengycin stress. Scanning and transmission electron microscope results revealed hyphal enlargement and a wide range of abnormalities in A. solani cells after exposure to fengycins. Furthermore, fengycins induced chitin synthesis in treated cells, and also caused the capture of cellular fluorescent green labeling and the release of adenosine triphosphate (ATP) from outer membranes of A. solani cells, which may enhance the fengycins ability to alter cell membrane permeability. Thus, this study increases the transcriptome data resources available and supplies a molecular framework for B. subtilis ZD01 inhibition of A. solani HWC-168 through various mechanisms, especially damaging A. solani cell walls and membranes. The transcriptomic insights may lead to an effective control strategy for potato early blight.

Identification and Characterization of Bacillus tequilensis GYUN-300: An Antagonistic Bacterium Against Red Pepper Anthracnose Caused by Colletotrichum acutatum in Korea

Anthracnose is a fungal disease caused by Colletotrichum species and has detrimental effects on many crops, including red pepper. This study used Bacillus tequilensis GYUN-300 (GYUN-300), which exhibit antagonistic activity against the fungal pathogen, Colletotrichum acutatum. This pathogen causes anthracnose that manifests primarily as a fruit rot in red pepper. There have been little efforts to identify antagonistic bacteria from mushrooms; this strain of bacteria was identified as B. tequilensis using BIOLOG and 16S rDNA sequencing analysis. The genetic mechanism underpinning the biocontrol traits of GYUN-300 was characterized using the complete genome sequence of GYUN-300, which was closely compared to related strains. GYUN-300 inhibited mycelial growth and spore germination of C. acutatum under in vitro conditions. Important antagonistic traits, such as siderophore production, solubilization of insoluble phosphate, and production of lytic enzymes (cellulase, protease, and amylase), were observed in GYUN-300, These trains promoted growth in terms of seed germination and vigorous seedling growth compared to the non-treated control. When red pepper fruits were treated with GYUN-300, the preventive and curative effects were 66.6 and 38.3% effective, respectively, in wounded red pepper fruits; there was no difference between the preventive and curative effects in non-wounded red pepper fruits. Furthermore, GYUN-300 was resistant to several commercial fungicides, indicating that GYUN-300 bacterial cells may also be used synergistically with chemical fungicides to increase biocontrol efficiency. Based on in vitro results, GYUN-300 played a role to control anthracnose disease effectively in field conditions when compared to other treatments and non-treated controls. The results from this study provide a better understanding of the GYUN-300 strain as an effective biocontrol agent against red pepper anthracnose; this form of biocontrol provides an environment-friendly alternative to chemical fungicides.

Mechanism of a Volatile Organic Compound (6-Methyl-2-Heptanone) Emitted From Bacillus subtilis ZD01 Against Alternaria solani in Potato

The antagonistic mechanisms of soluble non-volatile bioactive compounds, such as proteins and lipopeptides emitted from Bacillus have been widely studied. However, there are limited studies on the antifungal mechanisms of volatile organic compounds (VOCs) produced by Bacillus against plant fungal diseases. In this study, the antagonistic mechanisms of one specific VOC, 6-methyl-2-heptanone, against Alternaria solani were investigated. To optimize the extraction conditions of headspace solid-phase microextraction, a 50/30-μm divinylbenzene/carboxen/polydimethylsiloxane fiber at 50°C for 40 min was used. For gas chromatography-mass spectrometry using a free fatty acid phase capillary column, 6-methyl-2-heptanone accounted for the highest content, at 22.27%, of the total VOCs from Bacillus subtilis ZD01, which inhibited A. solani mycelial growth strongly in vitro. Therefore, 6-methyl-2-heptanone was selected as the main active chemical to elucidate the action mechanisms against A. solani. Scanning and transmission electron microscopy analyses revealed that after exposure to an EC₅₀ dose of 6-methyl-2-heptanone, A. solani hyphal cells had a wide range of abnormalities. 6-Methyl-2-heptanone also caused the capture of cellular fluorescent green label and the release of adenosine triphosphate (ATP) from outer membranes A. solani cells, which may enhance 6-methyl-2-heptanone ability to reach the cytoplasmic membrane. In addition, 6-methyl-2-heptanone showed strong inhibitory effect on A. solani conidial germination. It also damaged conidial internal structures, with the treated group having collapsed shrunken small vesicles as observed by transmission electron microscopy. Because 6-methyl-2-heptanone showed strong effects on mycelial integrity and conidial structure, the expression levels of related pathogenic genes in A. solani treated with 6-methyl-2-heptanone were investigated. The qRT-PCR results showed that transcriptional expression levels of slt2 and wetA genes were strongly down-regulated after exposure to 6-methyl-2-heptanone. Finally, because identifying the functions of pathogenic genes will be important for the biological control of A. solani, the wetA gene was identified as a conidia-associated gene that plays roles in regulating sporulation yield and conidial maturation. These findings provide further insights into the mechanisms of VOCs secreted by Bacillus against A. solani.

Identification of Volatile Organic Compounds in Extremophilic Bacteria and Their Effective Use in Biocontrol of Postharvest Fungal Phytopathogens

Phytopathogenic fungal growth in postharvest fruits and vegetables is responsible for 20-25% of production losses. Volatile organic compounds (VOCs) have been gaining importance in the food industry as a safe and ecofriendly alternative to pesticides for combating these phytopathogenic fungi. In this study, we analysed the ability of some VOCs produced by strains of the genera Bacillus, Peribacillus, Pseudomonas, Psychrobacillus and Staphylococcus to inhibit the growth of Alternaria alternata, Botrytis cinerea, Fusarium oxysporum, Fusarium solani, Monilinia fructicola, Monilinia laxa and Sclerotinia sclerotiorum, in vitro and in vivo. We analysed bacterial VOCs by using GC/MS and 87 volatile compounds were identified, in particular acetoin, acetic acid, 2,3-butanediol, isopentanol, dimethyl disulphide and isopentyl isobutanoate. In vitro growth inhibition assays and in vivo experiments using cherry fruits showed that the best producers of VOCs, Bacillus atrophaeus L193, Bacillus velezensis XT1 and Psychrobacillus vulpis Z8, exhibited the highest antifungal activity against B. cinerea, M. fructicola and M. laxa, which highlights the potential of these strains to control postharvest diseases. Transmission electron microscopy micrographs of bacterial VOC-treated fungi clearly showed antifungal activity which led to an intense degeneration of cellular components of mycelium and cell death.

Antibiotic Effects of Volatiles Produced by Bacillus tequilensis XK29 against the Black Spot Disease Caused by Ceratocystis fimbriata in Postharvest Sweet Potato

Black spot disease caused by Ceratocystis fimbriata is destructive to the production, transportation, and storage of sweet potato. The antifungal effects of Bacillus tequilensis XK29 against C. fimbriata through volatile organic compounds (VOCs) were evaluated in this study. The activated carbon assay proved that XK29 could exert antibiotic effects through volatiles. By optimizing the wheat seed weight, inoculation method, concentration, volume, and time, the antifungal activity of XK29 was significantly improved. XK29 fumigation inhibited spore formation and germination and changed the cell morphology of C. fimbriata. During the storage of sweet potato tuber roots, XK29 effectively controlled black spot disease and reduced the weight loss and malondialdehyde content. Metabolomic analysis revealed that 21 volatile compounds were released from XK29. Isovaleric acid, isobutyric acid, and 2-methylbutanoic acid effectively inhibited the growth of C. fimbriata. These results indicate that B. tequilensis XK29 has a good potential to be developed as a microbial fumigation agent.

Biocontrol Mechanism of Bacillus subtilis C3 Against Bulb Rot Disease in Fritillaria taipaiensis P.Y.Li

Bulb rot disease has become one of the main diseases that seriously affects the yield and quality of Fritillaria taipaiensis P.Y.Li (F. taipaiensis). In this study, F. taipaiensis was used as the research object to explore the effect and mechanism of Bacillus subtilis C3 in preventing and curing bulb rot. Through isolation and verification of the pathogenic fungi, we determined for the first time that the pathogenic fungus that causes bulb rot in F. taipaiensis is Fusarium oxysporum. The results of the study showed that B. subtilis C3 inhibits the growth of pathogenic fungi, and the inhibition rate is as high as 60%. In the inhibition mechanism, strain C3 inhibits the conidiogenesis of pathogenic fungi and destroys the cell structure of its hyphae, causing protoplast exudation, chromatin concentration, DNA fragmentation, and ultimately cell death. Among the secondary metabolites of C3, antimicrobial proteins and main active components (paeonol, ethyl palmitate, and oxalic acid) inhibited the growth of F. oxysporum. The molecular weight of the antibacterial protein with the highest inhibition rate was approximately 50 kD. The results of a field experiment on the Taibai Mountain F. taipaiensis planting base showed that after the application of strain C3, the incidence of bulb rot in Fritillaria was reduced by 18.44%, and the ratio of bacteria to fungi in the soil increased to 8.21, which verified the control effect of C3 on Fritillaria bulb rot disease. This study provides a theoretical basis for the use of B. subtilis C3 to prevent and control bulb rot in Fritillaria.

Characteristics of the Infection of Tilletia laevis Kühn (syn. Tilletia foetida (Wallr.) Liro.) in Compatible Wheat

Tilletia laevis Kühn (syn. Tilletia foetida (Wallr.) Liro.) causes wheat common bunt, which is one of the most devastating plant diseases in the world. Common bunt can result in a reduction of 80% or even a total loss of wheat production. In this study, the characteristics of T. laevis infection in compatible wheat plants were defined based on the combination of scanning electron microscopy, transmission electron microscopy and laser scanning confocal microscopy. We found T. laevis could lead to the abnormal growth of wheat tissues and cells, such as leakage of chloroplasts, deformities, disordered arrangements of mesophyll cells and also thickening of the cell wall of mesophyll cells in leaf tissue. What's more, T. laevis teliospores were found in the roots, stems, flag leaves, and glumes of infected wheat plants instead of just in the ovaries, as previously reported. The abnormal characteristics caused by T. laevis may be used for early detection of this pathogen instead of molecular markers in addition to providing theoretical insights into T. laevis and wheat interactions for breeding of common bunt resistance.

A Novel Rhizospheric Bacterium: Bacillus velezensis NKMV-3 as a Biocontrol Agent Against Alternaria Leaf Blight in Tomato

A novel strain of Bacillus isolated from rhizosphere has shown to be an excellent biocontrol agent against various plant pathogens. In this study, a first report of a Bacillus strain NKMV-3 which effectively controls Alternaria solani, which cause the early blight disease in tomato. Based on the cultural and molecular sequencing of 16S rRNA gene sequence, the identity of the strain was confirmed as Bacillus velezensis NKMV-3. The presence of the lipopeptide which are antibiotic synthesis genes, namely iturin C, surfactin A and fengycin B and D, was confirmed through gene amplification. In addition, lipopeptides were also confirmed through liquid chromatography. The extract showed inhibitory effect against A. solani in vitro and detached tomato leaf assays. Bacillus velezensis strain NKMV-3-based formulations may provide an effective solution in controlling early blight disease in tomato and other crops.

Analysis of Stored Wheat Grain-Associated Microbiota Reveals Biocontrol Activity among Microorganisms against Mycotoxigenic Fungi

Wheat grains are colonized by complex microbial communities that have the potential to affect seed quality and susceptibility to disease. Some of the beneficial microbes in these communities have been shown to protect plants against pathogens through antagonism. We evaluated the role of the microbiome in seed health: in particular, against mycotoxin-producing fungi. Amplicon sequencing was used to characterize the seed microbiome and determine if epiphytes and endophytes differ in their fungal and bacterial diversity and community composition. We then isolated culturable fungal and bacterial species and evaluated their antagonistic activity against mycotoxigenic fungi. The most prevalent taxa were found to be shared between the epiphytic and endophytic microbiota of stored wheat seeds. Among the isolated bacteria, Bacillus strains exhibited strong antagonistic properties against fungal pathogens with noteworthy fungal load reduction in wheat grain samples of up to a 3.59 log₁₀ CFU/g compared to untreated controls. We also found that a strain of the yeast, Rhodotorula glutinis, isolated from wheat grains, degrades and/or metabolizes aflatoxin B₁, one of the most dangerous mycotoxins that negatively affects physiological processes in animals and humans. The mycotoxin level in grain samples was significantly reduced up to 65% in the presence of the yeast strain, compared to the untreated control. Our study demonstrates that stored wheat grains are a rich source of bacterial and yeast antagonists with strong inhibitory and biodegradation potential against mycotoxigenic fungi and the mycotoxins they produce, respectively. Utilization of these antagonistic microorganisms may help reduce fungal and mycotoxin contamination, and potentially replace traditionally used synthetic chemicals.

Phytostimulation and biocontrol potential of Gram-positive endospore-forming Bacilli

The spore-forming Bacillus and Paenibacillus species represent the phyla of beneficial bacteria for application as agricultural inputs in form of effective phytostimulators, biofertilizers, and biocontrol agents. The members of the genera Bacillus and Paenibacillus isolated from several ecological habitats are been thoroughly dissected for their effective application in the development of sustainable and eco-friendly agriculture. Numerous Bacillus and Paenibacillus species are reported as plant growth-promoting bacteria influencing the health and productivity of the food crops. This review narrates the mechanisms utilized by these species to enhance bioavailability and/or facilitate the acquisition of nutrients by the host plant, modulate plant hormones, stimulate host defense and stress resistance mechanisms, exert antagonistic action against soil and airborne pathogens, and alleviate the plant health. The mechanisms employed by Bacillus and Paenibacillus are seldom mutually exclusive. The comprehensive and systematic exploration of the aforementioned mechanisms in conjunction with the field investigations may assist in the exploration and selection of an effective biofertilizer and a biocontrol agent. This review aims to gather and discuss the literature citing the applications of Bacillus and Paenibacillus in the management of sustainable agriculture.

Antifungal effect of volatile organic compounds produced by Streptomyces salmonis PSRDC-09 against anthracnose pathogen Colletotrichum gloeosporioides PSU-03 in postharvest chili fruit

AIMS

Application of volatile organic compounds (VOCs) from Streptomyces salmonis PSRDC-09 (VOCs PSRDC-09) grown on sterile wheat seeds against chili anthracnose pathogen was investigated in vitro and in vivo.

METHODS AND RESULTS

Among 10 isolates of Colletotrichum species tested, Colletotrichum gloeosporioides PSU-03 was selected as the most aggressive anthracnose pathogenic strain on chili fruit against VOCs produced by Streptomyces species. Among 11 isolates, the strain PSRDC-09 exhibited the highest antifungal activity and was identified as S. salmonis PSRDC-09. The antagonistic mechanism of the VOCs PSRDC-09 on morphological of C. gloeosporioides PSU-03, observed by scanning electron microscope (SEM), revealed the irregular distortions in the fungal hyphae. The effect of inoculum size and spore concentration of S. salmonis PSRDC-09 prepared as a wheat seed inoculum on the suppression of C. gloeosporioides PSU-03 was studied both in vitro and on chili fruit. The optimum inoculum size (45 g 0·31 l^-1 ) and spore concentration (10⁷ spores per ml) of the wheat seed culture of S. salmonis PSRDC-09 exhibited the complete suppression (100% inhibition) on C. gloeosporioides PSU-03. The optimum fumigation period of the VOCs PSRDC-09 (45 g 1·38 l^-1 ) was found to be 24 h. Based on gas chromatography-mass spectrometry (GC-MS) analysis, 14 major VOCs (produced by the strain PSRDC-09) were detected and l-linalool was the main volatile component.

CONCLUSIONS

The results indicated that the VOCs from S. salmonis PSRDC-09 could effectively control the chili anthracnose disease caused by C. gloeosporioides.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings suggest that S. salmonis PSRDC-09 may have the potential to become a promising biofumigant for biocontrol of chili anthracnose disease in the postharvest system.

Characterization of Volatile Organic Compounds Emitted from Endophytic Burkholderia cenocepacia ETR-B22 by SPME-GC-MS and Their Inhibitory Activity against Various Plant Fungal Pathogens

The use of antagonistic microorganisms and their volatile organic compounds (VOCs) to control plant fungal pathogens is an eco-friendly and promising substitute for chemical fungicides. In this work, endophytic bacterium ETR-B22, isolated from the root of Sophora tonkinensis Gagnep., was found to exhibit strong antagonistic activity against 12 fungal pathogens found in agriculture. Strain ETR-B22 was identified as Burkholderia cenocepacia based on 16S rRNA and recA sequences. We evaluated the antifungal activity of VOCs emitted by ETR-B22. The VOCs from strain ETR-B22 also showed broad-spectrum antifungal activity against 12 fungal pathogens. The composition of the volatile profiles was analyzed based on headspace solid phase microextraction (HS-SPME) gas chromatography coupled to mass spectrometry (GC-MS). Different extraction strategies for the SPME process significantly affected the extraction efficiency of the VOCs. Thirty-two different VOCs were identified. Among the VOC of ETR-B22, dimethyl trisulfide, indole, methyl anthranilate, methyl salicylate, methyl benzoate, benzyl propionate, benzyl acetate, 3,5-di-tert-butylphenol, allyl benzyl ether and nonanoic acid showed broad-spectrum antifungal activity, and are key inhibitory compounds produced by strain ETR-B22 against various fungal pathogens. Our results suggest that the endophytic strain ETR-B22 and its VOCs have high potential for use as biological controls of plant fungal pathogens.