The fungal biocontrol agent Coniothyrium minitans: production by solid-state fermentation, application and marketing

Microbial pesticides - challenges and future perspectives for testing and safety assessment with respect to human health

Plant protection measures are necessary to prevent pests and diseases from attacking and destroying crop plants and to meet consumer demands for agricultural produce. In the last decades the use of chemical pesticides has largely increased. Farmers are looking for alternatives. Biopesticides should be considered a sustainable solution. They may be less toxic than chemical pesticides, be very specific to the target pest, decompose quickly, and be less likely to cause resistance. On the other hand, lower efficacy and higher costs are two disadvantages of many biopesticides. Biopesticides include macroorganisms, natural compounds and microorganisms. Microbial pesticides are the most widely used and studied class of biopesticides. The greatest difference between microbial and chemical pesticides is the ability of the former to potentially multiply in the environment and on the crop plant after application. The data requirements for the European Union and the United States Environmental Protection Agency are highlighted, as these regulatory processes are the most followed in regions where local regulations for biopesticide products are not available or vague. New Approach Methods already proposed or harmonized for chemical pesticides are presented and discussed with respect to their use in evaluating microbial pesticide formulations. Evaluating the microbials themselves is not as simple as using the same validated New Approach Methods as for synthetic pesticides. Therefore, the authors suggest considering New Approach Method strategies specifically for microbials and global harmonization with acceptability with the advancements of such approaches. Further discussion is needed and greatly appreciated by the experts.

Botrytis cinerea type II inhibitor of apoptosis BcBIR1 enhances the biocontrol capacity of Coniothyrium minitans

Apoptosis-like programmed cell death is associated with fungal development, ageing, pathogenicity and stress responses. Here, to explore the potential of Botrytis cinerea type II inhibitor of apoptosis (IAP) BcBIR1 in elevating the biocontrol efficacy of Coniothyrium minitans, the BcBIR1 gene was heterologously expressed in C. minitans. Results indicated that the strains expressing BcBIR1 had higher rates of conidiation, mycelial growth and biomass growth than the wild-type strain. Moreover, BcBIR1 was found to inhibit apoptosis, indicating its role as an IAP in C. minitans. Under various abiotic stresses, the growth rates of BcBIR1-expressing strains were significantly higher than that of the wild-type strain. Moreover, the conidial survival rate of the BcBIR1-expressing strains treated with ultraviolet irradiation was enhanced. In antifungal activity assay, the culture filtrates of BcBIR1-expressing strains displayed a stronger inhibitory effect on B. cinerea and Sclerotinia sclerotiorum than the wild-type strain. The study also found that BcBIR1 expression increased the mycoparasitism against the sclerotia, but not the hyphae of S. sclerotiorum. Taken together, these results suggest that BcBIR1 enhances vegetative growth, conidiation, anti-apoptosis activity, abiotic stress resistance, antifungal activity and mycoparasitism in C. minitans. As an IAP, BcBIR1 may improve the control capacity of C. minitans against S. sclerotiorum.

Expression of a mycoparasite protease in plant petals suppresses the petal-mediated infection by necrotrophic pathogens

Sclerotinia sclerotiorum and Botrytis cinerea are necrotrophic plant-pathogenic fungi, causing substantial economic losses on many crops. So far, resistant cultivars against these pathogens are unavailable in most crops. Here, we show that the serine protease CmSp1 of Coniothyrium minitans, a well-characterized mycoparasite of S. sclerotiorum, contributed to suppressing the petal-mediated infection by S. sclerotiorum in rapeseed. Application of recombinant CmSp1 proteins facilitates the bulk degradation of S. sclerotiorum proteins and inhibits spore germination and hyphal growth of S. sclerotiorum and B. cinerea, thereby preventing the development of both diseases. Stable transgenic rapeseed plants with tissue-specific expression of CmSp1 in flower petals inhibit the petal-mediated infection by both S. sclerotiorum and B. cinerea, and resulting transgenic plants have no adverse effect on other agronomic traits. Thus, our findings provide a novel mechanism by which a mycoparasite inhibits fungal pathogens and an environmentally friendly disease management strategy.

The Registration Situation and Use of Mycopesticides in the World

Mycopesticides are living preparations that use fungal cells, such as spores and hyphae, as active ingredients. They mainly include mycoinsecticides, mycofungicides, mycoherbicides and nematophagous fungi. The utilization of fungi for controlling agricultural pests can be traced back to approximately 1880, when entomopathogenic fungi were initially employed for this purpose. However, it was not until 1965 that the world's first mycopesticide, Beauveria bassiana, was registered as Boverin® in the former Soviet Union. In past decades, numerous novel mycopesticides have been developed for their lower R&D costs, as well as the environmentally friendly and safe nature. In this review, we investigated the mycopesticides situation of registration in USA, EU, China, Canada and Australia. Superisingly, it was found that the registered mycopesticides are extremely raised in recent years. Currently, the insecticides, fungicides (nematocides) and herbicides were respectively registered 27, 53 and 8 fungal strains. This paper also analyzes the main problems currently faced by mycopesticides and offers suggestions for their future development.

Soil and Phytomicrobiome for Plant Disease Suppression and Management under Climate Change: A Review

The phytomicrobiome plays a crucial role in soil and ecosystem health, encompassing both beneficial members providing critical ecosystem goods and services and pathogens threatening food safety and security. The potential benefits of harnessing the power of the phytomicrobiome for plant disease suppression and management are indisputable and of interest in agriculture but also in forestry and landscaping. Indeed, plant diseases can be mitigated by in situ manipulations of resident microorganisms through agronomic practices (such as minimum tillage, crop rotation, cover cropping, organic mulching, etc.) as well as by applying microbial inoculants. However, numerous challenges, such as the lack of standardized methods for microbiome analysis and the difficulty in translating research findings into practical applications are at stake. Moreover, climate change is affecting the distribution, abundance, and virulence of many plant pathogens, while also altering the phytomicrobiome functioning, further compounding disease management strategies. Here, we will first review literature demonstrating how agricultural practices have been found effective in promoting soil health and enhancing disease suppressiveness and mitigation through a shift of the phytomicrobiome. Challenges and barriers to the identification and use of the phytomicrobiome for plant disease management will then be discussed before focusing on the potential impacts of climate change on the phytomicrobiome functioning and disease outcome.

Potential Biocontrol Agents of Corn Tar Spot Disease Isolated from Overwintered Phyllachora maydis Stromata

Tar spot disease in corn, caused by Phyllachora maydis, can reduce grain yield by limiting the total photosynthetic area in leaves. Stromata of P. maydis are long-term survival structures that can germinate and release spores in a gelatinous matrix in the spring, which are thought to serve as inoculum in newly planted fields. In this study, overwintered stromata in corn leaves were collected in Central Illinois, surface sterilized, and caged on water agar medium. Fungi and bacteria were collected from the surface of stromata that did not germinate and showed microbial growth. Twenty-two Alternaria isolates and three Cladosporium isolates were collected. Eighteen bacteria, most frequently Pseudomonas and Pantoea species, were also isolated. Spores of Alternaria, Cladosporium, and Gliocladium catenulatum (formulated as a commercial biofungicide) reduced the number of stromata that germinated compared to control untreated stromata. These data suggest that fungi collected from overwintered tar spot stromata can serve as biological control organisms against tar spot disease.

Solid-State Fermentation: Applications and Future Perspectives for Biostimulant and Biopesticides Production

With the expansion of the green products market and the worldwide policies and strategies directed toward a green revolution and ecological transition, the demand for innovative approaches is always on the rise. Among the sustainable agricultural approaches, microbial-based products are emerging over time as effective and feasible alternatives to agrochemicals. However, the production, formulation, and commercialization of some products can be challenging. Among the main challenges are the industrial production processes that ensure the quality of the product and its cost on the market. In the context of a circular economy, solid-state fermentation (SSF) might represent a smart approach to obtaining valuable products from waste and by-products. SSF enables the growth of various microorganisms on solid surfaces in the absence or near absence of free-flowing water. It is a valuable and practical method and is used in the food, pharmaceutical, energy, and chemical industries. Nevertheless, the application of this technology in the production of formulations useful in agriculture is still limited. This review summarizes the literature dealing with SSF agricultural applications and the future perspective of its use in sustainable agriculture. The survey showed good potential for SSF to produce biostimulants and biopesticides useful in agriculture.

Simultaneous lipase production and immobilization: morphology and physiology study of Penicillium simplicissimum in submerged and solid-state fermentation with polypropylene as an inert support

The influence of different carbon sources (glucose (G), olive oil (O), and a combination of both (GO)) in the physiology (biomass and lipase production) and morphology (light and environmental and scanning electron microscopy) of the fungus Penicillium simplicissimum by applying submerged (SmF) and solid-state (SSF) fermentations was investigated. The cultivation was carried out using polypropylene as hydrophobic inert support in SmF and SSF to understand better the influence of a support for the fungus growth and also provides the immobilization of lipases during its production. Micrographs show different morphologies: in SSF, the fungus grows on and inside the inert support independent of the media; in SmF, the formation of high-density spherical pellets obtained in medium GO leads to the best productivity and specific product yield Y_p/x._.Conidiation is observed mainly in SSF, a few in SmF with polypropylene as inert support and not in SmF, which may indicate a stress condition in SSF. Possibly, the morphology acquired by the fungus under stressful conditions may be the key to the higher biomass and lipase productivity at SSF. The developed process with simultaneous production and immobilization of lipase leads to a new promissory biocatalyst once it can be directly applied with no need for downstream processes.

Cloning and Molecular Characterization of CmOxdc3 Coding for Oxalate Decarboxylase in the Mycoparasite Coniothyrium minitans

Coniothyrium minitans (Cm) is a mycoparasitic fungus of Sclerotinia sclerotiorum (Ss), the causal agent of Sclerotinia stem rot of oilseed rape. Ss can produce oxalic acid (OA) as a phytotoxin, whereas Cm can degrade OA, thereby nullifying the toxic effect of OA. Two oxalate decarboxylase (OxDC)-coding genes, CmOxdc1 and CmOxdc2, were cloned, and only CmOxdc1 was found to be partially responsible for OA degradation, implying that other OA-degrading genes may exist in Cm. This study cloned a novel OxDC gene (CmOxdc3) in Cm and its OA-degrading function was characterized by disruption and complementation of CmOxdc3. Sequence analysis indicated that, unlike CmOxdc1, CmOxdc3 does not have the signal peptide sequence, implying that CmOxDC3 may have no secretory capability. Quantitative RT-PCR showed that CmOxdc3 was up-regulated in the presence of OA, malonic acid and hydrochloric acid. Deletion of CmOxdc3 resulted in reduced capability to parasitize sclerotia of Ss. The polypeptide (CmOxDC3) encoded by CmOxdc3 was localized in cytoplasm and gathered in vacuoles in response to the extracellular OA. Taken together, our results demonstrated that CmOxdc3 is a novel gene responsible for OA degradation, which may work in a synergistic manner with CmOxdc1.

Optimization of culture conditions for enhanced production of extracellular α-amylase using solid state and submerged fermentation from Aspergillus tamarii MTCC5152

Amylases are one of the main enzymes used in various industries such as food, fermentation, textile and pharmaceuticals. Microorganisms are the potent sources of amylase enzyme, apart from plant and animal sources. Fungal amylases are more stable than bacterial amylases. The production of extracellular α-amylase from Aspergillus tamarii MTCC5152 using solid state and submerged fermentation and the various nutritional factors influencing its production were studied. A higher activity of α-amylase (519.40 u/g) was attained in a medium having wheat bran alone as the substrate at an initial moisture content of 70% v/w with 2.5% v/w of inoculum level (containing 10⁶ spores/ml) after 4 days of incubation at 28°C by SSF. Addition of 1% glucose to wheat bran containing basal medium enhanced α-amylase production (6.49 u/ml) after 4 days of incubation by SmF method. Comparative evaluation of enzyme production by solid state and submerged fermentation methods produced better results in solid state fermentation method. This article is protected by copyright. All rights reserved.

Current developments in the resistance, quality, and production of entomopathogenic fungi

There is a worldwide concern to achieve food security with a sustainable approach, including the generation and implementation of techniques for the production of high-quality chemical-free crops. This food revolution has promoted the development and consolidation of programmes for integrated pest management. Some of those programmes include the use of diverse organisms (biological control agents) to suppress populations of pests potentially harmful to the crops. Among these biological control agents are entomopathogenic fungi that are highly effective in suppressing a diversity of insects and have, therefore, been produced and marketed throughout the world. However, the bottleneck for applying entomopathogenic fungi is the production of propagules (blastospores and conidia) with resistance to environment conditions and abiotic factors, maintaining high quality in terms of virulence. Therefore, this manuscript presents recent studies related to increasing resistance and quality using different bioreactors to produce conidia. The above presents a global panorama related to current developments that contribute to improving the resistance, quality, and production of entomopathogenic fungal propagules.

AMF Community Diversity Promotes Grapevine Growth Parameters under High Black Foot Disease Pressure

Black foot disease is one of the main grapevine root diseases observed worldwide and is especially problematic in New Zealand. Arbuscular mycorrhizal fungi (AMF) have been shown to reduce infection and mitigate the effect of black foot disease on grapevine rootstocks. In contrast to prior studies, which have limited their focus to the effect of one, two or a combination of only a small number of AMF species, this study used whole AMF communities identified from 101-14, 5C and Schwarzmann rootstocks sampled from New Zealand vineyards. The effect of AMF on black foot disease was investigated in a ‘home’ and ‘away’ experiment using three commercial grapevine rootstocks. The study produced some evidence that AMF treatments lowered disease incidence at 5 cm and disease severity in vines by 40% to 50% compared to the vines inoculated with the pathogen only. This work also showed that the presence of high disease incidence may have limited the potential disease protective effect of AMF community. However, despite the high disease incidence and severity, AMF inoculation increased vine growth parameters by 60% to 80% compared to the vines inoculated with the pathogen only. This study is the first to provide an understanding on how young grapevine rootstocks inoculated with their ‘home’ and ‘away’ AMF communities would respond to challenge with a black foot pathogen species mixture. Further research is required to understand the mechanistic effect of AMF colonization on the increase of grapevine growth parameters under high black foot disease pressure.

Variations in the Community Structure of Fungal Microbiota Associated with Apple Fruit Shaped by Fruit Bagging-Based Practice

The various fungal communities that adhere to apple fruit are influenced by agricultural practices. However, the effects of fruit bagging-based management practice on the fungal microbiota are still unknown, and little is known about the fungal communities of bagged apple fruit. We conducted a study using apple fruit grown in a conventionally managed orchard where pesticide use is an indispensable practice. Fungal communities were collected from the calyx-end and peel tissues of bagged and unbagged fruit and characterized using barcode-type next-generation sequencing. Fruit bagging had a stronger effect on fungal richness, abundance, and diversity of the fungal microbiota in comparison to non-bagging. In addition, bagging also impacted the compositional variation of the fungal communities inhabiting each fruit part. We observed that fruit bagging had a tendency to maintain ecological equilibrium since Ascomycota and Basidiomycota were more distributed in bagged fruit than in unbagged fruit. These fungal communities consist of beneficial fungi rather than potentially harmful fungi. Approximately 50 dominant taxa were detected in bagged fruit, for example, beneficial genera such as Articulospora, Bullera, Cryptococcus, Dioszegia, Erythrobasidium, and Sporobolomyces, as well as pathogenic genera such as Aureobasidium and Taphrina. These results suggested that fruit bagging could significantly increase fungal richness and promote healthy fungal communities, especially the harmless fungal communities, which might be helpful for protecting fruit from the effects of pathogens. This study provides a foundation for understanding the impacts of bagging-based practice on the associated fungal microbiota.

Tackling Control of a Cosmopolitan Phytopathogen: Sclerotinia

Phytopathogenic members of the Sclerotinia genus cause widespread disease across a broad range of economically important crops. In particular, Sclerotinia sclerotiorum is considered one of the most destructive and cosmopolitan of plant pathogens. Here, were review the epidemiology of the pathogen, its economic impact on agricultural production, and measures employed toward control of disease. We review the broad approaches required to tackle Sclerotinia diseases and include cultural practices, crop genetic resistance, chemical fungicides, and biological controls. We highlight the benefits and drawbacks of each approach along with recent advances within these controls and future strategies.

Genome-Wide Identification and Expression Analysis of the bZIP Transcription Factors in the Mycoparasite Coniothyrium minitans

The basic leucine zipper (bZIP) proteins family is one of the largest and most diverse transcription factors, widely distributed in eukaryotes. However, no information is available regarding the bZIP gene family in Coniothyrium minitans, an important biocontrol agent of the plant pathogen Sclerotinia sclerotiorum. In this study, we identified 34 bZIP genes from the C. minitans genome, which were classified into 8 groups based on their phylogenetic relationships. Intron analysis showed that 28 CmbZIP genes harbored a variable number of introns, and 15 of them shared a feature that intron inserted into the bZIP domain. The intron position in bZIP domain was highly conserved, which was related to recognize the arginine (R) and could be treated as a genomic imprinting. Expression analysis of the CmbZIP genes in response to abiotic stresses indicated that they might play distinct roles in abiotic stress responses. Results showed that 22 CmbZIP genes were upregulated during the later stage of conidial development. Furthermore, transcriptome analysis indicated that CmbZIP genes are involved in different stages of mycoparasitism. Among deletion mutants of four CmbZIPs (CmbZIP07, -09, -13, and -16), only ΔCmbZIP16 mutants significantly reduced its tolerance to the oxidative stress. The other mutants exhibited no significant effects on colony morphology, mycelial growth, conidiation, and mycoparasitism. Taken together, our results suggested that CmbZIP genes play important roles in the abiotic stress responses, conidial development, and mycoparasitism. These results provide comprehensive information of the CmbZIP gene family and lay the foundation for further research on the bZIP gene family regarding their biological functions and evolutionary history.

CmAim24 Is Essential for Mitochondrial Morphology, Conidiogenesis, and Mycoparasitism in Coniothyrium minitans

Coniothyrium minitans is an important mycoparasite of the notorious phytopathogenic fungus Sclerotinia sclerotiorum The mycoparasitism system of C. minitans-S. sclerotiorum is unique and important in probing fungi and fungal interactions. Here, we report a conidiation-deficient mutant, ZS-1TN1961, which was screened from a transfer DNA (T-DNA) insertional library of C. minitans A single-copy gene, encoding a protein with high sequence similarity to Aim24 (altered inheritance of mitochondria protein 24) in Saccharomyces cerevisiae, was disrupted by T-DNA insertion in this mutant. Gene replacement and complementation experiments confirmed that mutants lacking CmAim24 exhibited significantly reduced conidial production and germination as well as reduced sclerotial mycoparasitic ability. Furthermore, cellular localization assays showed that CmAim24 localized to mitochondria, and abnormal mitochondria were observed in the ΔCmAim24 mutant. The ΔCmAim24 mutant exhibited significant accumulation of reactive oxygen species (ROS) and a reduced ATP content in mycelia. In summary, our results suggest that CmAim24 plays a key role in mitochondrial architecture and function, conidiogenesis, and mycoparasitism in C. minitans IMPORTANCE Aim24 proteins are involved in mitochondrial biogenesis and accumulate between the two membranes of a mitochondrion. Their function in prokaryotes and filamentous fungi is as yet unknown. In the present study, we characterized an Aim24 protein, CmAim24, in the mycoparasite Coniothyrium minitans and proved its critical role in mitochondrial morphology and function, conidiogenesis, conidial germination, and mycoparasitism to S. sclerotiorum.

Comparison of pinoresinol diglucoside production by Phomopsis sp. XP-8 in different media and the characterisation and product profiles of the cultivation in mung bean

BACKGROUND

Phomopsis sp. XP-8 is an endophytic fungus with the ability to produce pinoresinol diglucoside (PDG) in vitro and thus has potential application in biosynthesis of PDG independent of plants. In order to enhance the production of PDG, 18 different natural materials were tested in solid-state cultivation of Phomopsis sp. XP-8.

RESULTS

Most of the tested natural materials promoted the production of PDG. A supplement derived from mung beans produced the highest PDG yield and better fungal growth than the other materials. Also, pinoresinol monoglucoside, pinoresinol and other substrates (phenylalanine, p-coumaric acid, cinnamic acid, caffeic acid, and ferulic acid) were obtained after fermentation on mung beans. Furthermore, PDG production was much higher when mung beans were incorporated into solid state agar versus a liquid medium. The highest pinoresinol diglucoside production (72.1 mg kg(-1) in fresh culture) was obtained in 9 days using a solid state culture of Phomopsis sp. XP-8 on a mung bean grain medium containing 100 g kg(-1) glucose. Mung bean water-soluble polysaccharide was identified as a major promoter of PDG production by Phomopsis sp. XP-8.

CONCLUSION

Mung bean, especially its water-soluble polysaccharide fraction, was an efficient natural material to promote PDG production by Phomopsis sp. XP-8. © 2015 Society of Chemical Industry.

Relationship between mycoparasites lifestyles and biocontrol behaviors against Fusarium spp. and mycotoxins production

Global food security research is seeking eco-friendly solutions to control mycotoxins in grain infected by fungi (molds). In particular, mycotoxigenic Fusarium spp. outbreak is a chronic threat for cereal grain production, human, and animal health. In this review paper, we discuss up-to-date biological control strategies in applying mycoparasites as biological control agents (BCA) to prevent plant diseases in crops and mycotoxins in grain, food, and feed. The aim is to increase food safety and to minimize economic losses due to the reduced grain yield and quality. However, recent papers indicate that the study of the BCA specialists with biotrophic lifestyle lags behind our understanding of the BCA generalists with necrotrophic lifestyle. We examine critical behavioral traits of the two BCA groups of mycoparasites. The goal is to highlight their major characteristics in the context of future research towards an efficient biocontrol strategy against mycotoxin-producing Fusarium species. The emphasis is put on biocontrol of Fusarium graminearum, F. avenaceum, and F. culmorum causing Fusarium head blight (FHB) in cereals and their mycotoxins.

Elucidating the Diversity of Aquatic Microdochium and Trichoderma Species and Their Activity against the Fish Pathogen Saprolegnia diclina

Animals and plants are increasingly threatened by emerging fungal and oomycete diseases. Amongst oomycetes, Saprolegnia species cause population declines in aquatic animals, especially fish and amphibians, resulting in significant perturbation in biodiversity, ecological balance and food security. Due to the prohibition of several chemical control agents, novel sustainable measures are required to control Saprolegnia infections in aquaculture. Previously, fungal community analysis by terminal restriction fragment length polymorphism (T-RFLP) revealed that the Ascomycota, specifically the genus Microdochium, was an abundant fungal phylum associated with salmon eggs from a commercial fish farm. Here, phylogenetic analyses showed that most fungal isolates obtained from salmon eggs were closely related to Microdochium lycopodinum/Microdochium phragmitis and Trichoderma viride species. Phylogenetic and quantitative PCR analyses showed both a quantitative and qualitative difference in Trichoderma population between diseased and healthy salmon eggs, which was not the case for the Microdochium population. In vitro antagonistic activity of the fungi against Saprolegnia diclina was isolate-dependent; for most Trichoderma isolates, the typical mycoparasitic coiling around and/or formation of papilla-like structures on S. diclina hyphae were observed. These results suggest that among the fungal community associated with salmon eggs, Trichoderma species may play a role in Saprolegnia suppression in aquaculture.

Solid phase bio-electrofermentation of food waste to harvest value-added products associated with waste remediation

A novel solid state bio-electrofermentation system (SBES), which can function on the self-driven bioelectrogenic activity was designed and fabricated in the laboratory. SBES was operated with food waste as substrate and evaluated for simultaneous production of electrofuels viz., bioelectricity, biohydrogen (H2) and bioethanol. The system illustrated maximum open circuit voltage and power density of 443 mV and 162.4 mW/m(2), respectively on 9 th day of operation while higher H2 production rate (21.9 ml/h) was observed on 19th day of operation. SBES system also documented 4.85% w/v bioethanol production on 20th day of operation. The analysis of end products confirmed that H2 production could be generally attributed to a mixed acetate/butyrate-type of fermentation. Nevertheless, the presence of additional metabolites in SBES, including formate, lactate, propionate and ethanol, also suggested that other metabolic pathways were active during the process, lowering the conversion of substrate into H2. SBES also documented 72% substrate (COD) removal efficiency along with value added product generation. Continuous evolution of volatile fatty acids as intermediary metabolites resulted in pH drop and depicted its negative influence on SBES performance. Bio-electrocatalytic analysis was carried out to evaluate the redox catalytic capabilities of the biocatalyst. Experimental data illustrated that solid-state fermentation can be effectively integrated in SBES for the production of value added products with the possibility of simultaneous solid waste remediation.

CmpacC regulates mycoparasitism, oxalate degradation and antifungal activity in the mycoparasitic fungus Coniothyrium minitans

The PacC/Rim101 pH-responsive transcription factor is an important pathogenicity element for many plant-pathogenic fungi. In this study, we investigated the roles of a PacC homologue, CmpacC, in the mycoparasitic fungus Coniothyrium minitans. CmpacC was confirmed to have the transcriptional activation activity by the transcriptional activation test in Saccharomyces cerevisiae. Disruption of CmpacC resulted in impaired fungal responses to ambient pH. Compared to the wild-type, the CmpacC-disruption mutant ΔCmpacC-29 was significantly suppressed for activities of chitinase and β-1,3-glucanase at pH 5 and 7, consistent with reduced expression levels of Cmch1 and Cmg1 coding for the two enzymes respectively. However, the mutant displayed acidity-mimicking phenotypes such as improved oxalate degradation and increased antifungal activity at pH 6 or higher. Improved efficacy in oxalate degradation by ΔCmpacC-29 was consistent with the enhanced expression level of Cmoxdc1 coding for oxalate decarboxylase. CmpacC transcriptional activation of Cmch1 and Cmg1 and repression of Cmoxdc1 were verified by the presence of the PacC/Rim101 consensus binding-motifs in gene promoter regions and by the promoter DNA-binding assays. This study suggests that CmpacC plays an activator role in regulation of C. minitans mycoparasitism, whereas plays a repressor role in regulation of oxalate degradation and possibly antifungal activity of C. minitans.

The plant microbiome at work

Plants host distinct microbial communities on and inside their tissues designated the plant microbiota. Microbial community profiling enabled the description of the phylogenetic structure of the plant microbiota to an unprecedented depth, whereas functional insights are largely derived from experiments using individual microorganisms. The binary interplay between isolated members of the plant microbiota and host plants ranges from mutualistic to commensalistic and pathogenic relationships. However, how entire microbial communities capable of executing both growth-promoting and growth-compromising activities interfere with plant fitness remains largely unknown. Ultimately, unravelling the net result of microbial activities encoded in the extended plant genome-the plant microbiome-will be key to understanding and exploiting the full yield potential of a crop plant. In this perspective, we summarize first achievements of plant-microbiome research, we discuss future research directions, and we provide ideas for the translation of basic science to application to capitalize on the plant microbiome at work.

Microbial consortium-mediated reprogramming of defence network in pea to enhance tolerance against Sclerotinia sclerotiorum

AIMS

To evaluate the potentiality of three rhizosphere microorganisms in suppression of Sclerotinia rot in pea in consortia mode and their impact on host defence responses.

METHODS AND RESULTS

Pseudomonas aeruginosa PJHU15, Trichoderma harzianum TNHU27 and Bacillus subtilis BHHU100 from rhizospheric soils were selected based on compatibility, antagonistic and plant growth promotion activities. The microbes were used as consortia to assess their ability to trigger the phenylpropanoid and antioxidant activities and accumulation of proline, total phenol and pathogenesis-related (PR) proteins in pea under the challenge of the soft-rot pathogen Sclerotinia sclerotiorum. The triple-microbe consortium and single-microbe treatments showed 1·4-2·3 and 1·1-1·7-fold increment in defence parameters, respectively, when compared to untreated challenged control. Activation of the phenylpropanoid pathway and accumulation of total phenolics were highest at 48h, whereas accumulation of proline and PR proteins along with activities of the antioxidant enzymes was highest at 72h.

CONCLUSIONS

The compatible microbial consortia triggered defence responses in an enhanced level in pea than the microbes alone and provided better protection against Sclerotinia rot.

SIGNIFICANCE AND IMPACT OF THE STUDY

  Rhizosphere microbes in consortium can enhance protection in pea against the soft-rot pathogen through augmented elicitation of host defence responses.

Formulations of the endophytic bacterium Bacillus subtilis Tu-100 suppress Sclerotinia sclerotiorum on oilseed rape and improve plant vigor in field trials conducted at separate locations

Sclerotinia sclerotiorum causes serious yield losses in crops in the People's Republic of China. Two formulations of oilseed rape seed containing the bacterium Bacillus subtilis Tu-100 were evaluated for suppression of this pathogen in field trials conducted at two independent locations. The pellet formulation significantly reduced disease (incidence and disease index) and increased plant dry mass, while the wrap formulation significantly reduced disease incidence and significantly increased plant dry mass at both field locations. Mean seed yield per 120 plants with both formulations of isolate Tu-100 was significantly greater than the appropriate controls, but at only one of the locations. Both formulations provided stable B. subtilis Tu-100 biomass (≥10(5) CFU·g(-1)) and seed germination (≥85%) over a 6 month period at room temperature. Polymerase chain reaction and DNA sequence analysis identified ituC and ituD, and bacAB and bacD in the genome of isolate Tu-100. These genes are involved in the biosynthesis of iturin and bacilysin. Iturin was detected in culture filtrates from isolate Tu-100, with thin layer chromatography. Detection of bacilysin was not attempted. Experiments reported here indicate the commercial viability of B. subtilis Tu-100 for suppression of S. sclerotiorum on oilseed rape.

Phosphoribosylamidotransferase, the first enzyme for purine de novo synthesis, is required for conidiation in the sclerotial mycoparasite Coniothyrium minitans

Coniothyrium minitans is an important sclerotial parasite of the fungal phytopathogen, Sclerotinia sclerotiorum. Previously, we constructed a T-DNA insertional library, and screened for many conidiation-deficient mutants from this library. Here, we report a T-DNA insertional mutant ZS-1T21882 that completely lost conidiation. In mutant ZS-1T21882, the T-DNA was integrated into a gene (CmPrat-1) which encodes phosphoribosylamidotransferase (PRAT, EC 2.4.2.14), an enzyme catalyzing the first committed step in de novo purine nucleotide synthesis. Gene replacement and complementation experiments confirmed that phosphoribosylamidotransferase is essential for conidiation of C. minitans. Mutant ZS-1T21882 did not grow on modified Czapek-Dox broth (MCD), but it grew well on MCD amended with IMP or AMP. The conidial production of this mutant was dependent on the dosage of IMP amended. At low concentrations, such as 0.1 mM and 0.25 mM, the mutant produced very few pycnidia, while up to 0.75 mM or higher, the conidiation of this mutant was restored completely. cAMP could not restore the conidiation of mutant ZS-1T21882 when amended into MCD, but could when amended into PDA. Neither GMP nor cGMP could restore the conidiation in MCD or in PDA. Our findings suggest that phosphoribosylamidotransferase is essential for conidiation of C. minitans via adenosine related molecules. Furthermore, when dual cultured with its host, this mutant produced conidia in the host mycelium and on the sclerotia of S. sclerotiorum, but not in dead mycelium or on dead sclerotia, suggesting that C. minitans is likely to able to obtain adenosine or related components from its host during parasitization.

Solid phase microbial fuel cell (SMFC) for harnessing bioelectricity from composite food waste fermentation: influence of electrode assembly and buffering capacity

Solid phase microbial fuel cells (SMFC; graphite electrodes; open-air cathode) were designed to evaluate the potential of bioelectricity production by stabilizing composite canteen based food waste. The performance was evaluated with three variable electrode-membrane assemblies. Experimental data depicted feasibility of bioelectricity generation from solid state fermentation of food waste. Distance between the electrodes and presence of proton exchange membrane (PEM) showed significant influence on the power yields. SMFC-B (anode placed 5 cm from cathode-PEM) depicted good power output (463 mV; 170.81 mW/m(2)) followed by SMFC-C (anode placed 5 cm from cathode; without PEM; 398 mV; 53.41 mW/m(2)). SMFC-A (PEM sandwiched between electrodes) recorded lowest performance (258 mV; 41.8 mW/m(2)). Sodium carbonate amendment documented marked improvement in power yields due to improvement in the system buffering capacity. SMFCs operation also documented good substrate degradation (COD, 76%) along with bio-ethanol production. The operation of SMFC mimicked solid-sate fermentation which might lead to sustainable solid waste management practices.

Characterization of some culture factors affecting oxalate degradation by the mycoparasite Coniothyrium minitans

AIMS

To find possible approaches to utilize the mechanism of oxalate degradation by Coniothyrium minitans (Cm) in controlling the plant pathogen Sclerotinia sclerotiorum (Ss).

METHODS AND RESULTS

Differences in oxalate degradation by different Cm strains and effects of the initial oxalate concentration, ambient pH and nutrient factors on mycelial growth and oxalate degradation by Cm were studied in shaken cultures. Results showed that two wild-type Cm strains, Chy-1 and ZS-1, did not differ in oxalate degradation in modified potato dextrose broth (mPDB) amended with oxalic acid (OA). Cm could grow in mPDB amended with sodium oxalate (SO-mPDB) at pH 6.5 or with ammonium oxalate (AO-PDB) at pH 6.2, but oxalate degradation was very low; oxalate degradation was greatly enhanced in SO- or AO-mPDB with pH being lowered to 2.8-2.9. Similarly, oxalate degradation was higher than 90% in OA-amended mPDB at pH 4.4 but was reduced to be <22% at pH 7.0. Five carbon sources and three nitrogen sources investigated and nutrients from mycelia and sclerotia of Ss were favorable for the growth of Cm and OA degradation by Cm.

CONCLUSIONS

Cm can degrade oxalate under acidic pH. Exudates from mycelia or sclerotia of Ss may serve as nutrients for Cm mycelial growth and degradation of oxalate secreted by Ss.

SIGNIFICANCE AND IMPACT OF THE STUDY

The finding of oxalate degradation laid a foundation for mining-related genes in Cm for engineering plant resistance against Ss. Elucidation of the importance of acidic pH and nutrients from Ss in oxalate degradation by Cm will help to understand the interaction between Cm and Ss.

Potential of biofilm-based biofuel production

Biofilm technology has been extensively applied to wastewater treatment, but its potential application in biofuel production has not been explored. Current technologies of converting lignocellulose materials to biofuel are hampered by costly processing steps in pretreatment, saccharification, and product recovery. Biofilms may have a potential to improve efficiency of these processes. Advantages of biofilms include concentration of cell-associated hydrolytic enzymes at the biofilm-substrate interface to increase reaction rates, a layered microbial structure in which multiple species may sequentially convert complex substrates and coferment hexose and pentose as hydrolysates diffuse outward, and the possibility of fungal-bacterial symbioses that allow simultaneous delignification and saccharification. More importantly, the confined microenvironment within a biofilm selectively rewards cells with better phenotypes conferred from intercellular gene or signal exchange, a process which is absent in suspended cultures. The immobilized property of biofilm, especially when affixed to a membrane, simplifies the separation of biofuel from its producer and promotes retention of biomass for continued reaction in the fermenter. Highly consolidated bioprocessing, including delignification, saccharification, fermentation, and separation in a single reactor, may be possible through the application of biofilm technology. To date, solid-state fermentation is the only biofuel process to which the advantages of biofilms have been applied, even though it has received limited attention and improvements. The transfer of biofilm technology from environmental engineering has the potential to spur great innovations in the optimization of biofuel production.

In vitro and in vivo antagonism of actinomycetes isolated from Moroccan rhizospherical soils against Sclerotium rolfsii: a causal agent of root rot on sugar beet (Beta vulgaris L.)

AIMS

To evaluate the ability of the isolated actinomycetes to inhibit in vitro plant pathogenic fungi and the efficacy of promising antagonistic isolates to reduce in vivo the incidence of root rot induced by Sclerotium rolfsii on sugar beet.

METHODS AND RESULTS

Actinomycetes isolated from rhizosphere soil of sugar beet were screened for antagonistic activity against a number of plant pathogens, including S. rolfsii. Ten actinomycetes out of 195 screened in vitro were strongly inhibitory to S. rolfsii. These isolates were subsequently tested for their ability to inhibit sclerotial germination and hyphal growth of S. roflsii. The most important inhibitions were obtained by the culture filtrate from the isolates J-2 and B-11, including 100% inhibition of sclerotial germination and 80% inhibition of hyphal growth. These two isolates (J-2 and B-11) were then screened for their ability to protect sugar beet against infection of S. rolfsii induced root rot in a pot trial. The treatment of S. rolfsii infested soil with a biomass and culture filtrate mixture of the selected antagonists reduced significantly (P < or = 0.05) the incidence of root rot on sugar beet. Isolate J-2 was most effective and allowed a high fresh weight of sugar beet roots to be obtained. Both antagonists J-2 and B-11 were classified as belonging to the genus Streptomyces species through morphological and chemical characteristics as well as 16S rDNA analysis.

CONCLUSION

Streptomyces isolates J-2 and B-11 showed a potential for controlling root rot on sugar beet and could be useful in integrated control against diverse soil borne plant pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

This investigation showed the role, which actinomycete bacteria can play to control root rot caused by S. rolfsii, in the objective to reduce treatments with chemical fungicides.

Selection of endophytic fungi from comfrey (Symphytum officinale L.) for in vitro biological control of the phytopathogen Sclerotinia sclerotiorum (Lib.)

Biological control consists of using one organism to attack another that may cause economic damage to crops. Integrated Pest Management (IPM) is a very common strategy. The white mold produced by Sclerotinia sclerotiorum (Lib.) causes considerable damage to bean crops. This fungus is a soil inhabitant, the symptoms of which are characterized by water-soaked lesions covered by a white cottony fungal growth on the soil surface and/or the host plant. Possible biological control agents taken from plants are being investigated as phytopathogen inhibitors. These are endophytic microorganisms that inhabit the intercellular spaces of vegetal tissues and are often responsible for antimicrobial production. The objective of the present study was to select endophytic fungi isolated from comfrey (Symphytum officinale L.) leaves with in vitro antagonist potential against the phytopathogenic fungus S. sclerotiorum. Twelve isolates of endophytic fungi and a pathogenic strain of S. sclerotiorum were used in the challenge method. With the aid of this method, four endophytes with the best antagonistic activity against S. sclerotiorum were selected. Pathogen growth inhibition zones were considered indicative of antibiosis. The percentages of pathogenic mycelia growth were measured both with and without the antagonist, resulting in growth reductions of 46.7% to 50.0% for S. sclerotiorum. These analyses were performed by evaluating the endophytic/pathogenic mycelia growth in mm/day over an eight-day period of antagonistic tests.

Utilization of winery wastes for Trichoderma viride biocontrol agent production by solid state fermentation

Biocontrol agents are safe and environmental friendly alternatives for pesticides in agriculture application. Trichoderma viride WEBL0703 performed a high level of antagonistic activity toward a broad spectrum of phytopathogens and was determined as a biocontrol agent, which was produced by solid state fermentation using grape marc and wine lees. The maximum yield of T. viride conidia was up to 6.65 x 10(9) CFU/g initial dry substrate (IDS) after 10 d fermentation. As important enzymes for protecting plants from disease, chitinase, beta-glucanase, and pectinase yields were 47.8 U/g IDS, 8.32 U/g IDS and 9.83 U/g IDS, respectively. These results show that it is feasible to convert winery wastes to a value-added and environmental friendly biocontrol agent.

Coprinellus curtus(Hitoyo-take) prevents diseases of vegetables caused by pathogenic fungi

A strain of Coprinellus curtus (designated GM-21), a basidiomycete that suppressed bottom-rot disease of Chinese cabbage, 'pak-choi' (Brassica campestris), caused by the pathogen Rhizoctonia solani Pak-choi 2 was isolated. The mechanism of plant disease suppression was discovered to be hyphal interference, a combative fungal interaction between strain GM-21 and the pathogen. The antifungal spectrum of strain GM-21 was shown to include R. solani and Fusarium sp., i.e. strain GM-21 showed disease-suppressive ability against bottom-rot disease of lettuce and Rhizoctonia-patch disease of mascarene grass caused by strains of R. solani. In addition, clear evidence of hyphal interference between strain GM-21 and Fusarium pathogens that cause crown (foot) and root-rot disease of tomato and Fusarium wilt of melon, respectively, was demonstrated. It was thus considered that GM-21 is effective for suppressing soil-borne pathogens, and that GM-21 presents new possibilities for biological control of vegetable diseases.

Microbial competition, lack in macronutrients, and acidity as main obstacles to the transfer of basidiomycetous ground fungi into (organically or heavy-metal contaminated) soils

Non-symbiotic soil microorganisms which have been expensively engineered or selected to support plant nutrition, control root diseases, degrade xenobiotic hydrocarbons, and repress or stimulate heavy metal uptake of plants fail to survive in target soils. This prompted studies into the role of chemistry and microbial pre-colonization of 23 top soils in long-term growth of basidiomycetes. Fungi are seen as auxiliary agents in soil remediation. Untreated soils (1.5 L) were colonized by lignocellulose preferring ground fungi such as Agaricus aestivalis, A. bisporus, A. campestris, A. edulis, A. macrocarpus, A. porphyrizon, Agrocybe dura, A. praecox, Clitocybe sp., Coprinus comatus, Lepista nuda, L. sordida, Macrolepiota excoriata, M. procera, Stropharia coronilla, and S. rugoso-annulata. Spawn mycelia of fairy-ring-type fungi such as Agaricus arvensis, A. fissuratus, A. langei, A. lanipes, A. pilatianus, Lyophyllum sp., and Marasmius oreades died back in contact with non-sterile soils. Fungal growth correlated positively with the soils' Ct Ca K Mg content and negatively with microbial CO2 evolution. Pasteurization and autoclaving increased mycelial growth and life span in soils pH 6.6-8.2. Growth of pH-sensitive but not of pH-tolerant fungi was inhibited on the Ca-deficient soils pH 4-4.4 (-5.6) and was not improved by autoclaving. The pretended fungistasis of acid soils to pH-sensitive fungi was controlled by N P K mineral (pH not altering) or organic (pH increasing) fertilizing as well as by neutralization with NaOH or CaCO3. Although microbial competition was mortal to 33% of the fungal mycelia inserted into natural unplanted soils, further seriously antifungal effects beyond those pretended by low pH conditions and shortage in mineral macronutrients were not identified.

Modeling conversion and transport phenomena in solid-state fermentation: A review and perspectives

Solid-state fermentation (SSF) is accompanied inevitably by development of concentration and temperature gradients within the substrate particles and microbial biofilms. These gradients are needed for driving the transport of substrates and products. In addition, concentration gradients have been suggested to be crucial for obtaining the characteristics that define the products of SSF; nevertheless, gradients are also known to result in reduced productivity and unwanted side reactions. Solid-state fermentations are generally batch processes and this further complicates their understanding as conditions change with time. Mathematical models are therefore needed for improving the understanding of SSF processes and allowing their manipulation to achieve the desired outcomes. Existing models of SSF processes describe coupled substrate conversion and diffusion and the consequent microbial growth. Existing models disregard many of the significant phenomena that are known to influence SSF. As a result, available models cannot explain the generation of the numerous products that form during any SSF process and the outcome of the process in terms of the characteristics of the final product. This review critically evaluates the proposed models and their experimental validation. In addition, important issues that need to be resolved for improved modeling of SSF are discussed.

Decreased incidence of disease caused by Sclerotinia sclerotiorum and improved plant vigor of oilseed rape with Bacillus subtilis Tu-100

Sclerotinia sclerotiorum causes serious yield losses in oilseed crops worldwide. Bacillus subtilis Tu-100 significantly reduced (P< or =0.05) the incidence of disease caused by S. sclerotiorum on oilseed rape at harvest in two trials conducted in fields artificially infested with this pathogen. Mean plant dry weight was significantly greater (P< or =0.05) and mean plant length was significantly greater (P< or =0.07) at the seven-true-leaf stage with the Tu-100 treatment than with the control. Mean seed yield per 120 plants at harvest was significantly greater (P< or =0.05) in the second field trial with treatments containing isolate Tu-100. B. subtilis Tu-100 also promoted the growth of hydroponically grown oilseed rape. Plants were approximately 15% greater in dry weight (P< or =0.0001) and 6% greater in length (P< or =0.0025) when grown in the presence of isolate Tu-100 in Hoagland's solution, compared with the noninoculated control. In gnotobiotic studies, the lacZ-tagged strain B. subtilis Tu-100(pUC18) was detected within all roots of oilseed rape. Isolate Tu-100 did not persist in the ectorhizosphere of oilseed rape. Populations of this isolate decreased from 8.5x10(8) colony-forming units (CFU) per seed to approximately 10(2) CFU in the plant ectorhizosphere within 30 days of sowing in autoclaved soil.

Transformation of Coniothyrium minitans, a parasite of Sclerotinia sclerotiorum, with Agrobacterium tumefaciens

Coniothyrium minitans is a potential biological control agent of the plant pathogenic fungus Sclerotinia sclerotiorum. In this research, T-DNA insertional transformation of strain ZS-1 of C. minitans mediated by Agrobacterium tumefaciens was obtained, with optimization of spore maturity for transformation. After confirmation by PCR, transformants were subjected to Southern blot analysis, and results showed that more than 82.7% of transformants had single T-DNA insertions, and 12.1% of transformants had two copies T-DNA insertions. The genomic DNA segments of transformants flanking the T-DNA could be amplified from both borders with TAIL-PCR. Four types of mutants were screened and identified from the T-DNA insertional library, which comprised sporulation deficient mutants, pathogenicity deficient mutants, pigment change mutants and antibiotic deficient mutant, and some of the mutants were described; the number and frequency of each type of mutant from the library were calculated, and the frequency of each type is 3.27 x 10(-3), 1.0 x 10(-4), 1.4 x 10(-4), 2.5 x 10(-4), respectively. The successful creation of the T-DNA insertional transformation library may help us to unravel the interaction between a parasite and its host at a molecular level, to clarify the differentiation and development of this fungus, and to analyze and clone functional genes from the biocontrol microorganism in tripartite associations.

Effect of low oxygen concentrations on growth and α-amylase production of Aspergillus oryzae in model solid-state fermentation systems

Oxygen transfer in the fungal mat is a major concern in solid-state fermentation (SSF). Oxygen supply into the mycelial layers is hampered by diffusion limitation. For aerobic fungi, like Aspergillus oryzae, this oxygen depletion can be a severely limiting factor for growth and metabolite production. This paper describes the effects of a low oxygen concentration on growth at the levels of individual hyphae, colonies and overcultures, and on alpha-amylase production in overcultures. PDA medium was used to study the effect of a low oxygen concentration on hyphal elongation rate and branching frequency of hyphae, and radial extension rate of colonies of A. oryzae. We found similar saturation constants (K(O2)) of 0.1% (v/v in the gas phase) for oxygen concentration described with Monod kinetics, for branching frequency of hyphae and colony extension rate. When A. oryzae was grown as an over-culture on wheat-flour model substrate at 0.25% (v/v) oxygen concentration, the reduction in growth was more pronounced than as individual hyphae and a colony on PDA medium. Experimental results also showed that the specific alpha-amylase production rate under the condition of 0.25% (v/v) oxygen was reduced. Because the value of K(O2) is relatively low, it is reasonable to simplify the kinetics of growth of A. oryzae to zero-order kinetics in coupled diffusion/reaction models.

Production, survival and efficacy of Coniothyrium minitans conidia produced in shaken liquid culture

Coniothyrium minitans is a fungal biocontrol agent of the plant pathogen Sclerotinia sclerotiorum. Growth and sporulation of 21 strains of C. minitans were examined on potato dextrose agar (PDA) and compared with that in potato dextrose broth (PDB) in shaken culture after 12 days at 20 degrees C, to identify strains with potential for inoculum production in liquid culture. Four strains that produced high numbers of pycnidia in PDA also formed pycnidia on mycelial strands in PDB and 10(7) conidia ml(-1) broth were produced. The other strains formed pellets during shaking, resulting in production of less than 10(5) conidia ml(-1). Conidia from shaken PDB culture had the same ability to infect and rot sclerotia of S. sclerotiorum as conidia produced routinely on PDA, and survived well in dry kaolin dust for 6 months at temperatures less than 8 degrees C with less than 1 log(10) colony forming units mg(-1) loss. These results suggest that it might be possible to identify useful strains of C. minitans for future commercial conidial production in liquid fermentation systems based on morphological characteristics on agar.