Re-identification of the ascofuranone-producing fungus Ascochyta viciae as Acremonium sclerotigenum

Prophylactic activity of orally administered dry-heat-sterilized Acremonium egyptiacum against Trypanosoma congolense-induced animal African trypanosomosis

Animal African trypanosomosis (AAT) is an important global disease of livestock that causes economic losses of up to 4.5 billion US dollars per year. Thus, eliminating AAT in endemic countries will improve agricultural productivity and economic growth. To prevent AAT, vector control and the development of prophylactic drugs are crucial. Ascofuranone (AF) is a bioactive fungal compound with proven in vitro trypanocidal potency and in vivo treatment efficacy. However, the complex stereoselective synthesis of AF has prevented its cost-effective industrial production. Recently, a genetically modified strain of Acremonium egyptiacum fungus that produces a high yield of AF was developed. Therefore, we hypothesized that the oral administration of the AF-producing fungus itself may be effective against AAT. Hence, this study aimed to evaluate the prophylactic activity of orally administered dry-heat-sterilized A. egyptiacum against Trypanosoma congolense IL3000 infection using a mouse model. The survival rate was significantly prolonged (p = 0.009), and parasitemia was suppressed in all AF-fungus-treated groups (Group 1-9) compared with that in the untreated control group (Group 10). Hence, the trypanocidal activity of AF was retained after dry-heat-sterilization of the AF-producing fungus and that its oral administration effectively prevented AAT. Since AAT is endemic to rural areas with underdeveloped veterinary infrastructure, dry-heat-sterilized A. egyptiacum would be the most cost-effective potential treatment for AAT.

Pesticide-tolerant microbial consortia: Potential candidates for remediation/clean-up of pesticide-contaminated agricultural soil

Reclamation of pesticide-polluted lands has long been a difficult endeavour. The use of synthetic pesticides could not be restricted due to rising agricultural demand. Pesticide toxicity has become a pressing agronomic problem due to its adverse impact on agroecosystems, agricultural output, and consequently food security and safety. Among different techniques used for the reclamation of pesticide-polluted sites, microbial bioremediation is an eco-friendly approach, which focuses on the application of resilient plant growth promoting rhizobacteria (PGPR) that may transform or degrade chemical pesticides to innocuous forms. Such pesticide-resilient PGPR has demonstrated favourable effects on soil-plant systems, even in pesticide-contaminated environments, by degrading pesticides, providing macro-and micronutrients, and secreting active but variable secondary metabolites like-phytohormones, siderophores, ACC deaminase, etc. This review critically aims to advance mechanistic understanding related to the reduction of phytotoxicity of pesticides via the use of microbe-mediated remediation techniques leading to crop optimization in pesticide-stressed soils. The literature surveyed and data presented herein are extremely useful, offering agronomists-and crop protectionists microbes-assisted remedial strategies for affordably enhancing crop productivity in pesticide-stressed soils.

Filamentous Fungi-Derived Orsellinic Acid-Sesquiterpene Meroterpenoids: Fungal Sources, Chemical Structures, Bioactivities, and Biosynthesis

Fungi-derived polyketide-terpenoid hybrids are important meroterpenoid natural products that possess diverse structure scaffolds with a broad spectrum of bioactivities. Herein, we focus on an ever-increasing group of meroterpenoids, orsellinic acid-sesquiterpene hybrids comprised of biosynthetic start unit orsellinic acid coupling to a farnesyl group or/and its modified cyclic products. The review entails the search of China National Knowledge Infrastructure (CNKI), Web of Science, Science Direct, Google Scholar, and PubMed databases up to June 2022. The key terms include "orsellinic acid", "sesquiterpene", "ascochlorin", "ascofuranone", and "Ascochyta viciae", which are combined with the structures of "ascochlorin" and "ascofuranone" drawn by the Reaxys and Scifinder databases. In our search, these orsellinic acid-sesquiterpene hybrids are mainly produced by filamentous fungi. Ascochlorin was the first compound reported in 1968 and isolated from filamentous fungus Ascochyta viciae (synonym: Acremonium egyptiacum; Acremonium sclerotigenum); to date, 71 molecules are discovered from various filamentous fungi inhabiting in a variety of ecological niches. As typical representatives of the hybrid molecules, the biosynthetic pathway of ascofuranone and ascochlorin are discussed. The group of meroterpenoid hybrids exhibits a broad arrange of bioactivities, as highlighted by targeting hDHODH (human dihydroorotate dehydrogenase) inhibition, antitrypanosomal, and antimicrobial activities. This review summarizes the findings related to the structures, fungal sources, bioactivities, and their biosynthesis from 1968 to June 2022.

Killing Two Birds with One Stone: Discovery of Dual Inhibitors of Oxygen and Fumarate Respiration in Zoonotic Parasite, Echinococcus multilocularis

Ascofuranone (AF), a meroterpenoid isolated from various filamentous fungi, including Acremonium egyptiacum, has been reported as a potential lead candidate for drug development against parasites and cancer. In this study, we demonstrated that AF and its derivatives are potent anthelminthic agents, particularly against Echinococcus multilocularis, which is the causative agent of alveolar echinococcosis. We measured the inhibitory activities of AF and its derivatives on the mitochondrial aerobic and anaerobic respiratory systems of E. multilocularis larvae. Several derivatives inhibited complex II (succinate:quinone reductase [SQR]; IC₅₀ = 0.037 to 0.135 μM) and also complex I to III (NADH:cytochrome c reductase; IC₅₀ = 0.008 to 0.401 μM), but not complex I (NADH:quinone reductase), indicating that mitochondrial complexes II and III are the targets. In particular, complex II inhibition in the anaerobic pathway was notable because E. multilocularis employs NADH:fumarate reductase (fumarate respiration), in addition to NADH oxidase (oxygen respiration), resulting in complete shutdown of ATP synthesis by oxidative phosphorylation. A structure-activity relationship study of E. multilocularis complex II revealed that the functional groups of AF are essential for inhibition. Binding mode prediction of AF derivatives to complex II indicated potential hydrophobic and hydrogen bond interactions between AF derivatives and amino acid residues within the quinone binding site. Ex vivo culture assays revealed that AF derivatives progressively reduced the viability of protoscoleces under both aerobic and anaerobic conditions. These findings confirm that AF and its derivatives are the first dual inhibitors of fumarate and oxygen respiration in E. multilocularis and are potential lead compounds in the development of anti-echinococcal drugs.

Heterologous production of ascofuranone and ilicicolin A in Aspergillus sojae

Ascofuranone and its precursor, ilicicolin A, are secondary metabolites with various pharmacological activities that are produced by Acremonium egyptiacum. In particular, ascofuranone strongly inhibits trypanosome alternative oxidase and represents a potential drug candidate against African trypanosomiasis. However, difficulties associated with industrial production of ascofuranone by A. egyptiacum, specifically the co-production of ascochlorin, which inhibits mammalian respiratory chain complex III at low concentrations, has precluded its widespread application. Therefore, in this study, ascofuranone biosynthetic genes (ascA-E and H-J) were heterologously expressed in Aspergillus sojae, which produced very low-levels of endogenous secondary metabolites under conventional culture conditions. As a result, although we obtained transformants producing both ilicicolin A and ascofuranone, they were produced only when an adequate concentration of chloride ions was added to the medium. In addition, we succeeded in increasing the production of ilicicolin A, by enhancing the expression of the rate-determining enzyme AscD, using a multi-copy integration system. The heterologous expression approach described here afforded the production of both ascofuranone and ilicicolin A, allowing for their development as therapeutics.

Biochemical Studies of Mitochondrial Malate: Quinone Oxidoreductase from Toxoplasma gondii

Toxoplasma gondii is a protozoan parasite that causes toxoplasmosis and infects almost one-third of the global human population. A lack of effective drugs and vaccines and the emergence of drug resistant parasites highlight the need for the development of new drugs. The mitochondrial electron transport chain (ETC) is an essential pathway for energy metabolism and the survival of T. gondii. In apicomplexan parasites, malate:quinone oxidoreductase (MQO) is a monotopic membrane protein belonging to the ETC and a key member of the tricarboxylic acid cycle, and has recently been suggested to play a role in the fumarate cycle, which is required for the cytosolic purine salvage pathway. In T. gondii, a putative MQO (TgMQO) is expressed in tachyzoite and bradyzoite stages and is considered to be a potential drug target since its orthologue is not conserved in mammalian hosts. As a first step towards the evaluation of TgMQO as a drug target candidate, in this study, we developed a new expression system for TgMQO in FN102(DE3)TAO, a strain deficient in respiratory cytochromes and dependent on an alternative oxidase. This system allowed, for the first time, the expression and purification of a mitochondrial MQO family enzyme, which was used for steady-state kinetics and substrate specificity analyses. Ferulenol, the only known MQO inhibitor, also inhibited TgMQO at IC₅₀ of 0.822 μM, and displayed different inhibition kinetics compared to Plasmodium falciparum MQO. Furthermore, our analysis indicated the presence of a third binding site for ferulenol that is distinct from the ubiquinone and malate sites.

Antiparasitic antibiotics from Japan

Antibiotics are microbial secondary metabolites and they are important for the treatment of infectious diseases. Japanese researchers have made a large contribution to studies of antibiotics, and they have also been important in the discovery of antiparasitic antibiotics. Satoshi Ōmura received the Nobel Prize in 2015 for the "discoveries concerning a novel therapy against infections caused by roundworm parasites", which means discovery of a new nematocidal antibiotic, avermectin. Here, I review the many antiparasitic antibiotics and their lead compounds that have been discovered for use in human and veterinary medicine.

Bioactive Ascochlorin Analogues from the Marine-Derived Fungus Stilbella fimetaria

The marine-derived fungus Stilbella fimetaria is a chemically talented fungus producing several classes of bioactive metabolites, including meroterpenoids of the ascochlorin family. The targeted dereplication of fungal extracts by UHPLC-DAD-QTOF-MS revealed the presence of several new along with multiple known ascochlorin analogues (19–22). Their structures and relative configuration were characterized by 1D and 2D NMR. Further targeted dereplication based on a novel 1,4-benzoquinone sesquiterpene derivative, fimetarin A (22), resulted in the identification of three additional fimetarin analogues, fimetarins B–D (23–25), with their tentative structures proposed from detailed MS/HRMS analysis. In total, four new and eight known ascochlorin/fimetarin analogues were tested for their antimicrobial activity, identifying the analogues with a 5-chloroorcylaldehyde moiety to be more active than the benzoquinone analogue. Additionally, the presence of two conjugated double bonds at C-2′/C-3′ and C-4′/C-5′ were found to be essential for the observed antifungal activity, whereas the single, untailored bonds at C-4′/C-5′ and C-8′/C-9′ were suggested to be necessary for the observed antibacterial activity.

Phytotoxic Metabolites Produced by Legume-Associated Ascochyta and Its Related Genera in the Dothideomycetes

Phytotoxins, secondary metabolites toxic to plants and produced by fungi, are believed to play an important role in disease development by targeting host cellular machineries and/or interfering with host immune responses. The Ascochyta blight diseases on different legume plants are caused by Ascochyta and related taxa, such as Phoma. The causal agents of the Ascochyta blight are often associated with specific legume plants, showing a relatively narrow host range. The legume-associated Ascochyta and Phoma are known to produce a diverse array of polyketide-derived secondary metabolites, many of which exhibited significant phytotoxicity and have been claimed as virulence or pathogenicity factors. In this article, we reviewed the current state of knowledge on the diversity and biological activities of the phytotoxic compounds produced by Ascochyta and Phoma species. Also, we touched on the secondary metabolite biosynthesis gene clusters identified thus far and discussed the role of metabolites in the fungal biology.

The High Diversity and Variable Susceptibility of Clinically Relevant Acremonium-Like Species in China

Acremonium-like fungi are emerging as important opportunistic pathogens in cutaneous, subcutaneous and serious invasive infections, especially in immunocompromised and debilitated individuals, and Acremonium infections are usually resistant to antifungal therapy. Several molecular studies have demonstrated that many species in the genus Acremonium are polyphyletic, and currently, the genus is restricted to the family Bionectriaceae (Hypocreales). Molecular identification and in vitro antifungal susceptibility tests of Acremonium-like fungi isolated from human clinical specimens in China were performed in this study. Three genetic loci: the large subunit ribosomal RNA gene (LSU), ribosomal internal transcribed spacer and elongation factor 1-α (EF1-α), were used to assess their taxonomic position for correct identification among various species. The multilocus study of twenty-eight strains showed that these strains were distributed in three main lineages: egyptiacum, Cordycipitaceae and Sarocladium; Acremonium egyptiacum and Sarocladium kiliense were the main species of these strains, and three isolates were too phylogenetically distant to be considered undescribed species. Relatively low minimum inhibitory concentrations (MICs) of 0.25-2 and 0.031-0.5 μg/mL were found for voriconazole and terbinafine for most species, respectively. Varied antifungal activities of ciclopirox olamine, amorolfine and posaconazole were found in our study. However, no antifungal effect of sertaconazole, itraconazole or fluconazole was observed against most strains. This is the first study on Acremonium-like species diversity by multilocus sequence analyses and antifungal susceptibility of clinically relevant isolates in China.

Complete biosynthetic pathways of ascofuranone and ascochlorin in Acremonium egyptiacum

Ascofuranone (AF) and ascochlorin (AC) are meroterpenoids produced by various filamentous fungi, including Acremonium egyptiacum (synonym: Acremonium sclerotigenum), and exhibit diverse physiological activities. In particular, AF is a promising drug candidate against African trypanosomiasis and a potential anticancer lead compound. These compounds are supposedly biosynthesized through farnesylation of orsellinic acid, but the details have not been established. In this study, we present all of the reactions and responsible genes for AF and AC biosyntheses in A. egyptiacum, identified by heterologous expression, in vitro reconstruction, and gene deletion experiments with the aid of a genome-wide differential expression analysis. Both pathways share the common precursor, ilicicolin A epoxide, which is processed by the membrane-bound terpene cyclase (TPC) AscF in AC biosynthesis. AF biosynthesis branches from the precursor by hydroxylation at C-16 by the P450 monooxygenase AscH, followed by cyclization by a membrane-bound TPC AscI. All genes required for AC biosynthesis (ascABCDEFG) and a transcriptional factor (ascR) form a functional gene cluster, whereas those involved in the late steps of AF biosynthesis (ascHIJ) are present in another distantly located cluster. AF is therefore a rare example of fungal secondary metabolites requiring multilocus biosynthetic clusters, which are likely to be controlled by the single regulator, AscR. Finally, we achieved the selective production of AF in A. egyptiacum by genetically blocking the AC biosynthetic pathway; further manipulation of the strain will lead to the cost-effective mass production required for the clinical use of AF.

Insights into the ubiquinol/dioxygen binding and proton relay pathways of the alternative oxidase

The alternative oxidase (AOX) is a monotopic diiron carboxylate protein which catalyzes the four-electron reduction of dioxygen to water by ubiquinol. Although we have recently determined the crystal structure of Trypanosoma brucei AOX (TAO) in the presence and absence of ascofuranone (AF) derivatives (which are potent mixed type inhibitors) the mechanism by which ubiquinol and dioxygen binds to TAO remain inconclusive. In this article, ferulenol was identified as the first competitive inhibitor of AOX which has been used to probe the binding of ubiquinol. Surface plasmon resonance reveals that AF is a quasi-irreversible inhibitor of TAO whilst ferulenol binding is completely reversible. The structure of the TAO-ferulenol complex, determined at 2.7 Å, provided insights into ubiquinol binding and has also identified a potential dioxygen molecule bound in a side-on conformation to the diiron center for the first time.

4-O-carboxymethylascochlorin protected against microglial-mediated neurotoxicity in SH-SY5Y and BV2 cocultured cells from LPS-induced neuroinflammation and death by inhibiting MAPK, NF-κB, and Akt pathways

In our previous studies, structurally similar compounds of ascochlorin and ascofuranone exhibited anti-inflammatory activity. Neural inflammation plays a significant role in the commence and advancement of neurodegenerative diseases. It is not known whether 4-O-carboxymethylascochlorin (AS-6) regulates the initial stage of inflammatory responses at the cellular level in BV2 microglia cells. We here investigated the anti-inflammatory effects of AS-6 treatment in microglia cells with the microglial protection in neurons. We found that the lipopolysaccharide (LPS)-stimulated production of nitric oxide, a main regulator of inflammation, is suppressed by AS-6 in BV2 microglial cells. In addition, AS-6 dose-dependently suppressed the increase in COX-2 protein and messenger RNA levels in LPS-stimulated BV2 cells. Moreover, AS-6 inhibited the expression and secretion of proinflammatory cytokines in BV2 microglial cells. At the intracellular level, AS-6 inhibited LPS-activated nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in BV2 microglial cells. AS-6 negatively affected mitogen-activated protein kinases (MAPK) and Akt phosphorylation: Phosphorylated forms of ERK, JNK, p38, and Akt decreased. To check whether AS-6 protects against inflammatory inducer-mediated neurotoxicity, neuronal SH-SY5Y cells were coincubated with BV2 cells in conditioned medium. AS-6 exerted a neuroprotective effect by suppressing microglial activation by LPS or amyloid-β peptide. AS-6 is a promising suppressor of inflammatory responses in LPS-induced BV2 cells by attenuating NF-κB and MAPKs signaling. AS-6 protected against microglial-mediated neurotoxicity in SH-SY5Y and BV2 cocultured cells from LPS-induced neuroinflammation and death via inhibiting MAPK, NF-κB, and Akt pathways.

Alternative oxidase inhibitors: Mitochondrion-targeting as a strategy for new drugs against pathogenic parasites and fungi

The alternative oxidase (AOX) is a ubiquitous terminal oxidase of plants and many fungi, catalyzing the four-electron reduction of oxygen to water alongside the cytochrome-based electron transfer chain. Unlike the classical electron transfer chain, however, the activity of AOX does not generate adenosine triphosphate but has functions such as thermogenesis and stress response. As it lacks a mammalian counterpart, it has been investigated intensely in pathogenic fungi. However, it is in African trypanosomes, which lack cytochrome-based respiration in their infective stages, that trypanosome alternative oxidase (TAO) plays the central and essential role in their energy metabolism. TAO was validated as a drug target decades ago and among the first inhibitors to be identified was salicylhydroxamic acid (SHAM), which produced the expected trypanocidal effects, especially when potentiated by coadministration with glycerol to inhibit anaerobic energy metabolism as well. However, the efficacy of this combination was too low to be of practical clinical use. The antibiotic ascofuranone (AF) proved a much stronger TAO inhibitor and was able to cure Trypanosoma vivax infections in mice without glycerol and at much lower doses, providing an important proof of concept milestone. Systematic efforts to improve the SHAM and AF scaffolds, aided with the elucidation of the TAO crystal structure, provided detailed structure-activity relationship information and reinvigorated the drug discovery effort. Recently, the coupling of mitochondrion-targeting lipophilic cations to TAO inhibitors has dramatically improved drug targeting and trypanocidal activity while retaining target protein potency. These developments appear to have finally signposted the way to preclinical development of TAO inhibitors.

Selective Cytotoxicity of Dihydroorotate Dehydrogenase Inhibitors to Human Cancer Cells Under Hypoxia and Nutrient-Deprived Conditions

Human dihydroorotate dehydrogenase (HsDHODH) is a key enzyme of pyrimidine de novo biosynthesis pathway. It is located on the mitochondrial inner membrane and contributes to the respiratory chain by shuttling electrons to the ubiquinone pool. We have discovered ascofuranone (1), a natural compound produced by Acremonium sclerotigenum, and its derivatives are a potent class of HsDHODH inhibitors. We conducted a structure–activity relationship study and have identified functional groups of 1 that are essential for the inhibition of HsDHODH enzymatic activity. Furthermore, the binding mode of 1 and its derivatives to HsDHODH was demonstrated by co-crystallographic analysis and we show that these inhibitors bind at the ubiquinone binding site. In addition, the cytotoxicities of 1 and its potent derivatives 7, 8, and 9 were studied using human cultured cancer cells. Interestingly, they showed selective and strong cytotoxicity to cancer cells cultured under microenvironment (hypoxia and nutrient-deprived) conditions. The selectivity ratio of 8 under this microenvironment show the most potent inhibition which was over 1000-fold higher compared to that under normal culture condition. Our studies suggest that under microenvironment conditions, cancer cells heavily depend on the pyrimidine de novo biosynthesis pathway. We also provide the first evidence that 1 and its derivatives are potential lead candidates for drug development which target the HsDHODH of cancer cells living under a tumor microenvironment.

The Protean Acremonium. A. sclerotigenum/egyptiacum: Revision, Food Contaminant, and Human Disease

Acremonium is known to be regularly isolated from food and also to be a cause of human disease. Herein, we resolve some sources of confusion that have strongly hampered the accurate interpretation of these and other isolations. The recently designated type species of the genus Acremonium, A. alternatum, is known only from a single isolate, but it is the closest known relative of what may be one of the planet's most successful organisms, Acremonium sclerotigenum/egyptianum, shown herein to be best called by its earliest valid name, A. egyptiacum. The sequencing of ribosomal internal transcribed spacer (ITS) regions, actin genes, or both for 72 study isolates within this group allowed the full range of morphotypes and ITS barcode types to be elucidated, along with information on temperature tolerance and habitat. The results showed that nomenclatural confusion and frequent misidentifications facilitated by morphotaxonomy, along with misidentified early sequence deposits, have obscured the reality that this species is, in many ways, the definitive match of the historical concept of Acremonium: a pale orange or dull greenish-coloured monophialidic hyphomycete, forming cylindrical, ellipsoidal, or obovoid conidia in sticky heads or obovoid conidia in dry chains, and acting ecologically as a soil organism, marine organism, plant pathogen, plant endophyte, probable insect pathogen, human opportunistic pathogen, food contaminant, probable dermatological communicable disease agent, and heat-tolerant spoilage organism. Industrially, it is already in exploratory use as a producer of the antibiotic ascofuranone, active against trypanosomes, cryptosporidia, and microsporidia, and additional applications are in development. The genus-level clarification of the phylogeny of A. egyptiacum shows other historic acremonia belong to separate genera, and two are here described, Parasarocladium for the Acremonium radiatum complex and Kiflimonium for the Acremonium curvulum complex.

Stilbocrea walteri sp. nov., an unusual species of Bionectriaceae

The new species Stilbocrea walteri is described and illustrated from Quercus ilex collected in Portugal. Phylogenetic analyses of LSU rDNA, rpb1, rpb2 and tef1 sequence matrices place S. walteri in the Bionectriaceae, Hypocreales, within a clade of specimens morphologically identified as Stilbocrea macrostoma, the generic type of Stilbocrea. Stilbocrea walteri differs from S. macrostoma in dark olive green to blackish ascomata basally immersed in a stroma, KOH+ and LA+ ascomata and the lack of a stilbella-like asexual morph on natural substrate and pure culture. A simple phialidic asexual morph is formed in pure culture. To enable a morphological comparison, Stilbocrea macrostoma is illustrated.

Combinatorial Biosynthesis of (+)-Daurichromenic Acid and Its Halogenated Analogue

Daurichromenic acid is a meroterpenoid with various pharmacological activities that is biosynthesized from grifolic acid in Rhododendron dauricum. Heterologous expression of grifolic acid synthases from Stachybotrys bisbyi and a daurichromenic acid synthase from R. dauricum in Aspergillus oryzae mediated three-step combinatorial biosynthesis of (+)-daurichromenic acid through enantioselective 6-endo-trig cyclization. Additional introduction of a halogenase from Fusarium sp. into the strain resulted in the biosynthesis of (+)-5-chlorodaurichromenic acid, which exceeds the antibacterial activity of the original compounds.