Optimizing mass production of Trichoderma asperelloides by submerged liquid fermentation and its antagonism against Sclerotinia sclerotiorum

Development of Composite Microbial Products for Managing Pine Wilt Disease in Infected Wood Stumps

Wood-decay fungi, including white- and brown-decay fungi, are well known for their ability to degrade lignin and cellulose, respectively. The combined use of these fungi can increase the decomposition of woody substrates. Research has indicated that these fungi also exhibit inhibitory effects against Bursaphelenchus xylophilus, the causative agent of pine wilt disease (PWD). In this study, we investigated a composite microbial formulation that efficiently decomposes pine wood while inhibiting B. xylophilus. We initially established a correlation between the degradation rate of wood blocks and fungal biomass, underscoring the necessity of optimizing biomass for effective treatment. A systematic approach involving a one-way test, a Plackett-Burman design, a steepest ascent experiment, and a Box-Behnken design, was employed to optimize the fermentation process. Validation trials were conducted in a 10-L fermenter. The bioagent's efficacy and safety were assessed through field applications in a forest, with a focus on wood degradation capacity and B. xylophilus mortality rate. Additionally, the environmental impact of the microbial products was evaluated by analysing soil quality around treated areas to ensure that the formulation did not adversely affect soil health.

Immobilization of Coprinus comatus with magnetic alginate hydrogel microsphere for improving the antioxidant activity of fermentation products

Coprinus comatus is an edible mushroom and its fermented product possesses antioxidant activity. In this study, to further enhance the antioxidant activity and improve the reusability of the strain, calcium alginate hydrogel was used as the carrier for embedding and immobilizing Coprinus comatus. The effects of CaCl2 concentration, sodium alginate concentration, microsphere diameter, and the amount of magnetic particle on the antioxidant activity of fermented products were investigated. The results showed that the magnetic immobilized microsphere prepared by 2.50% CaCl2, 2.00% sodium alginate and 0.50% Fe3O4 had the best fermentation antioxidant activity (EC50 was 0.43 ± 0.01 mg/mL) when the diameter was 5 mm, which increased by 24.56% compared to the initial activity. Besides, the microsphere showed strong reusability, the antioxidant activity was still better than the free strain after being used five times. This study not only enhanced the antioxidant activity of Coprinus comatus fermented product through immobilization, but also provided an effective method for microbial fermentation.

Agricultural Pest Management: The Role of Microorganisms in Biopesticides and Soil Bioremediation

Pesticide use in crops is a severe problem in some countries. Each country has its legislation for use, but they differ in the degree of tolerance for these broadly toxic products. Several synthetic pesticides can cause air, soil, and water pollution, contaminating the human food chain and other living beings. In addition, some of them can accumulate in the environment for an indeterminate amount of time. The agriculture sector must guarantee healthy food with sustainable production using environmentally friendly methods. In this context, biological biopesticides from microbes and plants are a growing green solution for this segment. Several pests attack crops worldwide, including weeds, insects, nematodes, and microorganisms such as fungi, bacteria, and viruses, causing diseases and economic losses. The use of bioproducts from microorganisms, such as microbial biopesticides (MBPs) or microorganisms alone, is a practice and is growing due to the intense research in the world. Mainly, bacteria, fungi, and baculoviruses have been used as sources of biomolecules and secondary metabolites for biopesticide use. Different methods, such as direct soil application, spraying techniques with microorganisms, endotherapy, and seed treatment, are used. Adjuvants like surfactants, protective agents, and carriers improve the system in different formulations. In addition, microorganisms are a tool for the bioremediation of pesticides in the environment. This review summarizes these topics, focusing on the biopesticides of microbial origin.

Innovative sustainable bioreactor-in-a-granule formulation of Trichoderma asperelloides

The advancement of fungal biocontrol agents depends on replacing cereal grains with low-cost agro-industrial byproducts for their economical mass production and development of stable formulations. We propose an innovative approach to develop a rice flour-based formulation of the beneficial biocontrol agent Trichoderma asperelloides CMAA1584 designed to simulate a micro-bioreactor within the concept of full biorefinery process, affording in situ conidiation, extended shelf-life, and effective control of Sclerotinia sclerotiorum, a devastating pathogen of several dicot agricultural crops worldwide. Rice flour is an inexpensive and underexplored byproduct derived from broken rice after milling, capable of sustaining high yields of conidial production through our optimized fermentation-formulation route. Conidial yield was mainly influenced by nitrogen content (0.1% w/w) added to the rice meal coupled with the fermentor type. Hydrolyzed yeast was the best nitrogen source yielding 2.6 × 109 colony-forming units (CFU)/g within 14 days. Subsequently, GControl, GLecithin, GBreak-Thru, GBentonite, and GOrganic compost+Break-Thru formulations were obtained by extrusion followed by air-drying and further assessed for their potential to induce secondary sporulation in situ, storage stability, and efficacy against Sclerotinia. GControl, GBreak-Thru, GBentonite, and GOrganic compost+Break-Thru stood out with the highest number of CFU after sporulation upon re-hydration on water-agar medium. Shelf-life of formulations GControl and GBentonite remained consistent for > 3 months at ambient temperature, while in GBentonite and GOrganic compost+Break-Thru formulations remained viable for 24 months during refrigerated storage. Formulations exhibited similar efficacy in suppressing the myceliogenic germination of Sclerotinia irrespective of their concentration tested (5 × 104 to 5 × 106 CFU/g of soil), resulting in 79.2 to 93.7% relative inhibition. Noteworthily, all 24-month-old formulations kept under cold storage successfully suppressed sclerotia. This work provides an environmentally friendly bioprocess method using rice flour as the main feedstock to develop waste-free granular formulations of Trichoderma conidia that are effective in suppressing Sclerotinia while also improving biopesticide shelf-life. KEY POINTS: • Innovative "bioreactor-in-a-granule" system for T. asperelloides is devised. • Dry granules of aerial conidia remain highly viable for 24 months at 4 °C. • Effective control of white-mold sclerotia via soil application of Trichoderma-based granules.

Optimization of liquid fermentation conditions for Coprinus comatus to enhance antioxidant activity

Coprinus comatus is an edible and medicinal fungus. In this study, the antioxidant activity of the fermentation product of C. comatus was investigated through optimization of fermentation process. The results indicated that the fermentation product of C. comatus had obvious scavenging ability for 2,2'-Azino-bis(3-ethylbenzothiazoline)-6-sulphonic acid (ABTS) free radical. The EC50 of the n-butanol extract from the fermentation product on ABTS·+ was 0.65 ± 0.02 mg/mL. On this basis, the liquid fermentation conditions of C. comatus were optimized through single factor and response surface optimization experiments according to the scavenging ability of ABTS·+ to improve the antioxidant capacity of the fermentation product. The results showed that when the 14% of C. comatus was fermented in a culture medium with a C/N ratio of 48:1 for 6 days, the ABTS·+ scavenging ability was the strongest, and the EC50 of n-butanol extract was 0.57 ± 0.01 mg/mL, which was 12.31% higher than the initial activity. This study laid the foundation for the development of C. comatus.

Trichoderma koningiopsis Tk905: an efficient biocontrol, induced resistance agent against banana Fusarium wilt disease and a potential plant-growth-promoting fungus

Fusarium oxysporum f. sp. cubense tropical race 4 (FocTR4) is a devastating phytopathogen responsible for significant losses in banana production worldwide. Trichoderma and other biocontrol agents (BCAs) have been used as suitable disease control methods for banana Fusarium wilt. In this study, the endophytic T. koningiopsis Tk905 strain was isolated from the roots of dendrobe plants and identified utilizing morphological and molecular analyses. Antifungal activity tests revealed that Tk905 effectively inhibited mycelial growth with inhibition rates ranging from 26.52 to 75.34%. Additionally, Tk905 covered the pathogen mycelia, and spores were observed on or around the pathogen hyphae. The average root and shoot fresh weights and plant height, of Tk905-inoculated plants were significantly higher than those of the untreated plants. Furthermore, Tk905 treatment significantly increased the activity of antioxidant enzymes, such as catalase (CAT), phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), and peroxidase (POD), suggesting that Tk905 may enhance plant defence systems by activating their antioxidant mechanisms. Most importantly, Tk905-treated plants inoculated by three methods exhibited significantly lower disease incidence and severity than untreated plants. The protective effects of Tk905 against FocTR4 infection were not only observed in the early stages of infection but persisted throughout the experiment, suggesting that T. koningiopsis Tk905 can provide long-lasting protection against Fusarium wilt.

The participation of vacuoles and the regulation of various metabolic pathways under acid stress promote the differentiation of chlamydospore in Trichoderma harzianum T4

AIMS

Chlamydospores are a special, differentiated type with high environmental resistance. Consequently, the chlamydospores of Trichoderma harzianum T4 can used to industrialize the latter. This study aimed to investigate the key factors affecting the sporulation type of T. harzianum T4 and the mechanisms underlying this effect.

METHODS AND RESULTS

In the liquid fermentation of T. harzianum T4, ammonium sulfate (AS) inhibited conidia formation and chlamydospore production. Fermentation tests revealed that acid stress induced sporulation type alteration. Transcriptomic analysis was used to evaluate the adaptation strategy and mechanism underlying spore type alteration under acid stress. The fermentation experiments involving the addition of amino acids revealed that branched-chain amino acids benefited conidia production, whereas β-alanine benefited chlamydospore production. Confocal microscope fluorescence imaging and chloroquine intervention demonstrated that vacuole function was closely related to chlamydospore production.

CONCLUSION

The sporulation type of T. harzianum T4 can be controlled by adjusting the fermentation pH. T. harzianum T4 cells employ various self-protection measures against strong acid stress, including regulating their metabolism to produce a large number of chlamydospores for survival.

Impact of Growth Conditions on the Viability of Trichoderma asperellum during Storage

As excellent biocontrol agents and plant growth promoters, Trichoderma species are agriculturally important. Trichoderma spp. cultures can be produced using solid-state or submerged cultivation, the latter being much less labor intensive and easier to control and automate. The aim of the study was to investigate the ability to increase the shelf-life of T. asperellum cells by optimizing cultivation media and upscaling the submerged cultivation process. Four different cultivation media were used with or without the addition of Tween 80 and stored with or without incorporation into peat, and viability, expressed as CFU/g, was assessed during one year of storage in an industrial warehouse. The addition of Tween 80 had a positive effect on the biomass yield. The culture medium played a major role in the ability of the mycelium to produce spores, which in turn influenced the amount of CFU. This effect was less pronounced when the biomass was mixed with peat prior to storage. A procedure that increases the number of CFU in a peat-based product formulation is recommended, namely, incubation of the mixture at 30 °C for 10 days prior to storage at 15 °C over an extended period of time.

Using green waste as substrate to produce biostimulant and biopesticide products through solid-state fermentation

Although the use of green waste as a substrate in different types of microbial bioprocessing has a major impact on improving green waste valorization, very little information has been provided on this issue. The purpose of this paper is to study the feasibility of using green waste to produce a biostimulant (Indole-3-acetic acid (IAA)) and biopesticide (conidial spore) through solid-state fermentation. Trichoderma harzianum was selected as the inoculum of the process and the green waste was a mixture of grass clippings and pruning waste. An experiment was designed to study the effect of tryptophan concentration, proportion of grass and pruning waste, and substrate moisture on IAA and spore production. The results show that washing and using phosphate buffer has a beneficial effect on green waste quality in terms of bioproduction. The maximum IAA and spore productions reported in the current study were 101.46 µg g^-1 dry matter and 3.03 × 10⁹ spore g^-1 dry matter, respectively. According to the results, IAA production increases with a higher amount of tryptophan and grass. However, the number of spores increased with lower amounts of tryptophan and grass. The model suggested the following optimized parameters for the production of spores and IAA: tryptophan 0.45 %, grass 61 %, and moisture 74 %. The effect of fermentation time was also studied, and the results show that the maximum IAA and spore production was obtained on days 3 and 7, respectively.

Digital gene expression profiling of the transcriptional response to Sclerotinia sclerotiorum and its antagonistic bacterium Bacillus amyloliquefaciens in soybean

Soybean Sclerotinia stem rot caused by Sclerotinia sclerotiorum is a common disease in soybean, and effective biological control is urgently needed. We have previously confirmed that Bacillus amyloliquefaciens can effectively antagonize S. sclerotiorum in a plate competition experiment and a soybean seedling inoculation experiment. In this study, the mechanisms underlying plant death caused by S. sclerotiorum and soybean resistance to S. sclerotiorum induced by B. amyloliquefaciens were evaluated. The stems of potted soybean seedlings were inoculated with S. sclerotiorum (Gm-Ss), B. amyloliquefaciens (Gm-Ba), and their combination (Gm-Ba-Ss), using scratch treatments as a control, followed by dual RNA sequencing and bioinformatics analyses. Global gene expression levels in the Gm-Ss treatment were much lower than those in the Gm-Ba, Gm-Ba-Ss, and Gm groups, suggesting that S. sclerotiorum strongly inhibited global gene expression in soybean. In a pairwise comparison of Gm-Ss vs. Gm, 19983 differentially expressed genes (DEGs) were identified. Down-regulated DEGs were involved in various KEGG pathways, including ko01110 (biosynthesis of secondary metabolites), ko01100 (metabolic pathways), ko01120 (microbial metabolism in diverse environments), ko00500 (starch and sucrose metabolism), and ko04075 (plant hormone signal transmission), suggesting that S. sclerotiorum inoculation had a serious negative effect on soybean metabolism. In Gm-Ba vs. Gm, 13091 DEGs were identified, and these DEGs were significantly enriched in ko03010 (ribosome) and ko03008 (ribosome biogenesis in eucaryotes). Our results suggest that B. amyloliquefaciens increases the expression of genes encoding the ribosomal subunit, promotes cell wall biogenesis, and induces systemic resistance. S. sclerotiorum strongly inhibited metabolism in soybean, inhibited the synthesis of the cytoskeleton, and induced the up-regulation of programmed death and senescence-related genes via an ethylene signal transduction pathway. These results improve our understanding of S. sclerotiorum-induced plant death and soybean resistance to S. sclerotiorum induced by B. amyloliquefaciens and may contribute to the improvement of strategies to avoid yield losses.

Approaches for the establishment of optimized co-culture system of multiple Trichoderma strains for culture metabolites highly effective in cucumber growth promotion

In most cases, co-culture of Trichoderma and other microorganism principally takes advantage of biological control of plant diseases, which is superior to axenic culture. However, the approach to establish the optimal co-culture system of multiple Trichoderma strains was less studied, particularly for high production of microbial metabolites synergistically to promote plant growth and antagonistic activity against pathogens. The inoculation technique, fermentation kinetic modeling and response surface methodology were used to obtain the optimal inoculum sequence, fermentation time and co-culture nutrient formula. It was demonstrated that co-culture metabolites of Trichoderma strains obtained by simultaneous inoculation were more effective than those by sequence inoculation in promoting cucumber seedling growth. Furthermore, the optimal fermentation time was determined at 96–120 h by evaluating fermentation kinetic model, the activities of inhibitory potential of pathogenic Fusarium and cucumber seedling hypocotyl growth. Interestingly, the optimized nutrient formula was set to make co-culture metabolites of Trichoderma strains more effective in the plant growth promotion, which was determined through the assessment of cucumber test-tube plantlet. The components and each concentration in the optimized medium were confirmed at corn flour 16.22 g⋅L–1, potassium hydrogen phosphate 1.13 g⋅L–1, tryptophan 0.154 g⋅L–1, seaweed residue 30 g⋅L–1, ferrous sulfate heptahydrate 1 g⋅L–1 and ammonium sulfate 1.5 g⋅L–1. The hypocotyl length increased in the treatment with co-culture metabolites from the optimal medium by 2.3-fold compared with control. Thus, the results provide an optimal co-culture system of Trichoderma multiple strains aiming to produce high activity of metabolites in plant growth promotion.

Antifungal compounds, GC-MS analysis and toxicity assessment of methanolic extracts of Trichoderma species in an animal model

Fungi of the genus Trichoderma have been marketed for the management of diseases of crops. However, some Trichoderma species may produce toxic secondary metabolites and it should receive due attention to ensure human safety. In this study, we investigated the in vitro antagonistic potential of T. asperellum AU131 and T. longibrachiatum AU158 as microbial biocontrol agents (MBCAs) against Fusarium xylarioides and the associated antagonistic mechanism with bioactive substances. Swiss albino mice were used to evaluate the in vivo toxicity and pathogenicity of T. asperellum AU131 and T. longibrachiatum AU158 methanolic extracts and spore suspensions, respectively, in a preliminary safety assessment for use as biofungicides. Gas Chromatography-Mass Spectrometry (GC-MS) was used to profile volatile organic metabolites (VOCs) present in the methanolic extracts. The agar diffusion assay of the methanolic extracts from both T. asperellum AU131 and T. longibrachiatum AU158 were effective at a concentration of 200 μg/mL (1×10⁷ spores/mL), causing 62.5%, and 74.3% inhibition, respectively. A GC-MS analysis of methanolic extracts from both bioagents identified 23 VOCs which classified as alcohols, acids, sesquiterpenes, ketones and aromatic compounds. The oral administration of methanolic extracts and spore suspensions of each Trichoderma species to female Swiss albino mice over 14 days did not show any significant signs of toxicity, mortality or changes to body weight. It can be concluded that the tested spore suspensions and methanolic extracts were not pathogenic or toxic, respectively, when administered to Swiss albino mice at various doses.

Dual RNA Sequencing Analysis of Bacillus amyloliquefaciens and Sclerotinia sclerotiorum During Infection of Soybean Seedlings by S. sclerotiorum Unveils Antagonistic Interactions

Soybean Sclerotinia stem rot is caused by Sclerotinia sclerotiorum infection, which causes extensive and severe damage to soybean production. Here, we isolated and patented a Bacillus amyloliquefaciens strain, and used it to verify the antagonistic effect of B. amyloliquefaciens on S. sclerotiorum and to explore the possible underlying mechanism. First, we conducted a plate confrontation experiment using the two microbes. Then, inoculation of soybean (Glycine max) seedlings with S. sclerotiorum (Gm-Ss), B. amyloliquefaciens (Gm-Ba), and their combination (Gm-Ba-Ss) was performed, followed by dual RNA sequencing analysis. Plate confrontation and inoculation experiments showed that B. amyloliquefaciens significantly antagonized S. sclerotiorum growth. The average number of fragments per kilobase of transcript per million fragments mapped of S. sclerotiorum transcripts in Gm-Ss and Gm-Ba-Ss inoculation treatments were 117.82 and 50.79, respectively, indicating that B. amyloliquefaciens strongly inhibited gene expression of S. sclerotiorum. In contrast, the average number of fragments per kilobase of transcript per million fragments mapped of B. amyloliquefaciens transcripts in Gm-Ba and Gm-Ba-Ss inoculation treatments were 479.56 and 579.66, respectively, indicating that S. sclerotiorum promoted overall gene expression in B. amyloliquefaciens. For S. sclerotiorum, 507 upregulated and 4,950 downregulated genes were identified among 8,975 genes in the paired comparison Gm-Ba-Ss vs. Gm-Ss. These differentially expressed genes (DEGs) were significantly enriched in the ribosome (ko03010) KEGG pathway. Additionally, for B. amyloliquefaciens, 294 upregulated and 178 downregulated genes were identified among all 3,154 genes in the paired comparison Gm-Ba-Ss vs. Gm-Ba, and these DEGs were mainly and significantly enriched in metabolism-related KEGG pathways, including the citrate cycle (ko00020) and carbon metabolism (ko01200). We concluded that B. amyloliquefaciens inhibits the expression of genes encoding the ribosomal subunit of S. sclerotiorum, resulting in protein synthesis inhibition in S. sclerotiorum, and thus had a strong antagonistic effect on the fungus. This study provides a scientific basis for the biological control of S. sclerotiorum by B. amyloliquefaciens.

Bio-based composite granules with simultaneous biocontrol and phosphorus fertilization roles: outcomes from a lab-scale in-vitro assessment

The use of phosphate rocks as low-solubility phosphorus fertilizers has been promoted to reduce the environmental impacts of agriculture, but adequate nutrient uptake by plants depends on solubilization of the rock, driven by soil microorganisms. Here, investigation was made of the microbial solubilization of low-solubility phosphate rocks, together with simultaneous bioprotective action involving the biocontrol of microorganisms. The aim was to enhance function and value by delivering two effects using a single bio-based product, in accordance with the concept of a "bioreactor-in-a-granule" system. A composite structure was developed, based on a starch matrix, comprising a combination of Trichoderma asperelloides, as a biocontrol agent, and Aspergillus niger, as an acidulant. A significant increase of up to 150% in P solubilization was achieved, indicating the positive effect of the microorganism-composite interaction. In vitro assays showed that the ability of T. asperelloides to inhibit Fusarium oxysporum mycelial growth was maintained in the presence of A. niger. Moreover, the estimated cost of the composite granule (0.35 US$/kg of product on a dry basis) revealed competitive. The results indicated that the association of T. asperelloides and A. niger is an effective way to increase nutrient availability and to inhibit plant pathogens, opening up possibilities for the design of multifunctional bio-based fertilizer composites. This article is protected by copyright. All rights reserved.

The Endophytic Strain Trichoderma asperellum 6S-2: An Efficient Biocontrol Agent against Apple Replant Disease in China and a Potential Plant-Growth-Promoting Fungus

A study was conducted for endophytic antagonistic fungi obtained from the roots of healthy apple trees growing in nine replanted orchards in Shandong Province, China. The fungi were assessed for their ability to inhibit Fusarium proliferatum f. sp. malus domestica MR5, a fungal strain associated with apple replant disease (ARD). An effective endophyte, designated as strain 6S-2, was isolated and identified as Trichoderma asperellum. Strain 6S-2 demonstrated protease, amylase, cellulase, and laccase activities, which are important for the parasitic and antagonistic functions of pathogenic fungi. The inhibition rate of 6S-2 against Fusarium proliferatum f. sp. malus domestica MR5 was 52.41%. Strain 6S-2 also secreted iron carriers, auxin, ammonia and was able to solubilize phosphorus. Its fermentation extract and volatile substances inhibited the growth of MR5, causing its hyphae to twist, shrink, swell, and rupture. The antifungal activity of the 6S-2 fermentation extract increased with increasing concentrations. It promoted the production and elongation of Arabidopsis thaliana lateral roots, and the strongest effects were seen at a concentration of 50 mg/mL. A GC-MS analysis of the 6S-2 fermentation extract and volatile substances showed that they comprised mainly alkanes, alcohols, and furanones, as well as the specific volatile substance 6-PP. The application of 6S-2 spore suspension to replanted apple orchard soils reduced plant oxidative damage and promoted plant growth in a pot experiment. Therefore, the endophytic strain T. asperellum 6S-2 has the potential to serve as an effective biocontrol fungus for the prevention of ARD in China, and appears to promote plant growth.