Fungal wars: The underlying molecular repertoires of combating mycelia

Fused expression of Sm1-Chit42 proteins for synergistic mycoparasitic response of Trichoderma afroharzianum on Botrytis cinerea

Sm1 and Chit42 of Trichoderma have been universally confirmed as crucial biocontrol factors against pathogen infection through induced resistance and mycoparasitism, respectively. However, not enough work has been conducted to understand the novel function of fused expression of these two proteins in Trichoderma. The results of this study demonstrated that Sm1-Chit42 protein (SCf) engineered T. afroharzianum strain OE:SCf exerted synergistic inhibition to Botrytis cinerea growth at multiple stages of mycoparasitic interaction of T. afroharzianum and B. cinerea including chemotropism sensing, hyphal coiling, hydrophobicity modulation, cell wall adhesion, virulence reduction and pathogen killing by ROS. These results highlight a novel mycoparasitic system in Trichoderma strains engineered with Sm1-Chit42 chimeric protein to combat B. cinerea growth and reproduction, which would lay a strong foundation for exploring a new engineered Trichoderma biofungicide created with chimeric proteins in the future.

Fungal-fungal and fungal-bacterial interactions in aquatic decomposer communities: bacteria promote fungal diversity

Fungi produce a variety of extracellular enzymes making recalcitrant substrates bioavailable. Thus, fungi are central for decomposition of dead organic matter such as leaf litter. Despite their ecological importance, our understanding of relationships between fungal species diversity and ecosystem functioning is limited, especially with regard to aquatic habitats. Moreover, fungal interactions with other groups of microorganisms such as bacteria are rarely investigated. This lack of information may be attributed to methodological limitations in tracking the biomass of individual fungal species in communities, impeding a detailed assessment of deviations from the overall performance expected from the sum of individual species' performances, so-called net diversity effects (NDEs). We used fungal species-specific biomolecular tools to target fungal-fungal and fungal-bacterial interactions on submerged leaves using four cosmopolitan aquatic fungal species and a stream microbial community dominated by bacteria. In microcosms, we experimentally manipulated fungal diversity and bacterial absence/presence and assessed functional performances and fungal community composition after 14 days of incubation. Fungal community data was used to evaluate NDEs on leaf colonization. The individual fungal species were functionally distinct and fungal cultures were on average more efficient than the bacterial culture. In absence of bacteria, NDEs correlated with growth rate (negatively) and genetic divergence (positively), but were predominantly negative, suggesting that higher fungal diversity led to a lower colonization success (niche overlap). In both absence and presence of bacteria, the overall functional performances of the communities were largely defined by their composition (i.e., no interactions at the functional level). In presence of bacteria, NDEs correlated with genetic divergence (positively) and were largely positive, suggesting higher fungal diversity stimulated colonization (niche complementarity). This stimulation may be driven by a bacteria-induced inhibition of fungal growth, alleviating competition among fungi. Resulting feedback loops eventually promote fungal coexistence and synergistic interactions. Nonetheless, overall functional performances are reduced compared to bacteria-free cultures. These findings highlight the necessity to conduct future studies, investigating biodiversity-ecosystem functioning relationships using artificial systems, without exclusion of key organisms naturally co-occurring in the compartment of interest. Otherwise, study outcomes might not reflect true ecological relationships and ultimately misguide conservation strategies.

An overview of Trichoderma reesei co-cultures for the production of lignocellulolytic enzymes

Biorefineries are core facilities for implementing a sustainable circular bioeconomy. These facilities rely on microbial enzymes to hydrolyze lignocellulosic substrates into fermentable sugars. Fungal co-cultures mimic the process of natural biodegradation and have been shown to increase certain enzyme activities. Trichoderma reesei and its many mutant strains are major cellulase producers and are heavily utilized as a source of carbohydrate-active enzymes. Several reports have demonstrated that T. reesei co-cultures present higher enzyme activities compared with its monocultures, especially in the context of β-glucosidase activity. The performance of T. reesei during co-culturing has been assessed with several fungal partners, including Aspergillus niger, one of the most recurrent partners. Various aspects of co-cultivation still need further investigation, especially regarding the molecular interactions between fungi in controlled environments and the optimization of the resulting enzyme cocktails. Since plenty of genetic and physiological data on T. reesei is available, the species is an outstanding candidate for future co-culture investigations. Co-cultures are still a developing field for industrial enzyme production, and many aspects of the technique need further improvement before real applications. KEY POINTS: • T. reesei co-cultures are an alternative for producing lignocellulolytic enzymes. • Several reports suggest an increase in certain enzyme activities in co-cultures. • More in-depth investigations of co-cultures are necessary for advancing this field.

A new atypical short-chain dehydrogenase is required for interfungal combat and conidiation in Trichoderma guizhouense

Hypocrealean Trichoderma are the most extensively studied facultative mycoparasites against phytopathogenic fungi. Aerial hyphae of Trichoderma guizhouense can rapidly proliferate over Fusarium oxysporum hyphae, cause sporadic cell death and arrest the growth of the host. The results of the present study demonstrated that a unique short-chain dehydrogenase/reductase (SDR), designated as TgSDR1, was expressed at a high level in T. guizhouense challenged by the hosts. Similar to other SDRs family members, the TgSDR1 protein contains a cofactor-binding motif and a catalytic site. The subcellular localization assay revealed that the TgSDR1::GFP fusion protein translocated to lipid droplets in mycelia and conidia. The data obtained using reverse genetic approach indicated that TgSDR1 is associated with antifungal ability, plays an important role in providing reducing equivalents in the form of NADPH and regulates the amino sugar and nucleotide sugar metabolism in T. guizhouense upon encountering a host. Moreover, the TgSDR1 deletion mutant was defective in conidiation. Thus, TgSDR1 functions as a key metabolic enzyme in T. guizhouense to regulate mycotrophic interactions, defence against other fungi, such as F. oxysporum, and conidiation.

Variations in sexual fitness among natural strains of the opportunistic human fungal pathogen Aspergillus fumigatus

Aspergillus fumigatus is a ubiquitous ascomycete fungus, naturally inhabiting the soil and compost piles. Its conidia readily disperse into the atmosphere and cause opportunistic infections known as aspergillosis. With the emerging resistance to many antifungal drugs, our understanding of A. fumigatus epidemiology has become increasingly important for developing effective control and treatment strategies. As a pathogen capable of both sexual and asexual reproduction, mutations causing drug resistance and increased virulence could be spread rapidly in A. fumigatus populations. However, relatively little is known about the distributions of sexual reproductive fitness among natural strains of A. fumigatus. Here we investigated the formation of sexual reproductive structure (i.e. cleistothecia) and sexual spore viability among 60 natural strains of A. fumigatus. These strains were from six geographically distant countries (India, China, Canada, Cameroon, Saudi Arabia, and New Zealand), with 10 strains (including five MAT1-1 strains and five MAT1-2 strains) from each country. These strains were crossed in all combinations with strains of the opposite mating type. In addition, all 60 strains were crossed with either AFB62-1 (MAT1-1) or AFIR928 (MAT1-2), two reference supermater strains. Of the 900 crosses among the 60 natural strains, 136 crosses (15.1%) produced cleistothecia. Our analyses revealed that strains from China had the highest average ability to form cleistothecia, followed by those from New Zealand, Saudi Arabia, India, Canada, and Cameroon. Among the crosses that produced cleistothecia, about 40% produced viable ascospores, with the rate of ascospore germination varied significantly among crosses. Interestingly, neither the ability to form cleistothecia nor ascospore germination rate showed any distinct relationships with either geographic or genetic distance between parental strains. Our results suggest that genetic exchange among geographically and genetically divergent strains of A. fumigatus are possible. However, the rates of genetic exchange likely vary among strains and populations in nature.

Cork Oak Endophytic Fungi as Potential Biocontrol Agents against Biscogniauxia mediterranea and Diplodia corticola

An increase in cork oak diseases caused by Biscogniauxia mediterranea and Diplodia corticola has been reported in the last decade. Due to the high socio-economic and ecologic importance of this plant species in the Mediterranean Basin, the search for preventive or treatment measures to control these diseases is an urgent need. Fungal endophytes were recovered from cork oak trees with different disease severity levels, using culture-dependent methods. The results showed a higher number of potential pathogens than beneficial fungi such as cork oak endophytes, even in healthy plants. The antagonist potential of a selection of eight cork oak fungal endophytes was tested against B. mediterranea and D. corticola by dual-plate assays. The tested endophytes were more efficient in inhibiting D. corticola than B. mediterranea growth, but Simplicillium aogashimaense, Fimetariella rabenhorstii, Chaetomium sp. and Alternaria alternata revealed a high potential to inhibit the growth of both. Simplicillium aogashimaense caused macroscopic and microscopic mycelial/hyphal deformations and presented promising results in controlling both phytopathogens' growth in vitro. The evaluation of the antagonistic potential of non-volatile and volatile compounds also revealed that A. alternata compounds could be further explored for inhibiting both pathogens. These findings provide valuable knowledge that can be further explored in in vivo assays to find a suitable biocontrol agent for these cork oak diseases.

Aspects Determining the Dominance of Fomitopsis pinicola in the Colonization of Deadwood and the Role of the Pathogenicity Factor Oxalate

Carbon and mineral cycling in sustainable forest systems depends on a microbiome of basidiomycetes, ascomycetes, litter-degrading saprobes, ectomycorrhizal, and mycoparasitic fungi that constitute a deadwood degrading consortium. The brown rot basidiomycete Fomitopsis pinicola (Swartz: Fr.) P. Karsten (Fp), as an oxalate-producing facultative pathogen, is an early colonizer of wounded trees and fresh deadwood. It replaces basidiomycetous white rot fungi and non-basidiomycetous fungal phyla in the presence of its volatilome, but poorly in its absence. With the goal of determining its dominance over the most competitive basidiomycetes and its role in fungal successions within the forest microbiome in general, Fp was exposed to the white rot fungus Kuehneromyces mutabilis (Schaeff.: Fr.) Singer & Smith (Km) in aseptic dual culture established on fertilized 100 mm-long wood dust columns in glass tubes with the inclusion of their volatilomes. For the mycelia approaching from the opposite ends of the wood dust columns, the energy-generating systems of laccase and manganese peroxidase (MnP), the virulence factor oxalate, and the exhalation of terpenes were determined by spectrophotometry, High Pressure Liquid Chromatography (HPLC), and Gas Chromatography-Mass Spectrometry (GC-MS). Km mycelia perceived the approaching Fp over 20 mm of non-colonized wood dust, reduced the laccase activity to 25%, and raised MnP to 275%–500% by gaining energy and presumably by controlling oxalate, H2O2, and the dropping substrate pH caused by Fp. On mycelial contact, Km stopped Fp, secured its substrate sector with 4 mm of an impermeable barrier region during an eruption of antimicrobial bisabolenes, and dropped from the invasion mode of substrate colonization into the steady state mode of low metabolic and defensive activity. The approaching Fp raised the oxalate production throughout to >20 g kg−1 to inactivate laccase and caused, with pH 1.4–1.7, lethal conditions in its substrate sector whose physiological effects on Km could be reproduced with acidity conditions incited by HCl. After a mean lag phase of 11 days, Fp persisting in a state of high metabolic activity overgrew and digested the debilitated Km thallus and terminated the production of oxalate. It is concluded that the factors contributing to the competitive advantage of F. pinicola in the colonization of wounded trees and pre-infected deadwood are the drastic long-term acidification of the timber substrate, its own insensitivity to extremely low pH conditions, its efficient control of the volatile mono- and sesquiterpenes of timber and microbial origin, and the action of a undefined blend of terpenes and allelopathic substances.

The Third International Symposium on Fungal Stress - ISFUS

Stress is a normal part of life for fungi, which can survive in environments considered inhospitable or hostile for other organisms. Due to the ability of fungi to respond to, survive in, and transform the environment, even under severe stresses, many researchers are exploring the mechanisms that enable fungi to adapt to stress. The International Symposium on Fungal Stress (ISFUS) brings together leading scientists from around the world who research fungal stress. This article discusses presentations given at the third ISFUS, held in São José dos Campos, São Paulo, Brazil in 2019, thereby summarizing the state-of-the-art knowledge on fungal stress, a field that includes microbiology, agriculture, ecology, biotechnology, medicine, and astrobiology.

History of the International Symposium on Fungal Stress - ISFUS, a dream come true!

The International Symposium on Fungal Stress (ISFUS) was born in a dream that Drauzio Eduardo Naretto Rangel had in 2013. This article reviews the first three ISFUSs and prospects for the future meetings. Although ISFUS was born as a small family organized meeting, since the first meeting, ISFUS has achieved great success, receiving very important research grants from FAPESP, FAPEG, and CAPES to bring international scientists to Brazil. Moreover, three special issues in leading journals have been published with articles relating to the talks presented at each ISFUS. For the first meeting, most speakers published in a special issue in Current Genetics. From the second and third meeting, articles from the speakers were published in special issues of the top mycology journal, Fungal Biology, published by Elsevier on behalf of the British Mycological Society. Here we show that following the dreams with a full heart and adding lots of love, passion, and hard work can achieve success.

Discovery of Antifungal and Biofilm Preventative Compounds from Mycelial Cultures of a Unique North American Hericium sp. Fungus

Edible mushrooms are an important source of nutraceuticals and for the discovery of bioactive metabolites as pharmaceuticals. In this work, the OSMAC (One Strain, Many Active Compounds) approach was used to isolate two new compounds (1 and 2) along with seven known compounds (3–9) from a mycelial culture of a unique North American edible mushroom Hericium sp. The fruiting body was collected in Marine on St. Croix, Minnesota (USA), and mycelial cultures were grown on four different solid and liquid media. Extracts from the mycelial cultures were screened for antimicrobial activity and only the extract from the Cheerios substrate culture exhibited antifungal activity. Bioassay guided fractionation and HPLC analysis were used to isolate nine pure compounds and the structures of the known compounds were established by analysis of the NMR and mass spectrometry data and comparison to published reports. Compound 1 is a new erinacerin alkaloid and 2 is an aldehyde derivative of 4-hydroxy chroman. Four chlorinated orcinol derivatives (3–6), a pyran (7), erinaceolactone (8), and erinacine (9) were identified. Compound 4 showed antifungal activity against C. albicans and C. neoformans (MIC = 31.3–62.5 μg/mL, respectively). Compound 4 also inhibited biofilm formation of C. albicans and C. neoformans at 7.8 μg/mL. These results suggest that mycelial cultures of edible fungi may provide useful, bioactive compounds.

Type I and II PRMTs regulate catabolic as well as detoxifying processes in Aspergillus nidulans

In filamentous fungi, arginine methylation has been implicated in morphogenesis, mycotoxin biosynthesis, pathogenicity, and stress response although the exact role of this posttranslational modification in these processes remains obscure. Here, we present the first genome-wide transcriptome analysis in filamentous fungi that compared expression levels of genes regulated by type I and type II protein arginine methyltransferases (PRMTs). In Aspergillus nidulans, three conserved type I and II PRMTs are present that catalyze asymmetric or symmetric dimethylation of arginines. We generated a double type I mutant (ΔrmtA/rmtB) and a combined type I and type II mutant (ΔrmtB/rmtC) to perform genome-wide comparison of their effects on gene expression, but also to monitor putative overlapping activities and reciprocal regulations of type I and type II PRMTs in Aspergillus. Our study demonstrates, that rmtA and rmtC as type I and type II representatives act together as repressors of proteins that are secreted into the extracellular region as the majority of up-regulated genes are mainly involved in catabolic pathways that constitute the secretome of Aspergillus. In addition to a strong up-regulation of secretory genes we found a significant enrichment of down-regulated genes involved in processes related to oxidation-reduction, transmembrane transport and secondary metabolite biosynthesis. Strikingly, nearly 50% of down-regulated genes in both double mutants correspond to redox reaction/oxidoreductase processes, a remarkable finding in light of our recently observed oxidative stress phenotypes of ΔrmtA and ΔrmtC. Finally, analysis of nuclear and cytoplasmic extracts for mono-methylated proteins revealed the presence of both, common and specific substrates of RmtA and RmtC. Thus, our data indicate that type I and II PRMTs in Aspergillus seem to co-regulate the same biological processes but also specifically affect other pathways in a non-redundant fashion.

Guttation capsules containing hydrogen peroxide: an evolutionarily conserved NADPH oxidase gains a role in wars between related fungi

When resources are limited, the hypocrealean fungus Trichoderma guizhouense can overgrow another hypocrealean fungus Fusarium oxysporum, cause sporadic cell death and arrest growth. A transcriptomic analysis of this interaction shows that T. guizhouense undergoes a succession of metabolic stresses while F. oxysporum responded relatively neutrally but used the constitutive expression of several toxin‐encoding genes as a protective strategy. Because of these toxins, T. guizhouense cannot approach it is potential host on the substrate surface and attacks F. oxysporum from above. The success of T. guizhouense is secured by the excessive production of hydrogen peroxide (H₂O₂), which is stored in microscopic bag‐like guttation droplets hanging on the contacting hyphae. The deletion of NADPH oxidase nox1 and its regulator, nor1 in T. guizhouense led to a substantial decrease in H₂O₂ formation with concomitant loss of antagonistic activity. We envision the role of NOX proteins in the antagonism of T. guizhouense as an example of metabolic exaptation evolved in this fungus because the primary function of these ancient proteins was probably not linked to interfungal relationships. In support of this, F. oxysporum showed almost no transcriptional response to T. guizhouense Δnox1 strain indicating the role of NOX/H₂O₂ in signalling and fungal communication.

Gongronella sp. w5 elevates Coprinopsis cinerea laccase production by carbon source syntrophism and secondary metabolite induction

When sucrose was used as the carbon source, the Basidiomycete Coprinopsis cinerea showed poor growth and low laccase activity in pure culture, but greatly enhanced the level of laccase activity (>1800 U/L) during coculture with the Mucoromycete Gongronella sp. w5. As a result, the mechanism of laccase overproduction in coculture was investigated by starting from clarifying the function of sucrose. Results demonstrated that Gongronella sp. w5 in the coculture system hydrolyzed sucrose to glucose and fructose by an intracellular invertase. Fructose rather than glucose was supplied by Gongronella sp. w5  as the readily available carbon source for C. cinerea, and contributed to an alteration of its growth behavior and a basal laccase secretion of 110.6 ± 3.3 U/L. On the other hand, separating Gongronella sp. w5 of C. cinerea by transfer into dialysis tubes yielded the same level of laccase activity as without separation, indicating that enhanced laccase production probably resulted from the metabolites in the fermentation broth. Further investigation showed that the ethyl acetate-extracted metabolites generated by Gongronella sp. w5 induced C. cinerea laccase production. One of the laccase-inducing compounds namely p-hydroxybenzoic acid (HBA) was purified and identified from the extract. When using HBA as the inducer and fructose as the carbon source in monoculture, C. cinerea observed similar high laccase activity to that in coculture, and zymograms revealed the same expression of laccase Lcc9 as the main and Lcc1 and Lcc5 as the minor enzymes. Overall, our experiments verified that Gongronella sp. w5 elevates Coprinopsis cinerea laccase production by carbon source syntrophism and secondary metabolite induction.