Mycosubtilin Produced by Bacillus subtilis ATCC6633 Inhibits Growth and Mycotoxin Biosynthesis of Fusarium graminearum and Fusarium verticillioides

Eco-smart biocontrol strategies utilizing potent microbes for sustainable management of phytopathogenic diseases

Plants have an impact on the economy because they are used in the food and medical industries. Plants are a source of macro- and micronutrients for the health of humans and animals; however, the rise in microbial diseases has put plant health and yield at risk. Because there are insufficient controls, microbial infections annually impact approximately 25 % of the world's plant crops. Alternative strategies, such as biocontrol, are required to fight these illnesses. This review discusses the potential uses of recently discovered microorganisms because they are safe, effective, and unlikely to cause drug resistance. They have no negative effects on soil microbiology or the environment because they are environmentally benign. Biological control enhances indigenous microbiomes by reducing bacterial wilt, brown blotch, fire blight, and crown gall. More research is required to make these biocontrol agents more stable, effective, and less toxic before they can be used in commercial settings.

A "love match" score to compare root exudate attraction and feeding of the plant growth-promoting rhizobacteria Bacillus subtilis, Pseudomonas fluorescens, and Azospirillum brasilense

Introduction

The rhizosphere is the zone of soil surrounding plant roots that is directly influenced by root exudates released by the plant, which select soil microorganisms. The resulting rhizosphere microbiota plays a key role in plant health and development by enhancing its nutrition or immune response and protecting it from biotic or abiotic stresses. In particular, plant growth-promoting rhizobacteria (PGPR) are beneficial members of this microbiota that represent a great hope for agroecology, since they could be used as bioinoculants for sustainable crop production. Therefore, it is necessary to decipher the molecular dialog between roots and PGPR in order to promote the establishment of bioinoculants in the rhizosphere, which is required for their beneficial functions.

Methods

Here, the ability of root exudates from rapeseed (Brassica napus), pea (Pisum sativum), and ryegrass (Lolium perenne) to attract and feed three PGPR (Bacillus subtilis, Pseudomonas fluorescens, and Azospirillum brasilense) was measured and compared, as these responses are directly involved in the establishment of the rhizosphere microbiota.

Results

Our results showed that root exudates differentially attracted and fed the three PGPR. For all beneficial bacteria, rapeseed exudates were the most attractive and induced the fastest growth, while pea exudates allowed the highest biomass production. The performance of ryegrass exudates was generally lower, and variable responses were observed between bacteria. In addition, P. fluorescens and A. brasilense appeared to respond more efficiently to root exudates than B. subtilis. Finally, we proposed to evaluate the compatibility of each plant-PGPR couple by assigning them a "love match" score, which reflects the ability of root exudates to enhance bacterial rhizocompetence.

Discussion

Taken together, our results provide new insights into the specific selection of PGPR by the plant through their root exudates and may help to select the most effective exudates to promote bioinoculant establishment in the rhizosphere.

Antifungal efficacy of Bacillus amyloliquefaciens ZK-9 against Fusarium graminearum and analysis of the potential mechanism of its lipopeptides

Fusarium graminearum is a destructive fungal pathogen that seriously threatens wheat production and quality. In the management of fungal infections, biological control is an environmentally friendly and sustainable approach. Here, the antagonistic strain ZK-9 with a broad antifungal activity was identified as Bacillus amyloliquefaciens. ZK-9 could produce extracellular enzymes such as pectinase, protease, cellulase, and amylase, as well as plant growth-promoting substances including IAA and siderophore. Lipopeptides extracted from strain ZK-9 had the high inhibitory effects on the mycelia of F. graminearum with the minimum inhibitory concentration (MIC) of 0.8 mg/mL. Investigation on the action mechanism of lipopeptides showed they could change the morphology of mycelia, damage the cell membrane, lower the content of ergosterol and increase the relative conductivity of membrane, cause nucleic acid and proteins leaking out from the cells, and disrupt the cell membrane permeability. Furthermore, metabolomic analysis of F. graminearum revealed the significant differences in the expression of 100 metabolites between the lipopeptides treatment group and the control group, which were associated with various metabolic pathways, mainly including amino acid biosynthesis, pentose, glucuronate and glycerophospholipid metabolism. In addition, strain ZK-9 inhibited Fusarium crown rot (FCR) with a biocontrol efficacy of 82.14 % and increased the plant height and root length by 24.23 % and 93.25 %, respectively. Moreover, the field control efficacy of strain ZK-9 on Fusarium head blight (FHB) was 71.76 %, and the DON content in wheat grains was significantly reduced by 69.9 %. This study puts valuable insights into the antifungal mechanism of lipopeptides against F. graminearum, and provides a promising biocontrol agent for controlling F. graminearum.

Classification, application, multifarious activities and production improvement of lipopeptides produced by Bacillus

Lipopeptides, a class of compounds consisting of a peptide ring and a fatty acid chain, are secondary metabolites produced by Bacillus spp. As their hydrophilic and oleophilic properties, lipopeptides are widely used in food, medicine, environment and other industrial or agricultural fields. Compared with artificial synthetic surfactants, microbial lipopeptides have the advantages of low toxicity, high efficiency and versatility, resulting in urgent market demand and broad development prospect of lipopeptides. However, due to the complex metabolic network and precursor requirements of synthesis, the specific and strict synthesis pathway, and the coexistence of multiple homologous substances, the production of lipopeptides by microorganisms has the problems of high cost and low production efficiency, limiting the mass production of lipopeptides and large-scale application in industry. This review summarizes the types of Bacillus-produced lipopeptides and their biosynthetic pathways, introduces the versatility of lipopeptides, and describes the methods to improve the production of lipopeptides, including genetic engineering and optimization of fermentation conditions.

A glycoside hydrolase 30 protein BpXynC of Bacillus paralicheniformis NMSW12 recognized as A MAMP triggers plant immunity response

Bacillus spp. has been widely used as a biocontrol agent to control plant diseases. However, little is known about mechanisms of the protein MAMP secreted by Bacillus spp. Herein, our study reported a glycoside hydrolase family 30 (GH30) protein, BpXynC, produced by the biocontrol bacteria Bacillus paralicheniformis NMSW12, that can induce cell death in several plant species. The results revealed that the recombinant protein triggers cell death in Nicotiana benthamiana in a BAK1-dependent manner and elicits an early defense response, including ROS burst, activation of MAPK cascades, and upregulation of plant immunity marker genes. BpXynC was also found to be a glucuronoxylanase that exhibits hydrolysis activity on xlyan. Two mutants of BpXynC which lost the glucuronoxylanase activity still retained the elicitor activity. The qRT-PCR results of defense-related genes showed that BpXynC induces plant immunity responses via an SA-mediated pathway. BpXynC and its mutants could induce resistance in N. benthamiana against infection by Sclerotinia sclerotiorum and tobacco mosaic virus (TMV). Furthermore, BpXynC-treated tomato fruits exhibited strong resistance to the infection of Phytophthora capsica. Overall, our study revealed that GH30 protein BpXynC can induce plant immunity response as MAMP, which can be further applied as a biopesticide to control plant diseases.

degQ associated with the degS/degU two-component system regulates biofilm formation, antimicrobial metabolite production, and biocontrol activity in Bacillus velezensis DMW1

The gram-positive bacterium Bacillus velezensis strain DMW1 produces a high level of antimicrobial metabolites that can suppress the growth of phytopathogens. We investigated the mechanism used by degQ and the degS/degU two-component system to regulate the biocontrol characteristics of DMW1. When degQ and degU were deleted, the biofilm formation, cell motility, colonization activities, and antifungal abilities of ΔdegQ and ΔdegU were significantly reduced compared to wild-type DMW1. The expression levels of biofilm-related genes (epsA, epsB, epsC, and tasA) and swarming-related genes (swrA and swrB) were all down-regulated. We also evaluated the impact on secondary metabolites of these two genes. The degQ and degU genes reduced surfactin and macrolactin production and up-regulated the production of fengycin, iturin, bacillaene, and difficidin metabolites. The reverse transcription-quantitative PCR results were consistent with these observations. Electrophoretic mobility shift assay and microscale thermophoresis revealed that DegU can bind to the promoter regions of these six antimicrobial metabolite genes and regulate their synthesis. In conclusion, we provided systematic evidence to demonstrate that the degQ and degU genes are important regulators of multicellular behaviour and antimicrobial metabolic processes in B. velezensis DMW1 and suggested novel amenable strains to be used for the industrial production of antimicrobial metabolites.

Broad-spectrum antagonistic potential of Bacillus spp. volatiles against Rhizoctonia solani and Xanthomonas oryzae pv. oryzae

Rhizoctonia solani and Xanthomonas oryzae pv. oryzae (Xoo) are the two major diseases affecting the quality and quantity of rice production. In the current study, volatile organic compounds (VOCs) of Bacillus spp. were used as green biocontrol agents for plant diseases. In in vitro experiments, Bacillus spp. FZB42, NMTD17, and LLTC93-VOCs displayed strong antimicrobial volatile activity with inhibition rates of 76, 66, and 78% for R. solani and 78, 81, and 76% for Xoo, respectively, compared to control. The synthetic VOCs, namely Pentadecane (PDC), Benzaldehyde (BDH), 1,2-Benz isothiazol-3(2H)-one (1,2-BIT), and mixture (MIX) of VOCs showed high volatile activity with inhibition rates of 86, 86, 89, and 92% against R. solani and 81, 81, 82, and 86%, respectively, against Xoo as compared to control. In addition, the scanning and transmission electron microscopes (SEM and TEM) analyses were performed to examine the effect of Bacillus and synthetic VOC treatments on R. solani and Xoo morphology. The analysis revealed the deformed and irregularized morphology of R. solani mycelia and Xoo cells after VOC treatments. The microscopic analysis showed that the rapid inhibition was due to severe oxidative productions inside the R. solani mycelia and Xoo cells. By using molecular docking, it was determined that the synthetic VOCs entered the active binding site of trehalase and NADH dehydrogenase proteins, causing R. solani and Xoo cells to die prematurely and an accumulation of ROS. In the greenhouse experiment, FZB42, NMTD17, and LLTC93-VOCs significantly reduced the lesions of R. solani 8, 7, and 6 cm, and Xoo 7, 6, and 6 cm, respectively, then control. The synthetic VOCs demonstrated that the PDC, BDH, 1,2-BIT, and MIX-VOCs significantly reduced R. solani lesions on leaves 6, 6, 6, and 5 cm and Xoo 6, 5, 5, and 4 cm, respectively, as compared to control. Furthermore, plant defence-related genes and antioxidant enzymes were upregulated in rice plants. These findings provide novel mechanisms by which Bacillus antimicrobial VOCs control plant diseases.

Exogenous Melatonin Regulates Plant-Disease Interaction by Inducing Maize Resistance and Decreasing the Pathogenicity of Fusarium graminearum

Plants cannot avoid environmental challenges and are constantly threatened by diverse biotic and abiotic stresses. However, plants have developed a unique immune system to defend themselves against the invasion of various pathogens. Melatonin, N-acetyl-5-methoxytryptamine has positive physiological effects in plants that are involved in disease resistance. The processes underlying melatonin-induced pathogen resistance in plants are still unknown. The current study explores how melatonin regulates the plant-disease interaction in maize. The results showed that 400 μM melatonin strongly reduced the disease lesion on maize stalks by 1.5 cm and corn by 4.0 cm caused by Fusarium graminearum PH-1. Furthermore, after treatment with melatonin, the plant defense enzymes like SOD significantly increased, while POD and APX significantly decreased compared to the control. In addition, melatonin can also improve maize's innate immunity, which is mediated by melatonin treatments through the salicylic acid signaling pathway, and up-regulate the defense-associated expression of PR1, LOX1, OXR, serPIN, and WIPI genes in maize. Melatonin not only inhibits the disease in the maize stalks and corn, but also down-regulates the deoxynivalenol (DON) production-related expression of genes Tri1, Tri4, Tri5, and Tri6 in maize. Overall, this study sheds new light on the mechanisms by which melatonin regulates antioxidant enzymes and defense-related genes involved in plant immunity to effectively suppress plant diseases.

Synergistic biocontrol of Bacillus subtilis and Pseudomonas fluorescens against early blight disease in tomato

Early blight of tomato caused by Alternaria solani results in significant crop losses. In this study, Bacillus subtilis J3 and Pseudomonas fluorescens J8 were co-cultured as a synthetic microbial community (BCA) for synergistic biocontrol of A. solani, and the inhibition mechanism was investigated. BCA presented an inhibition ration against A. solani at 94.91%, which lowered the disease incidence by 38.26-42.87%; reduced peroxidase, catalase, superoxide dismutase activity of tomatoes by 73.11-90.22%; and promoted the biomass by 66.91-489.21%. With BCA protection, the relative expression of tomato resistance genes (including gPAL2, SWRKY, PR-10, and CHI) in roots and leaves was 12.83-90.70% lower than without protection. BCA also significantly altered the rhizosphere and phyllosphere microbial community. The abundance of potentially beneficial bacteria, including Bacillus, Pseudomonas, Arthrobacter, Lysobacter, and Rhizobium, elevated by 6.58-192.77%. They were negatively correlated with resistance gene expression, indicating their vital involvement in disease control. These results provided essential information on the synergistic biocontrol mechanism of bacteria against pathogens, which could contribute to developing novel biocontrol strategies. KEY POINTS: • Bacillus and Pseudomonas present a synergistic biocontrol effect against A. solani. • Biocontrol prevents pathogen damage and improves tomato growth and systemic resistance. • Beneficial bacteria thrive in the rhizosphere is the key to microbial regulation.

Bacterial and Fungal Biocontrol Agents for Plant Disease Protection: Journey from Lab to Field, Current Status, Challenges, and Global Perspectives

Plants are constantly exposed to various phytopathogens such as fungi, Oomycetes, nematodes, bacteria, and viruses. These pathogens can significantly reduce the productivity of important crops worldwide, with annual crop yield losses ranging from 20% to 40% caused by various pathogenic diseases. While the use of chemical pesticides has been effective at controlling multiple diseases in major crops, excessive use of synthetic chemicals has detrimental effects on the environment and human health, which discourages pesticide application in the agriculture sector. As a result, researchers worldwide have shifted their focus towards alternative eco-friendly strategies to prevent plant diseases. Biocontrol of phytopathogens is a less toxic and safer method that reduces the severity of various crop diseases. A variety of biological control agents (BCAs) are available for use, but further research is needed to identify potential microbes and their natural products with a broad-spectrum antagonistic activity to control crop diseases. This review aims to highlight the importance of biocontrol strategies for managing crop diseases. Furthermore, the role of beneficial microbes in controlling plant diseases and the current status of their biocontrol mechanisms will be summarized. The review will also cover the challenges and the need for the future development of biocontrol methods to ensure efficient crop disease management for sustainable agriculture.

MALDI mass spectrometry-based identification of antifungal molecules from endophytic Bacillus strains with biocontrol potential of Lasiodiplodia theobromae, a grapevine trunk pathogen in Peru

Lasiodiplodia theobromae, a grapevine trunk pathogen, is becoming a significant threat to vineyards worldwide. In Peru, it is responsible for Botryosphaeria dieback in many grapevine-growing areas and it has spread rapidly due to its high transmissibility; hence, control measures are urgent. It is known that some endophytic bacteria are strong inhibitors of phytopathogens because they produce a wide range of antimicrobial molecules. However, studies of antimicrobial features from endophytic bacteria are limited to traditional confrontation methods. In this study, a MALDI mass spectrometry-based approach was performed to identify and characterize the antifungal molecules from Bacillus velezensis M1 and Bacillus amyloliquefaciens M2 grapevine endophytic strains. Solid medium antagonism assays were performed confronting B. velezensis M1 - L. theobromae and B. amyloliquefaciens M2 - L. theobromae for antifungal lipopeptides identification. By a MALDI TOF MS it was possible identify mass spectra for fengycin, iturin and surfactin protoned isoforms. Masses spectrums for mycobacillin and mycosubtilin were also identified. Using MALDI Imaging MS we were able to visualize and relate lipopeptides mass spectra of fengycin (1463.9 m/z) and mycobacillin (1529.6 m/z) in the interaction zone during confrontations. The presence of lipopeptides-synthesis genes was confirmed by PCR. Liquid medium antagonism assays were performed for a proteomic analysis during the confrontation of B. velezensis M1 - L. theobromae. Different peptide sequences corresponding to many antifungal proteins and enzymes were identified by MALDI TOF MS/MS. Oxalate decarboxylase bacisubin and flagellin, reported as antifungal proteins, were identified at 99 % identity through peptide mapping. MALDI mass spectrometry-based identification of antifungal molecules would allow the early selection of endophytic bacteria with antifungal features. This omics tool could lead to measures for prevention of grapevine diseases and other economically important crops in Peru.

Transcriptome Analysis Reveals That C17 Mycosubtilin Antagonizes Verticillium dahliae by Interfering with Multiple Functional Pathways of Fungi

Verticillium wilt is a kind of soil-borne plant fungal disease caused by Verticillium dahliae (Vd). Vd 991 is a strong pathogen causing cotton Verticillium wilt. Previously, we isolated a compound from the secondary metabolites of Bacillus subtilis J15 (BS J15), which showed a significant control effect on cotton Verticillium wilt and was identified as C17 mycosubtilin. However, the specific fungistatic mechanism by which C17 mycosubtilin antagonizes Vd 991 is not clear. Here, we first showed that C17 mycosubtilin inhibits the growth of Vd 991 and affects germination of spores at the minimum inhibitory concentration (MIC). Morphological observation showed that C17 mycosubtilin treatment caused shrinking, sinking, and even damage to spores; the hyphae became twisted and rough, the surface was sunken, and the contents were unevenly distributed, resulting in thinning and damage to the cell membrane and cell wall and swelling of mitochondria of fungi. Flow cytometry analysis with ANNEXINV-FITC/PI staining showed that C17 mycosubtilin induces necrosis of Vd 991 cells in a time-dependent manner. Differential transcription analysis showed that C17 mycosubtilin at a semi-inhibitory concentration (IC50) treated Vd 991 for 2 and 6 h and inhibited fungal growth mainly by destroying synthesis of the fungal cell membrane and cell wall, inhibiting its DNA replication and transcriptional translation process, blocking its cell cycle, destroying fungal energy and substance metabolism, and disrupting the redox process of fungi. These results directly showed the mechanism by which C17 mycosubtilin antagonizes Vd 991, providing clues for the mechanism of action of lipopeptides and useful information for development of more effective antimicrobials.

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.

Profiling of Antimicrobial Metabolites Synthesized by the Endophytic and Genetically Amenable Biocontrol Strain Bacillus velezensis DMW1

The genus Bacillus is one of the most important genera for the biological control of plant diseases that are caused by various phytopathogens. The endophytic Bacillus strain DMW1 was isolated from the inner tissues of potato tubers and exhibited strong biocontrol activity. Based on its whole-genome sequence, DMW1 belongs to the Bacillus velezensis species, and it is similar to the model strain B. velezensis FZB42. 12 secondary metabolite biosynthetic gene clusters (BGCs), including two unknown function BGCs, were detected in the DMW1 genome. The strain was shown to be genetically amenable, and seven secondary metabolites acting antagonistically against plant pathogens were identified by a combined genetic and chemical approach. Strain DMW1 did significantly improve the growth of tomato and soybean seedlings, and it was able to control the Phytophthora sojae and Ralstonia solanacearum that were present in the plant seedlings. Due to these properties, the endophytic strain DMW1 appears to be a promising candidate for comparative investigations performed together with the Gram-positive model rhizobacterium FZB42, which is only able to colonize the rhizoplane. IMPORTANCE Phytopathogens are responsible for the wide spread of plant diseases as well as for great losses of crop yields. At present, the strategies used to control plant disease, including the development of resistant cultivars and chemical control, may become ineffective due to the adaptive evolution of pathogens. Therefore, the use of beneficial microorganisms to deal with plant diseases attracts great attention. In the present study, a new strain DMW1, belonging to the species B. velezensis, was discovered with outstanding biocontrol properties. It showed plant growth promotion and disease control abilities that are comparable with those of B. velezensis FZB42 under greenhouse conditions. According to a genomic analysis and a bioactive metabolites analysis, genes that are responsible for promoting plant growth were detected, and metabolites with different antagonistic activities were identified. Our data provide a basis for DMW1 to be further developed and applied as a biopesticide, which is similar to the closely related model strain FZB42.

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.

Transcriptome and metabolome analyses reveal that Bacillus subtilis BS-Z15 lipopeptides mycosubtilin homologue mediates plant defense responses

Microbial-plant interactions protect plants from external stimuli, releasing various elicitor that activate the plants defense response and regulate its growth. Bacillus subtilis BS-Z15 was screened from cotton inter-rhizosphere soil, antagonized various plant pathogens, and protected cotton against Verticillium dahliae. This study showed that the BS-Z15 lipopeptide mycosubtilin homologue could act as an elicitor to induce systemic resistance (ISR) in plants. Mycosubtilin homologue induced ROS burst and deposition, callose deposition, MAPK cascade phosphorylation, and up-regulated PR1 and PDF1.2 gene expression in Arabidopsis seedlings, moreover enhanced resistance of Arabidopsis to Pseudomonas syringae pv. Tomato DC3000 (Pst DC3000) and V. dahliae. Transcriptome analysis was then used to evaluate the impact of mycosubtilin homologue on plant gene expression control. Mycosubtilin homologues activated Arabidopsis ISR on genes in metabolic pathways such as Arabidopsis plant-pathogen interactions, phenylpropanoid biosynthesis, MAPK signaling pathway, and phytohormone signaling. These analyses revealed that mycosubtilin homologues mediate the regulation of plant systemic resistance and growth and development by affecting related metabolites in glycolysis and gluconeogenesis, pentose phosphate pathway, tricarboxylic acid cycle, and amino acid metabolism in Arabidopsis. These findings confirmed that a mycosubtilin homologue could trigger the initiation of the Arabidopsis ISR by interacting with a variety of PTI components and transcriptional metabolic signaling pathways.

Isolation and Characterization of Two New Deoxynivalenol-Degrading Strains, Bacillus sp. HN117 and Bacillus sp. N22

Deoxynivalenol (DON), produced by Fusarium species, is one of the most common trichothecenes detected in cereals pre- and post-harvest, which poses a great threat to the health of livestock and human beings due to its strong toxicity. In this study, we isolated and characterized two DON-degrading bacterial strains, Bacillus sp. HN117 and Bacillus sp. N22. Both strains could degrade DON efficiently in a wide range of temperatures (from 25 °C to 42 °C) and concentrations (from 10 mg/L to 500 mg/L). After optimization of the degradation conditions, 29.0% DON was eliminated by HN117 in 72 h when it was incubated with 1000 mg/L DON; meanwhile, the DON degradation rate of N22 was boosted notably from 7.41% to 21.21% within 120 h at 500 mg/L DON. Degradation products analysis indicated HN117 was able to transform DON into a new isomer M-DOM, the possible structure of which was deduced based on LC-MS and NMR analysis, and N22 could convert DON into potential low-toxic derivatives norDON E and 9-hydroxymethyl DON lactone. These two strains have the potential to be developed as new biodegrading agents to control DON contamination in food and feed industries.

Bacillus spp.-Mediated Growth Promotion of Rice Seedlings and Suppression of Bacterial Blight Disease under Greenhouse Conditions

Rice (Oryza sativa L.) is a major cereal and staple food crop worldwide, and its growth and production are affected by several fungal and bacterial phytopathogens. Bacterial blight (BB) is one of the world's most devastating rice diseases, caused by Xanthomonas oryzae pv. oryzae (Xoo). In the current study, Bacillus atrophaeus FA12 and B. cabrialesii FA26 were isolated from the rice rhizosphere and characterized as having broad-range antifungal and antibacterial activities against various phytopathogens, including Xoo. In addition, the selected strains were further evaluated for their potent rice growth promotion and suppression efficacy against BB under greenhouse conditions. The result shows that FA12 and FA26, applied as seed inoculants, significantly enhanced the vigor index of rice seedlings by 78.89% and 108.70%, respectively. Suppression efficacy against BB disease by FA12 and FA26 reached up to 59.74% and 54.70%, respectively, in pot experiments. Furthermore, MALDI-TOF MS analysis of selected strains revealed the masses ranged from m/z 1040 to 1540, representing that iturins and fengycin are the major antimicrobial compounds in the crude extracts, which might have beneficial roles in rice defence responses against BB. In conclusion, FA12 and FA26 possess broad-range antagonistic activity and have the capability to promote plant growth traits. More importantly, applying these strains has a high potential for implementing eco-friendly, cost-effective, and sustainable management practices for BB disease.

Rhamnolipids and fengycins, very promising amphiphilic antifungal compounds from bacteria secretomes, act on Sclerotiniaceae fungi through different mechanisms

Rhamnolipids (RLs) and fengycins (FGs) are amphiphilic lipid compounds from bacteria secretomes proposed to replace synthetic pesticides for crop protection. They both display plant defense triggering properties and direct antimicrobial activities. In particular, they have well reported antifungal effects against phytopathogenic fungi. RLs and FGs are considered to act through a direct interaction with membrane lipids and a destabilization of microorganism plasma membrane, thereby limiting the risk of resistance emergence. The main objective of this work was to gain insights in the antimycelial mode of action of these metabolites to promote them as environment and human health friendly biocontrol solutions. Their biocidal effects were studied on two Sclerotiniaceae fungi responsible for diseases in numerous plant species worldwide. We show here that different strains of Botrytis cinerea and Sclerotinia sclerotiorum have opposite sensitivities to RLs and FGs on plate experiments. Overall, B. cinerea is more sensitive to FGs while S. sclerotiorum is more sensitive to RLs. Electron microscopy observations demonstrated that RLs induce mycelial destructuring by asperities emergence and hyphal fusions whereas FGs promote swelling and formation of vesicle-like structures due to vacuole fusions and autophagy. Permeability studies, phosphatidylserine externalization and reactive oxygen species production assessments showed a programmed cell death triggering by RLs at medium concentrations (until 50 μg mL⁻¹) and necrosis characteristics at higher concentration. Programmed cell death was always observed on hyphae treated with FGs. Quantifications of mycelial ergosterol content indicated that a higher ergosterol rate in S. sclerotiorum correlates with increasing sensitivity to RLs. Oppositely, a lower ergosterol rate in B. cinerea correlates with increasing sensitivity to FGs, which was confirmed by ergosterol biosynthesis inhibition with tebuconazole. This gain of knowledge will help to better understand the mode of action of RLs and FGs to fight specific plant fungal diseases.

Enhancement of nitrogen use efficiency through agronomic and molecular based approaches in cotton

Cotton is a major fiber crop grown worldwide. Nitrogen (N) is an essential nutrient for cotton production and supports efficient crop production. It is a crucial nutrient that is required more than any other. Nitrogen management is a daunting task for plants; thus, various strategies, individually and collectively, have been adopted to improve its efficacy. The negative environmental impacts of excessive N application on cotton production have become harmful to consumers and growers. The 4R's of nutrient stewardship (right product, right rate, right time, and right place) is a newly developed agronomic practice that provides a solid foundation for achieving nitrogen use efficiency (NUE) in cotton production. Cropping systems are equally crucial for increasing production, profitability, environmental growth protection, and sustainability. This concept incorporates the right fertilizer source at the right rate, time, and place. In addition to agronomic practices, molecular approaches are equally important for improving cotton NUE. This could be achieved by increasing the efficacy of metabolic pathways at the cellular, organ, and structural levels and NUE-regulating enzymes and genes. This is a potential method to improve the role of N transporters in plants, resulting in better utilization and remobilization of N in cotton plants. Therefore, we suggest effective methods for accelerating NUE in cotton. This review aims to provide a detailed overview of agronomic and molecular approaches for improving NUE in cotton production, which benefits both the environment and growers.

Toxicity of Bacillus thuringiensis Strains Derived from the Novel Crystal Protein Cry31Aa with High Nematicidal Activity against Rice Parasitic Nematode Aphelenchoides besseyi

The plant parasitic nematode, Aphelenchoides besseyi, is a serious pest causing severe damage to various crop plants and vegetables. The Bacillus thuringiensis (Bt) strains, GBAC46 and NMTD81, and the biological strain, FZB42, showed higher nematicidal activity against A. besseyi, by up to 88.80, 82.65, and 75.87%, respectively, in a 96-well plate experiment. We screened the whole genomes of the selected strains by protein-nucleic acid alignment. It was found that the Bt strain GBAC46 showed three novel crystal proteins, namely, Cry31Aa, Cry73Aa, and Cry40ORF, which likely provide for the safe control of nematodes. The Cry31Aa protein was composed of 802 amino acids with a molecular weight of 90.257 kDa and contained a conserved delta-endotoxin insecticidal domain. The Cry31Aa exhibited significant nematicidal activity against A. besseyi with a lethal concentration (LC₅₀) value of 131.80 μg/mL. Furthermore, the results of in vitro experiments (i.e., rhodamine and propidium iodide (PI) experiments) revealed that the Cry31Aa protein was taken up by A. besseyi, which caused damage to the nematode's intestinal cell membrane, indicating that the Cry31Aa produced a pore-formation toxin. In pot experiments, the selected strains GBAC46, NMTD81, and FZB42 significantly reduced the lesions on leaves by up to 33.56%, 45.66, and 30.34% and also enhanced physiological growth parameters such as root length (65.10, 50.65, and 55.60%), shoot length (68.10, 55.60, and 59.45%), and plant fresh weight (60.71, 56.45, and 55.65%), respectively. The number of nematodes obtained from the plants treated with the selected strains (i.e., GBAC46, NMTD81, and FZB42) and A. besseyi was significantly reduced, with 0.56, 0.83., 1.11, and 5.04 seedling mL^-1 nematodes were achieved, respectively. Moreover, the qRT-PCR analysis showed that the defense-related genes were upregulated, and the activity of hydrogen peroxide (H₂O₂) increased while malondialdehyde (MDA) decreased in rice leaves compared to the control. Therefore, it was concluded that the Bt strains GBAC46 and NMTD81 can promote rice growth, induce high expression of rice defense-related genes, and activate systemic resistance in rice. More importantly, the application of the novel Cry31Aa protein has high potential for the efficient and safe prevention and green control of plant parasitic nematodes.

Characterization of subtilosin gene in wild type Bacillus spp. and possible physiological role

In a designed study to screen for antimicrobial exhibiting bacteria using molecular aspects, Bacillus species were considered to investigate antibiotic biosynthesis genes. 28 bacterial strains and 3 induced mutants were screened for the presence of subtilosin gene (sbo) and subtilosin through PCR and Mass spectrometry respectively. Sbo gene was detected in 16 out of 28 Bacillus strains. The results from gene sequences deliberated by multiple sequence alignments revealed high-level homology to the sequences of the sbo-alb gene locus of B. subtilis 168 and the other limited reported strains. Hence, this report provided additional strains to support the idea of subtilosin gene predominance amongst Bacillus strains isolated from environment and to find different species containing homologous genes, furthermore the utilization of its conserved region as a means of identifying Bacillus spp. that produce subtilosin. This is the first report to confirm the detection of subtilosin production from B. amyloliquefaciens.

Characterization of subtilosin gene in wild type Bacillus spp. and possible physiological role

In a designed study to screen for antimicrobial exhibiting bacteria using molecular aspects, Bacillus species were considered to investigate antibiotic biosynthesis genes. 28 bacterial strains and 3 induced mutants were screened for the presence of subtilosin gene (sbo) and subtilosin through PCR and Mass spectrometry respectively. Sbo gene was detected in 16 out of 28 Bacillus strains. The results from gene sequences deliberated by multiple sequence alignments revealed high-level homology to the sequences of the sbo-alb gene locus of B. subtilis 168 and the other limited reported strains. Hence, this report provided additional strains to support the idea of subtilosin gene predominance amongst Bacillus strains isolated from environment and to find different species containing homologous genes, furthermore the utilization of its conserved region as a means of identifying Bacillus spp. that produce subtilosin. This is the first report to confirm the detection of subtilosin production from B. amyloliquefaciens.