Bikaverin production and applications

Safety evaluation of a food enzyme containing phospholipase activity produced by a strain of Fusariumcommune

Phospholipases are commonly used food enzymes, e.g. to improve bread-making properties. For organic food certifications, enzymes need to be produced by non-genetically modified organisms, but no such 'classical' phospholipases are currently available. To this aim, a phospholipase product was developed with a Fusarium commune strain, a microorganism having no reported uses in the food industry. The safety of microbially-derived food enzymes depends largely on the safety of the production strain. Strain F. commune LFC was obtained by classical strain improvement. Whole-Genome Sequencing and literature search allowed to identify potential gene clusters for the mycotoxins beauvericin (BEA), moniliformin (MON), and fusaric acid (FA). Analysis of these mycotoxins revealed that no toxicologically relevant levels were produced during controlled submerged fermentation. The enzyme concentrate was assessed in a range of toxicity studies. The Ames test (OECD 471) was concluded to be equivocal, but the ToxTracker® AO assay suggested an indirect mode of action, induced by dose-dependent oxidative stress. The in vitro micronucleus test (OECD 487) and the in vivo follow-up Comet assay (OECD 489) confirmed that the food enzyme was not genotoxic. The repeated-dose oral toxicity study (OECD 408) showed no adverse effects in any of the treatment groups and allowed to derive a NOAEL of 1124 mg TOS/kg bw/day. The Margin of Exposure with estimated dietary intakes in human food applications was determined to be > 2500. It is therefore concluded that the use of the phospholipase enzyme LFC as processing aid in baking and other cereal-based applications is safe.

Bikaverin as a molecular weapon: enhancing Fusarium oxysporum pathogenicity in bananas via rhizosphere microbiome manipulation

BACKGROUND

Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense Tropical Race 4 (Foc TR4), poses a severe threat to global banana production. Secondary metabolites are critical tools employed by pathogens to interact with their environment and modulate host-pathogen dynamics. Bikaverin, a red-colored polyketide pigment produced by several Fusarium species, has been studied for its pharmacological properties, but its ecological roles and impact on pathogenicity remain unclear.

RESULTS

This study investigated the role of bikaverin in Foc TR4, focusing on its contribution to pathogenicity and its interaction with the rhizosphere microbiome. Pathogenicity assays under sterile and autoclaved conditions demonstrated that bikaverin does not directly contribute to pathogenicity by affecting the infection process or damaging host tissues. Instead, bikaverin indirectly enhances Foc TR4's pathogenicity by reshaping the rhizosphere microbiome. It suppresses beneficial plant growth-promoting rhizobacteria, such as Bacillus, while promoting the dominance of fungal genera, thereby creating a microbial environment beneficial for pathogen colonization and infection. Notably, bikaverin biosynthesis was found to be tightly regulated by environmental cues, including acidic pH, nitrogen scarcity, and microbial competition. Co-culture with microbes such as Bacillus velezensis and Botrytis cinerea strongly induced bikaverin production and upregulated expression of the key bikaverin biosynthetic gene FocBik1. In addition, the identification of bikaverin-resistant Bacillus BR160, a strain with broad-spectrum antifungal activity, highlights its potential as a biocontrol agent for banana wilt management, although its stability and efficiency under field conditions require further validation.

CONCLUSIONS

Bikaverin plays an indirect yet important role in the pathogenicity of Foc TR4 by manipulating the rhizosphere microbiome. This ecological function underscores its potential as a target for sustainable disease management strategies. Future research should focus on elucidating the molecular mechanisms underlying bikaverin-mediated microbial interactions, using integrated approaches such as transcriptomics and metabolomics. Together, these findings provide a foundation for novel approaches to combat banana wilt disease and enhance crop resistance. Video Abstract.

Unveiling the Substrate-Dependent Dynamics of Mycotoxin Production in Fusarium verticillioides Using an OSMAC-Metabolomics Approach

Fusarium verticillioides is a prevalent plant pathogenic fungus known to produce harmful mycotoxins, including fumonisins and emerging toxins. This study aimed to investigate the influence of substrate on the temporal patterns of mycotoxin biosynthesis by F. verticillioides, employing a combined OSMAC (One Strain-Many Compounds) strategy and metabolomics approach. The fungus was cultured under various media conditions, and samples were collected over time. LC-MS/MS analyses and a dereplicative workflow were used to profile the secondary metabolite production, focusing on mycotoxins. The results demonstrated that modifying the culture conditions led to significant variations in fungal growth and the nature and relative concentrations of mycotoxins produced. Corn meal agar (CMA) medium was favorable for fumonisins A1 and B1, while malt extract agar (MEA) favored fumonisins A2 and B2. The study also identified the production of other mycotoxins related compounds as fusarins, bikaverin derivatives and fumonisins analogs, under different growth conditions. This study highlights the potential of combining OSMAC and metabolomics to unravel the substrate-dependent and time-dependent variations in mycotoxin biosynthesis by F. verticillioides. The insights gained provide a better understanding of the ecophysiology of this fungus and the occurrence of its mycotoxins, which can inform targeted mitigation strategies to ensure food and feed safety.

The blue palette of life: A comprehensive review of natural bluish colorants with potential commercial applications

Considering the growing interest for safer, environmentally friendly and healthier products, the search for natural colorants to replace their synthetic has been raised. This is particularly challenging for the rare and usually unstable bluish coloring substances. This comprehensive review describes several bluish pigments which can be obtained from natural sources (plants and mostly microorganisms), covering less known molecules to well established compounds (although no focus is given for anthocyanins). Key information about each compound, including sources, extraction procedures, properties, and potential applications, are presented. Despite many studies on these molecules, toxicological and stability studies are still lacking for many of them. Therefore, this text also discusses the regulatory requirements for approving new coloring substances. Given the increasing robustness of scientific data supporting the biological activities attributed to many of these pigments, it is possible to envisage that some of them may be commercially available for industrial applications in different fields, not only in traditional food or cosmetic uses but in pharmaceutical formulations as well.

Insights into the genomic architecture of a newly discovered endophytic Fusarium species belonging to the Fusarium concolor complex from India

In this study, a new species Fusarium indicum belonging to the Fusarium concolor species complex is established to accommodate an endophytic fungus isolated from Bambusa sp. and collected from Himachal Pradesh. The identity of this isolate was confirmed based on the asexual morphs, its cultural characteristics, and phylogenetic analyses. This isolate revealed out to be distinct by showing less similarity with described species in the genus Fusarium based on molecular sequence data, approximately 93.9% similarity based on translation elongation factor 1-alpha, and 94.2% similarity based on RNA polymerase II subunit. Furthermore, to increase knowledge about this novel species, whole-genome sequencing was carried out. The results displayed that Fusarium indicum NFCCI 5145 possesses a 40.2 Mb genome and 48.39% of GC content. Approximately 12,963 functional protein-coding genes were carefully predicted and annotated using different BLAST databases, such as Uniprot, Kyoto Encyclopedia of Genes and Genomes (KEGG), Gene Ontology (GO), Pathogen Host Interactions (PHI), Clusters of Orthologous Groups (COG), and Carbohydrate-Active enzymes (CAZy). The orthologous proteins were identified using OrthoFinder and used for the phylogenetic analysis. ANIb confirmed that the isolate is closely related to the F. concolor species complex. It is known that Fusarium strains can produce a wide range of bioactive secondary metabolites. Therefore, in-depth mining for biosynthetic gene clusters for secondary metabolite biosynthesis of Fusarium indicum NFCCI 5145 was investigated using Antibiotics and Secondary Metabolites Analysis Shell (AntiSMASH) annotation. AntiSMASH results displayed that this isolate possesses 45 secondary metabolites of biosynthetic gene clusters (BGCs). These findings significantly improved our understanding of the strain Fusarium indicum NFCCI 5145 and its possible applications in different sectors including industry for the secondary metabolites and enzymes it can produce.

Codeine dysregulates ribosome biogenesis in Escherichia coli with DNA double-strand breaks to chart path to new classes of antibiotics

Aim

A bacterial genetics-guided approach was utilized for the discovery of new compounds affecting bacterial genome stability.

Materials & methods

Fungal extracts and fractions were tested for genome instability-mediated antibacterial activity. Interaction assays and RT-qPCR were used to identify compounds that boost the activity of sub-minimum inhibitory concentration streptomycin and obtain insights on the molecular mechanisms of the primary hit compound, respectively.

Results

Several extracts and fractions caused bacterial genome instability. Codeine, in synergy with streptomycin, regulates double-strand break (DSB) repair and causes bacterial ribosome dysfunction in the absence of DSBs, and dysregulation of ribosome biogenesis in a DSB-dependent manner.

Conclusion

This study demonstrates a potential viable strategy that we are exploring for the discovery of new chemical entities with activities against Escherichia coli and other bacterial pathogens.

Beyond Penicillin: The Potential of Filamentous Fungi for Drug Discovery in the Age of Antibiotic Resistance

Antibiotics are a staple in current medicine for the therapy of infectious diseases. However, their extensive use and misuse, combined with the high adaptability of bacteria, has dangerously increased the incidence of multi-drug-resistant (MDR) bacteria. This makes the treatment of infections challenging, especially when MDR bacteria form biofilms. The most recent antibiotics entering the market have very similar modes of action to the existing ones, so bacteria rapidly catch up to those as well. As such, it is very important to adopt effective measures to avoid the development of antibiotic resistance by pathogenic bacteria, but also to perform bioprospecting of new molecules from diverse sources to expand the arsenal of drugs that are available to fight these infectious bacteria. Filamentous fungi have a large and vastly unexplored secondary metabolome and are rich in bioactive molecules that can be potential novel antimicrobial drugs. Their production can be challenging, as the associated biosynthetic pathways may not be active under standard culture conditions. New techniques involving metabolic and genetic engineering can help boost antibiotic production. This study aims to review the bioprospection of fungi to produce new drugs to face the growing problem of MDR bacteria and biofilm-associated infections.

Genomic virulence features of Beauveria bassiana as a biocontrol agent for the mountain pine beetle population

BACKGROUND

The mountain pine beetle, Dendroctonus ponderosae, is an irruptive bark beetle that causes extensive mortality to many pine species within the forests of western North America. Driven by climate change and wildfire suppression, a recent mountain pine beetle (MPB) outbreak has spread across more than 18 million hectares, including areas to the east of the Rocky Mountains that comprise populations and species of pines not previously affected. Despite its impacts, there are few tactics available to control MPB populations. Beauveria bassiana is an entomopathogenic fungus used as a biological agent in agriculture and forestry and has potential as a management tactic for the mountain pine beetle population. This work investigates the phenotypic and genomic variation between B. bassiana strains to identify optimal strains against a specific insect.

RESULTS

Using comparative genome and transcriptome analyses of eight B. bassiana isolates, we have identified the genetic basis of virulence, which includes oosporein production. Genes unique to the more virulent strains included functions in biosynthesis of mycotoxins, membrane transporters, and transcription factors. Significant differential expression of genes related to virulence, transmembrane transport, and stress response was identified between the different strains, as well as up to nine-fold upregulation of genes involved in the biosynthesis of oosporein. Differential correlation analysis revealed transcription factors that may be involved in regulating oosporein production.

CONCLUSION

This study provides a foundation for the selection and/or engineering of the most effective strain of B. bassiana for the biological control of mountain pine beetle and other insect pests populations.

Fusarium-Derived Secondary Metabolites with Antimicrobial Effects

Fungal microbes are important in the creation of new drugs, given their unique genetic and metabolic diversity. As one of the most commonly found fungi in nature, Fusarium spp. has been well regarded as a prolific source of secondary metabolites (SMs) with diverse chemical structures and a broad spectrum of biological properties. However, little information is available concerning their derived SMs with antimicrobial effects. By extensive literature search and data analysis, as many as 185 antimicrobial natural products as SMs had been discovered from Fusarium strains by the end of 2022. This review first provides a comprehensive analysis of these substances in terms of various antimicrobial effects, including antibacterial, antifungal, antiviral, and antiparasitic. Future prospects for the efficient discovery of new bioactive SMs from Fusarium strains are also proposed.

A Close Look into the Composition and Functions of Fungal Extracellular Vesicles Produced by Phytopathogens

Fungal extracellular vesicles (EVs) were first described in human pathogens. In a few years, the field of fungal EVs evolved to include several studies with plant pathogens, in which extracellularly released vesicles play fundamental biological roles. In recent years, solid progress has been made in the determination of the composition of EVs produced by phytopathogens. In addition, EV biomarkers are now known in fungal plant pathogens, and the production of EVs during plant infection has been demonstrated. In this manuscript, we review the recent progress in the field of fungal EVs, with a focus on plant pathogens. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2023.

Extracellular vesicles in phytopathogenic fungi

Extracellular vesicles (EVs) are nano-sized lipid compartments that mediate the intercellular transport of lipids, proteins, nucleic acids and metabolites. During infectious diseases, EVs released by host cells promote immune responses, while those released by pathogens attempt to subvert host immunity. There is a growing body of research investigating the role of fungal EVs in plant pathosystems. It is becoming clear that EVs released by fungal phytopathogens play a role during infection through the transport of protein effectors, toxic metabolites and RNA. Here, we discuss recent findings on EVs in fungal phytopathogens, including the methods employed in their isolation, their characterization, contents and functionality, as well as the key questions remaining to be addressed.

Ascomycota as a source of natural colorants

In the last few decades, there has been a great demand for natural colorants. Synthetic colorants are known to be easy to produce, are less expensive, and remain stable when subjected to chemical and physical factors. In addition, only small amounts are required to color any material, and unwanted flavors and aromas are not incorporated into the product. Natural colorants present in food, in addition to providing color, also have biological properties and effects that aid in the prevention and cure of many diseases. The main classes of colorants produced by phylum Ascomycota include polyketides and carotenoids. A promising producer of colorants should be able to assimilate a variety of sources of carbon and nitrogen and also exhibit relative stability. The strain should not be pathogenic, and its product should not be toxic. Production processes should also provide the expected color with a good yield through simple extraction methods. Research that seeks new sources of these compounds should continue to seek products of biotechnological origin in order to be competitive with products of synthetic and plant origin. In this review, we will focus on the recent studies on the main producing species, classes, and metabolic pathways of colorants produced by this phylum, historical background, impact of synthetic colorants on human health and the environment, social demand for natural colorants and also an in-depth approach to bioprocesses (influences on production, optimization of bioprocess, extraction, and identification), and limitations and perspectives for the use of fungal-based dyes.

Recovery and purification of bikaverin produced by Fusarium oxysporum CCT7620

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Ethyl acetate extraction resulted in the highest bikaverin yield.

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Kinetic study revealed a saturation of bikaverin extraction after 256 min.

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Three sequential ethyl acetate extractions was the most economical to recover bikaverin.

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Open column chromatography or nanofiltration were not suitable to purify bikaverin.

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Bikaverin was successfully purified on semi-preparative HPLC.

Microbial pigments have a distinguished potential for applications in food and pharmaceutical industries, stimulating the research in this field. The present study evaluated the ideal conditions for extracting bikaverin (red pigment) from the biomass of Fusarium oxysporum CCT7620. Among the solvents tested, ethyl acetate extraction resulted in the highest bikaverin concentration and the kinetic study revealed a saturation in bikaverin concentration from 256 min on. Based on a preliminary economic study, three sequential extractions with ethyl acetate was considered the ideal protocol to recover bikaverin. After extraction, chromatographic methods were tested to purify bikaverin. The use of silica gel or Sephadex (open column) could not successfully purify bikaverin, but the semi-preparative HPLC resulted in a bikaverin-enriched fraction with a purity degree equivalent to the commercial analytical standard. This work provides relevant information regarding the extraction and purification of bikaverin, which may be useful for other downstraming processes.

Bright Side of Fusarium oxysporum: Secondary Metabolites Bioactivities and Industrial Relevance in Biotechnology and Nanotechnology

Fungi have been assured to be one of the wealthiest pools of bio-metabolites with remarkable potential for discovering new drugs. The pathogenic fungi, Fusarium oxysporum affects many valuable trees and crops all over the world, producing wilt. This fungus is a source of different enzymes that have variable industrial and biotechnological applications. Additionally, it is widely employed for the synthesis of different types of metal nanoparticles with various biotechnological, pharmaceutical, industrial, and medicinal applications. Moreover, it possesses a mysterious capacity to produce a wide array of metabolites with a broad spectrum of bioactivities such as alkaloids, jasmonates, anthranilates, cyclic peptides, cyclic depsipeptides, xanthones, quinones, and terpenoids. Therefore, this review will cover the previously reported data on F. oxysporum, especially its metabolites and their bioactivities, as well as industrial relevance in biotechnology and nanotechnology in the period from 1967 to 2021. In this work, 180 metabolites have been listed and 203 references have been cited.

Fungal quinones: diversity, producers, and applications of quinones from Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium

Quinones represent an important group of highly structurally diverse, mainly polyketide-derived secondary metabolites widely distributed among filamentous fungi. Many quinones have been reported to have important biological functions such as inhibition of bacteria or repression of the immune response in insects. Other quinones, such as ubiquinones are known to be essential molecules in cellular respiration, and many quinones are known to protect their producing organisms from exposure to sunlight. Most recently, quinones have also attracted a lot of industrial interest since their electron-donating and -accepting properties make them good candidates as electrolytes in redox flow batteries, like their often highly conjugated double bond systems make them attractive as pigments. On an industrial level, quinones are mainly synthesized from raw components in coal tar. However, the possibility of producing quinones by fungal cultivation has great prospects since fungi can often be grown in industrially scaled bioreactors, producing valuable metabolites on cheap substrates. In order to give a better overview of the secondary metabolite quinones produced by and shared between various fungi, mainly belonging to the genera Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium, this review categorizes quinones into families such as emodins, fumigatins, sorbicillinoids, yanuthones, and xanthomegnins, depending on structural similarities and information about the biosynthetic pathway from which they are derived, whenever applicable. The production of these quinone families is compared between the different genera, based on recently revised taxonomy. KEY POINTS: • Quinones represent an important group of secondary metabolites widely distributed in important fungal genera such as Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium. • Quinones are of industrial interest and can be used in pharmacology, as colorants and pigments, and as electrolytes in redox flow batteries. • Quinones are grouped into families and compared between genera according to the revised taxonomy.

Pathway engineering in yeast for synthesizing the complex polyketide bikaverin

Fungal polyketides display remarkable structural diversity and bioactivity, and therefore the biosynthesis and engineering of this large class of molecules is therapeutically significant. Here, we successfully recode, construct and characterize the biosynthetic pathway of bikaverin, a tetracyclic polyketide with antibiotic, antifungal and anticancer properties, in S. cerevisiae. We use a green fluorescent protein (GFP) mapping strategy to identify the low expression of Bik1 (polyketide synthase) as a major bottleneck step in the pathway, and a promoter exchange strategy is used to increase expression of Bik1 and bikaverin titer. Then, we use an enzyme-fusion strategy to directly couple the monooxygenase (Bik2) and methyltransferase (Bik3) to efficiently channel intermediates between modifying enzymes, leading to an improved titer of bikaverin at 202.75 mg/L with flask fermentation (273-fold higher than the initial titer). This study demonstrates that the biosynthesis of complex fungal polyketides can be established and efficiently engineered in S. cerevisiae, highlighting the potential for natural product synthesis and large-scale fermentation in yeast.

Bikaverin is a fungal-derived tetracyclic polyketide with antibiotic, antifungal and anticancer properties. Here, the authors employ various pathway engineering strategies to achieve high level production of bikaverin in baker’s yeast.

Fungal Pigments and Their Roles Associated with Human Health

Fungi can produce myriad secondary metabolites, including pigments. Some of these pigments play a positive role in human welfare while others are detrimental. This paper reviews the types and biosynthesis of fungal pigments, their relevance to human health, including their interactions with host immunity, and recent progresses in their structure-activity relationships. Fungal pigments are grouped into carotenoids, melanin, polyketides, and azaphilones, etc. These pigments are phylogenetically broadly distributed. While the biosynthetic pathways for some fungal pigments are known, the majority remain to be elucidated. Understanding the genes and metabolic pathways involved in fungal pigment synthesis is essential to genetically manipulate the production of both the types and quantities of specific pigments. A variety of fungal pigments have shown wide-spectrum biological activities, including promising pharmacophores/lead molecules to be developed into health-promoting drugs to treat cancers, cardiovascular disorders, infectious diseases, Alzheimer's diseases, and so on. In addition, the mechanistic elucidation of the interaction of fungal pigments with the host immune system provides valuable clues for fighting fungal infections. The great potential of fungal pigments have opened the avenues for academia and industries ranging from fundamental biology to pharmaceutical development, shedding light on our endeavors for disease prevention and treatment.

Genomic clustering within functionally related gene families in Ascomycota fungi

Multiple mechanisms collaborate for proper regulation of gene expression. One layer of this regulation is through the clustering of functionally related genes at discrete loci throughout the genome. This phenomenon occurs extensively throughout Ascomycota fungi and is an organizing principle for many gene families whose proteins participate in diverse molecular functions throughout the cell. Members of this phylum include organisms that serve as model systems and those of interest medically, pharmaceutically, and for industrial and biotechnological applications. In this review, we discuss the prevalence of functional clustering through a broad range of organisms within the phylum. Position effects on transcription, genomic locations of clusters, transcriptional regulation of clusters, and selective pressures contributing to the formation and maintenance of clusters are addressed, as are common methods to identify and characterize clusters.

FvatfA regulates growth, stress tolerance as well as mycotoxin and pigment productions in Fusarium verticillioides

FvatfA from the maize pathogen Fusarium verticillioides putatively encodes the Aspergillus nidulans AtfA and Schizasaccharomyces pombe Atf1 orthologous bZIP-type transcription factor, FvAtfA. In this study, a ΔFvatfA deletion mutant was constructed and then genetically complemented with the fully functional FvatfA gene. Comparing phenotypic features of the wild-type parental, the deletion mutant and the restored strains shed light on the versatile regulatory functions played by FvAtfA in (i) the maintenance of vegetative growth on Czapek-Dox and Potato Dextrose agars and invasive growth on unwounded tomato fruits, (ii) the preservation of conidiospore yield and size, (iii) the orchestration of oxidative (H₂O₂, menadione sodium bisulphite) and cell wall integrity (Congo Red) stress defences and (iv) the regulation of mycotoxin (fumonisins) and pigment (bikaverin, carotenoid) productions. Expression of selected biosynthetic genes both in the fumonisin (fum1, fum8) and the carotenoid (carRA, carB) pathways were down-regulated in the ΔFvatfA strain resulting in defected fumonisin production and considerably decreased carotenoid yields. The expression of bik1, encoding the polyketide synthase needed in bikaverin biosynthesis, was not up-regulated by the deletion of FvatfA meanwhile the ΔFvatfA strain produced approximately ten times more bikaverin than the wild-type or the genetically complemented strains. The abolishment of fumonisin production of the ΔFvatfA strain may lead to the development of new-type, biology-based mycotoxin control strategies. The novel information gained on the regulation of pigment production by this fungus can be interesting for experts working on new, Fusarium-based biomass and pigment production technologies.

Key points • FvatfA regulates vegetative and invasive growths of F. verticillioides. • FvatfA also orchestrates oxidative and cell wall integrity stress defenses. • The ΔFvatfA mutant was deficient in fumonisin production. • FvatfA deletion resulted in decreased carotenoid and increased bikaverin yields.

Profiles of fungal metabolites including regulated mycotoxins in individual dried Turkish figs by LC-MS/MS

Fungal metabolites including regulated mycotoxins were identified by a validated LC-MS/MS method in 180 individual Turkish dried figs from 2017 and 2018 harvests. Hand-selected dried figs were subjectively classified based on the extent of fluorescence. Forty-three fungal metabolites including eight EU-regulated mycotoxins were identified and quantified. Figs classified as being uncontaminated mostly did not contain aflatoxins above 1 μg/kg. Despite being "uncontaminated" from an aflatoxin perspective, kojic acid was present in significant quantities with a maximum level of 3750 mg/kg (0.375% w/w) and tenuazonic acid was also found (2 μg/kg to 298 mg/kg) in some figs. Notable in the screening of figs has been the presence of significant amounts of aflatoxin M₁ (AFM1) in figs also containing significant levels of aflatoxin B₁ (AFB1), which is the first time that AFM1 has been reported as naturally occurring in dried figs.

Coronavirus disease 2019 drug discovery through molecular docking

Background: The dawn of the year 2020 witnessed the spread of the highly infectious and communicable disease coronavirus disease 2019 (COVID-19) globally since it was first reported in 2019. Severe acute respiratory syndrome coronavirus-2 is the main causative agent. In total, 3,096,626 cases and 217,896 deaths owing to COVID-19 were reported by 30th April, 2020 by the World Health Organization. This means infection and deaths show an exponential growth globally. In order to tackle this pandemic, it is necessary to find possible easily accessible therapeutic agents till an effective vaccine is developed. Methods: In this study, we present the results of molecular docking processes through high throughput virtual screening to analyze drugs recommended for the treatment of COVID-19. Results: Atovaquone, fexofenadine acetate (Allegra), ethamidindole, baicalin, glycyrrhetic acid, justicidin D, euphol, and curine are few of the lead molecules found after docking 129 known antivirals, antimalarial, antiparasitic drugs and 992 natural products. Conclusions: These molecules could act as an effective inhibitory drug against COVID-19.

Modeling bikaverin production by Fusarium oxysporum CCT7620 in shake flask cultures

Bikaverin is a fungal red pigment that presents antimicrobial and antitumor activities. Therefore, this substance could be used as an alternative additive in the food and pharmaceutical industries. The aim of this work was to use response surface methodology to optimize the fermentation conditions and maximize the production of bikaverin in shake flasks. The variables investigated were agitation speed (71–289 rpm), temperature (21–35 °C), and substrate (rice) concentration in the culture medium (16.4–83.6 g/L). The agitation speed had a positive effect on red pigment production, while substrate concentration and temperature had the opposite effect. Maximum bikaverin production was predicted to occur using 289 rpm, 24.3 °C, and 16.4 g/L rice concentration. Experimental validation using 289 rpm, 28 °C, and 20 g/L rice concentration was 6.2% higher than predicted by the model. The present investigation was important for defining the best conditions for the production of bikaverin.

Putative metabolic pathway for the bioproduction of bikaverin and intermediates thereof in the wild Fusarium oxysporum LCP531 strain

Fungal naphthoquinones, like red bikaverin, are of interest due to their growing applications in designing pharmaceutical products. Though considerable work has been done on the elucidation of bikaverin biosynthesis pathway in Fusarium fujikuroi, very few reports are available regarding its bioproduction in F. oxysporum. We are hereby proposing a putative metabolic pathway for bikaverin bioproduction in a wild F. oxysporum strain by cross-linking the pigment profiles we obtained under two different fermentation conditions with literature. Naphthoquinone pigments were extracted with a pressurized liquid extraction method, and characterized by HPLC–DAD and UHPLC-HRMS. The results led to the conclusions that the F. oxysporum LCP531 strain was able to produce bikaverin and its various intermediates, e.g., pre-bikaverin, oxo-pre-bikaverin, dinor-bikaverin, me-oxo-pre-bikaverin, and nor-bikaverin, in submerged cultures in various proportions. To our knowledge, this is the first report of the isolation of these five bikaverin intermediates from F. oxysporum cultures, providing us with steady clues for confirming a bikaverin metabolic pathway as well as some of its regulatory patterns in the F. oxysporum LCP531 strain, based on the previously reported model in F. fujikuroi. Interestingly, norbikaverin accumulated along with bikaverin in mycelial cells when the strain grew on simple carbon and nitrogen sources and additional cofactors. Along bikaverin production, we were able to describe the excretion of the toxin beauvericin as main extrolite exclusively in liquid medium containing complex nitrogen and carbon sources, as well as the isolation of ergosterol derivate in mycelial extracts, which have potential for pharmaceutical uses. Therefore, culture conditions were also concluded to trigger some specific biosynthetic route favoring various metabolites of interest. Such observation is of great significance for selective production of pigments and/or prevention of occurrence of others (aka mycotoxins).

Twenty-Eight Fungal Secondary Metabolites Detected in Pig Feed Samples: Their Occurrence, Relevance and Cytotoxic Effects In Vitro

Feed samples are frequently contaminated by a wide range of chemically diverse natural products, which can be determined using highly sensitive analytical techniques. Next to already well-investigated mycotoxins, unknown or unregulated fungal secondary metabolites have also been found, some of which at significant concentrations. In our study, 1141 pig feed samples were analyzed for more than 800 secondary fungal metabolites using the same LC-MS/MS method and ranked according to their prevalence. Effects on the viability of the 28 most relevant were tested on an intestinal porcine epithelial cell line (IPEC-J2). The most frequently occurring compounds were determined as being cyclo-(L-Pro-L-Tyr), moniliformin, and enniatin B, followed by enniatin B1, aurofusarin, culmorin, and enniatin A1. The main mycotoxins, deoxynivalenol and zearalenone, were found only at ranks 8 and 10. Regarding cytotoxicity, apicidin, gliotoxin, bikaverin, and beauvericin led to lower IC50 values, between 0.52 and 2.43 µM, compared to deoxynivalenol (IC50 = 2.55 µM). Significant cytotoxic effects were also seen for the group of enniatins, which occurred in up to 82.2% of the feed samples. Our study gives an overall insight into the amount of fungal secondary metabolites found in pig feed samples compared to their cytotoxic effects in vitro.

Biosynthesis of Jasmonates from Linoleic Acid by the Fungus Fusarium oxysporum. Evidence for a Novel Allene Oxide Cyclase

Fusarium oxysporum f. sp. tulipae (FOT) secretes (+)-7-iso-jasmonoyl-(S)-isoleucine ((+)-JA-Ile) to the growth medium together with about 10 times less 9,10-dihydro-(+)-7-iso-JA-Ile. Plants and fungi form (+)-JA-Ile from 18:3n-3 via 12-oxophytodienoic acid (12-OPDA), which is formed sequentially by 13S-lipoxygenase, allene oxide synthase (AOS), and allene oxide cyclase (AOC). Plant AOC does not accept linoleic acid (18:2n-6)-derived allene oxides and dihydrojasmonates are not commonly found in plants. This raises the question whether 18:2n-6 serves as the precursor of 9,10-dihydro-JA-Ile in Fusarium, or whether the latter arises by a putative reductase activity operating on the n-3 double bond of (+)-JA-Ile or one of its precursors. Incubation of pentadeuterated (d₅ ) 18:3n-3 with mycelia led to the formation of d₅ -(+)-JA-Ile whereas d₅ -9,10-dihydro-JA-Ile was not detectable. In contrast, d₅ -9,10-dihydro-(+)-JA-Ile was produced following incubation of [17,17,18,18,18-² H₅ ]linoleic acid (d₅ -18:2n-6). Furthermore, 9(S),13(S)-12-oxophytoenoic acid, the 15,16-dihydro analog of 12-OPDA, was formed upon incubation of unlabeled or d₅ -18:2n-6. Appearance of the α-ketol, 12-oxo-13-hydroxy-9-octadecenoic acid following incubation of unlabeled or [¹³ C₁₈ ]-labeled 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoic acid confirmed the involvement of AOS and the biosynthesis of the allene oxide 12,13(S)-epoxy-9,11-octadecadienoic acid. The lack of conversion of this allene oxide by AOC in higher plants necessitates the conclusion that the fungal AOC is distinct from the corresponding plant enzyme.

In Vitro and in Silico Evaluation of Bikaverin as a Potent Inhibitor of Human Protein Kinase CK2

Protein kinase CK2 is an emerging target for therapeutic intervention in human diseases, particularly in cancer. Inhibitors of this enzyme are currently in clinical trials, indicating the druggability of human CK2. By virtual screening of the ZINC database, we found that the natural compound bikaverin can fit well in the ATP binding site of the target enzyme CK2. By further in vitro evaluation using CK2 holoenzyme, bikaverin turned to be a potent inhibitor with an IC₅₀ value of 1.24 µM. In this work, the cell permeability of bikaverin was determined using a Caco-2 cell permeability assay as a prerequisite for cellular evaluation and the compound turned out to be cell permeable with a P_app- value of 4.46 × 10^-6 cm/s. Bikaverin was tested for its effect on cell viability using a MTT assay and cell proliferation using an EdU assay in different cancer cell lines (MCF7, A427 and A431 cells). Cell viability and cell proliferation were reduced dramatically after treatment with 10 µM bikaverin for 24 h. Additionally the IncuCyte^® live-cell imaging system was applied for monitoring the cytotoxicity of bikaverin in the three tested cancer cell lines. Finally, molecular dynamic studies were performed to clarify the ligand binding mode of bikaverin at the ATP binding site of CK2 and to identify the amino acids involved.

Metabolic profiling of Fusarium oxysporum f. sp. conglutinans race 2 in dual cultures with biocontrol agents Bacillus amyloliquefaciens, Pseudomonas aeruginosa, and Trichoderma harzianum

There are increasing efforts to identify biocontrol-active microbial metabolites in order to improve strategies for biocontrol of phytopathogens. In this work, Fusarium oxysporum f. sp. conglutinans was confronted with three different biocontrol agents: Trichoderma harzianum, Bacillus amyloliquefaciens, and Pseudomonas aeruginosa in dual culture bioassays. Metabolites produced during the microbial interactions were screened by a matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). T. harzianum exhibited the strongest inhibition of growth of F. oxysporum resulting in overlay of the pathogen colony with its mycelium. Recorded metabolite profiles suggested a direct attack of F. oxysporum mycelium by T. harzianum and B. amyloliquefaciens by means of membrane-attacking peptaibols and a set of antimicrobial lipopeptides and siderophores, respectively. The direct mode of the biocontrol activity of T. harzianum and B. amyloliquefaciens corresponded to their ability to suppress F. oxysporum production of mycotoxin beauvericin suggesting that this ability is not specific only for Trichoderma species. In the case of P. aeruginosa, siderophores pyoverdine E/D and two rhamnolipids were produced as major bacterial metabolites; the rhamnolipid production was blocked by F. oxysporum. The results showed that this type of biocontrol activity was the least effective against F. oxysporum. The effective application of MALDI-MS profiling to the screening of nonvolatile microbial metabolites produced during the interaction of the phytopathogen and the biocontrol microorganisms was demonstrated.

Induction of pigment production through media composition, abiotic and biotic factors in two filamentous fungi

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Pigment production and accumulation is dependent of high C:N ratios in F. oxysporum and A. chevaleri.

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Red pigment content of F. oxysporum in terms of Absorbance units per gram of biomass increased in 191% through use of blue light. Different light wavelengths stimulate synthesis of additional pigments in A. chevalieri with highest accumulation in red and UV-light.

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Stimulation of pigment production in co-culture is species – specific, being only accomplished in A. chevalieri. With a rise higher that 500% of a pigment obtained in green light.

In addition to plant-derived, fungal pigments have become an alternative in respect to synthetic ones. Besides Monascus sp., several pigment-producing fungi do not have culture conditions well-established yet. In this research, media composition, light wavelength and co-culture were evaluated, results were reported in Absorbance Units per gram of biomass (AU/Bgr). For Fusarium oxysporum a C:N ratio above 7 was advantageous, using both complex and defined media; blue LED light increased the AU/Bgr value from 18013 to 344; co-culture did not enhance pigment production. In Aspergillus chevalieri a high C:N ratio with glucose as carbon source was ideal. When exposing cultures to light, UV and red light gave the highest pigmentation; moreover, differential UV-VIS spectra in all wavelengths suggested production of additional pigments. Particularly a pigment observed when cultured in green light was also found in co-culture with yeast and there was an improvement of AU/Bgr value of 52549%. This is the first report regarding light effect and co-culture for these fungi, as well as C:N ratio for A. chevalieri.

Extracellular Vesicles From the Cotton Pathogen Fusarium oxysporum f. sp. vasinfectum Induce a Phytotoxic Response in Plants

Extracellular vesicles (EVs) represent a system for the coordinated secretion of a variety of molecular cargo including proteins, lipids, nucleic acids, and metabolites. They have an essential role in intercellular communication in multicellular organisms and have more recently been implicated in host-pathogen interactions. Study of the role for EVs in fungal biology has focused on pathogenic yeasts that are major pathogens in humans. In this study we have expanded the investigation of fungal EVs to plant pathogens, specifically the major cotton pathogen Fusarium oxysporum f. sp. vasinfectum. EVs isolated from F. oxysporum f. sp. vasinfectum culture medium have a morphology and size distribution similar to EVs from yeasts such as Candida albicans and Cryptococcus neoformans. A unique feature of the EVs from F. oxysporum f. sp. vasinfectum is their purple color, which is predicted to arise from a napthoquinone pigment being packaged into the EVs. Proteomic analysis of F. oxysporum f. sp. vasinfectum EVs revealed that they are enriched in proteins that function in synthesis of polyketides as well as proteases and proteins that function in basic cellular processes. Infiltration of F. oxysporum f. sp. vasinfectum EVs into the leaves of cotton or N. benthamiana plants led to a phytotoxic response. These observations lead to the hypothesis that F. oxysporum f. sp. vasinfectum EVs are likely to play a crucial role in the infection process.

Conserved Responses in a War of Small Molecules between a Plant-Pathogenic Bacterium and Fungi

Small-molecule signaling is one major mode of communication within the polymicrobial consortium of soil and rhizosphere. While microbial secondary metabolite (SM) production and responses of individual species have been studied extensively, little is known about potentially conserved roles of SM signals in multilayered symbiotic or antagonistic relationships. Here, we characterize the SM-mediated interaction between the plant-pathogenic bacterium Ralstonia solanacearum and the two plant-pathogenic fungi Fusarium fujikuroi and Botrytis cinerea We show that cellular differentiation and SM biosynthesis in F. fujikuroi are induced by the bacterially produced lipopeptide ralsolamycin (synonym ralstonin A). In particular, fungal bikaverin production is induced and preferentially accumulates in fungal survival spores (chlamydospores) only when exposed to supernatants of ralsolamycin-producing strains of R. solanacearum Although inactivation of bikaverin biosynthesis moderately increases chlamydospore invasion by R. solanacearum, we show that other metabolites such as beauvericin are also induced by ralsolamycin and contribute to suppression of R. solanacearum growth in vitro Based on our findings that bikaverin antagonizes R. solanacearum and that ralsolamycin induces bikaverin biosynthesis in F. fujikuroi, we asked whether other bikaverin-producing fungi show similar responses to ralsolamycin. Examining a strain of B. cinerea that horizontally acquired the bikaverin gene cluster from Fusarium, we found that ralsolamycin induced bikaverin biosynthesis in this fungus. Our results suggest that conservation of microbial SM responses across distantly related fungi may arise from horizontal transfer of protective gene clusters that are activated by conserved regulatory cues, e.g., a bacterial lipopeptide, providing consistent fitness advantages in dynamic polymicrobial networks.IMPORTANCE Bacteria and fungi are ubiquitous neighbors in many environments, including the rhizosphere. Many of these organisms are notorious as economically devastating plant pathogens, but little is known about how they communicate chemically with each other. Here, we uncover a conserved antagonistic communication between the widespread bacterial wilt pathogen Ralstonia solanacearum and plant-pathogenic fungi from disparate genera, Fusarium and Botrytis Exposure of Fusarium fujikuroi to the bacterial lipopeptide ralsolamycin resulted in production of the antibacterial metabolite bikaverin specifically in fungal tissues invaded by Ralstonia Remarkably, ralsolamycin induction of bikaverin was conserved in a Botrytis cinerea isolate carrying a horizontally transferred bikaverin gene cluster. These results indicate that horizontally transferred gene clusters may carry regulatory prompts that contribute to conserved fitness functions in polymicrobial environments.

MYB72-dependent coumarin exudation shapes root microbiome assembly to promote plant health

Plant roots nurture a large diversity of soil microbes via exudation of chemical compounds into the rhizosphere. In turn, beneficial root microbiota promote plant growth and immunity. The root-specific transcription factor MYB72 has emerged as a central regulator in this process. Here, we show that MYB72 regulates the excretion of the coumarin scopoletin, an iron-mobilizing phenolic compound with selective antimicrobial activity that shapes the root-associated microbial community. Selected soil-borne fungal pathogens appeared to be highly sensitive to the antimicrobial activity of scopoletin, while two MYB72-inducing beneficial rhizobacteria were tolerant. Our results suggest that probiotic root-associated microbes that activate the iron-deficiency response during colonization stimulate MYB72-dependent excretion of scopoletin, thereby potentially improving their niche establishment and enhancing plant growth and protection.

Plant roots nurture a tremendous diversity of microbes via exudation of photosynthetically fixed carbon sources. In turn, probiotic members of the root microbiome promote plant growth and protect the host plant against pathogens and pests. In the Arabidopsis thaliana–Pseudomonas simiae WCS417 model system the root-specific transcription factor MYB72 and the MYB72-controlled β-glucosidase BGLU42 emerged as important regulators of beneficial rhizobacteria-induced systemic resistance (ISR) and iron-uptake responses. MYB72 regulates the biosynthesis of iron-mobilizing fluorescent phenolic compounds, after which BGLU42 activity is required for their excretion into the rhizosphere. Metabolite fingerprinting revealed the antimicrobial coumarin scopoletin as a dominant metabolite that is produced in the roots and excreted into the rhizosphere in a MYB72- and BGLU42-dependent manner. Shotgun-metagenome sequencing of root-associated microbiota of Col-0, myb72, and the scopoletin biosynthesis mutant f6′h1 showed that scopoletin selectively impacts the assembly of the microbial community in the rhizosphere. We show that scopoletin selectively inhibits the soil-borne fungal pathogens Fusarium oxysporum and Verticillium dahliae, while the growth-promoting and ISR-inducing rhizobacteria P. simiae WCS417 and Pseudomonas capeferrum WCS358 are highly tolerant of the antimicrobial effect of scopoletin. Collectively, our results demonstrate a role for coumarins in microbiome assembly and point to a scenario in which plants and probiotic rhizobacteria join forces to trigger MYB72/BGLU42-dependent scopolin production and scopoletin excretion, resulting in improved niche establishment for the microbial partner and growth and immunity benefits for the host plant.

Characterization of a red pigment from Fusarium chlamydosporum exhibiting selective cytotoxicity against human breast cancer MCF-7 cell lines

AIM

This research aims to characterize the pigment produced by isolated fungi and to evaluate its anticancer activities.

METHODS AND RESULTS

Pigment-producing fungi was isolated and identified as Fusarium chlamydosporum. The pigment was extracted with chloroform, purified by preparative TLC and characterized by Fourier transmittance infrared, electron spray ionization mass spectroscopy, liquid chromatography mass spectroscopy and nuclear magnetic resonance (NMR) (¹ HNMR, ¹³ C NMR) spectral analysis, which revealed the pigment to be 'long chain hydrocarbons with poly unsaturated groups' (m/z 702). Pigment stability varied with different pH, temperature and sunlight conditions. The pigment-induced cell death in human breast adenocarcinoma cells MCF-7 and showed no significant toxicity in CHOK 1 cells. Lipid peroxidation assay revealed that treatment with pigment was able to reduce the lipid peroxidation caused by H₂ O₂ in MCF-7 cells.

CONCLUSIONS

The F. chlamydosporum pigment is a compound of long-chain hydrocarbons with poly unsaturated groups, possessing selective cytotoxicity in MCF-7 cancer cell lines.

SIGNIFICANCE AND IMPACT OF THE STUDY

The pigment can be used as a colouring agent in cosmetics. Its anticancer potential can be used in production of therapeutics in increasing demand cancer research.

Antifungal Activity and Action Mode of Cuminic Acid from the Seeds of Cuminum cyminum L. against Fusarium oxysporum f. sp. Niveum (FON) Causing Fusarium Wilt on Watermelon

In order to develop a novel biofungicide, the antifungal activity and action mode of cuminic acid from the seed of Cuminum cyminum L. against Fusarium oxysporum f. sp. niveum (FON) on watermelon was determined systematically. In this study, the median effective concentration (EC50) value for cuminic acid in inhibiting mycelial growth of FON was 22.53 μg/mL. After treatment with cuminic acid, the mycelial morphology was seriously influenced; cell membrane permeability and glycerol content were increased markedly, but pigment and mycotoxin (mainly fusaric acid) were significantly decreased. Synthesis genes of bikaverin (Bike1, Bike2 and Bike3) and fusaric acid (FUB1, FUB2, FUB3 and FUB4) both were downregulated compared with the control, as confirmed by quantitative RT-PCR. In greenhouse experiments, cuminic acid at all concentrations displayed significant bioactivities against FON. Importantly, significant enhancement of activities of SOD, POD, CAT and decrease of MDA content were observed after in vivo cuminic acid treatment on watermelon leaves. These indicated that cuminic acid not only showed high antifungal activity, but also could enhance the self-defense system of the host plant. Above all, cuminic acid showed the potential as a biofungicide to control FON.

Production and New Extraction Method of Polyketide Red Pigments Produced by Ascomycetous Fungi from Terrestrial and Marine Habitats

The use of ascomycetous fungi as pigment producers opens the way to an alternative to synthetic dyes, especially in the red-dye industries, which have very few natural pigment alternatives. The present paper aimed to bio-prospect and screen out 15 selected ascomycetous fungal strains, originating from terrestrial and marine habitats belonging to seven different genera (Penicillium, Talaromyces, Fusarium, Aspergillus, Trichoderma, Dreschlera, and Paecilomyces). We identified four strains, Penicillium purpurogenum rubisclerotium, Fusarium oxysporum, marine strains identified as Talaromyces spp., and Trichoderma atroviride, as potential red pigment producers. The extraction of the pigments is a crucial step, whereby the qualitative and quantitative compositions of each fungal extract need to be respected for reliable identification, as well as preserving bioactivity. Furthermore, there is a growing demand for more sustainable and cost-effective extraction methods. Therefore, a pressurized liquid extraction technique was carried out in this study, allowing a greener and faster extraction step of the pigments, while preserving their chemical structures and bioactivities in comparison to conventional extraction processes. The protocol was illustrated with the production of pigment extracts from P. purpurogenum rubisclerotium and Talaromyces spp. Extracts were analyzed by high-performance liquid-chromatography combined with photodiode array-detection (HPLC-DAD) and high-resolution mass spectrometry (UHPLC-HRMS). The more promising strain was the isolate Talaromyces spp. of marine origin. The main polyketide pigment produced by this strain has been characterized as N-threoninerubropunctamine, a non-toxic red Monascus-like azaphilone pigment.

Potential of Burkholderia seminalis TC3.4.2R3 as Biocontrol Agent Against Fusarium oxysporum Evaluated by Mass Spectrometry Imaging

Species of genus Burkholderia display different interaction profiles in the environment, causing either several diseases in plants and animals or being beneficial to some plants, promoting their growth, and suppressing phytopathogens. Burkholderia spp. also produce many types of biomolecules with antimicrobial activity, which may be commercially used to protect crops of economic interest, mainly against fungal diseases. Herein we have applied matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to investigate secondary metabolites produced by B. seminalis TC3.4.2R3 in monoculture and coculture with plant pathogen Fusarium oxysporum. The siderophore pyochelin and the rhamnolipid Rha-Rha-C15-C14 were detected in wild-type B. seminalis strain, and their productions were found to vary in mutant strains carrying disruptions in gene clusters associated with antimicrobial compounds. Two mycotoxins were detected in F. oxysporum. During coculture with B. seminalis, metabolites probably related to defense mechanisms of these microorganisms were observed in the interspecies interaction zone. Our findings demonstrate the effective application of MALDI-MSI in the detection of bioactive molecules involved in the defense mechanism of B. seminalis, and these findings suggest the potential use of this bacterium in the biocontrol of plant diseases caused by F. oxysporum. Graphical Abstract ᅟ.

Development of Pharmacophore Model for Indeno[1,2-b]indoles as Human Protein Kinase CK2 Inhibitors and Database Mining

Protein kinase CK2, initially designated as casein kinase 2, is an ubiquitously expressed serine/threonine kinase. This enzyme, implicated in many cellular processes, is highly expressed and active in many tumor cells. A large number of compounds has been developed as inhibitors comprising different backbones. Beside others, structures with an indeno[1,2-b]indole scaffold turned out to be potent new leads. With the aim of developing new inhibitors of human protein kinase CK2, we report here on the generation of common feature pharmacophore model to further explain the binding requirements for human CK2 inhibitors. Nine common chemical features of indeno[1,2-b]indole-type CK2 inhibitors were determined using MOE software (Chemical Computing Group, Montreal, Canada). This pharmacophore model was used for database mining with the aim to identify novel scaffolds for developing new potent and selective CK2 inhibitors. Using this strategy several structures were selected by searching inside the ZINC compound database. One of the selected compounds was bikaverin (6,11-dihydroxy-3,8-dimethoxy-1-methylbenzo[b]xanthene-7,10,12-trione), a natural compound which is produced by several kinds of fungi. This compound was tested on human recombinant CK2 and turned out to be an active inhibitor with an IC₅₀ value of 1.24 µM.

Production of bikaverin by a Fusarium fujikuroi mutant in submerged cultures

A variety of mutants having different colony characteristics, morphology and soluble pigmentation were generated from Fusarium fujikuroi by exposure to UV radiation. Mutants were selected that formed dry, compact, small colonies with reddish-violet pigment on regeneration agar plates. The production of bikaverin by Mut-4 was examined in shake flasks in media with different nitrogen and carbon sources. The optimal C: N ratio for the maximal bikaverin production by Mut-4 was 150:1. It produced still higher bikaverin (6.3 g l(-1)) in a medium containing defatted cottonseed meal as nitrogen source, in combination with glucose. Bikaverin produced was extracted, purified and characterized by UV-visible and NMR spectroscopy. Bikaverin production in the present investigation was substantially higher than that reported by earlier investigators in submerged and solid-state fermentations.

Bacillus mojavensis RRC101 Lipopeptides Provoke Physiological and Metabolic Changes During Antagonism Against Fusarium verticilliodes

The mycotoxigenic pathogen Fusarium verticillioides threatens the quality and utility of maize across industrial and agricultural purposes. Chemical control is complicated by the intimate endophytic lifestyle of the pathogen with its host. Bacillus mojavensis RRC101, a maize-endophytic bacterium, has been observed to reduce F. verticillioides disease severity and fumonisin accumulation when coinoculated to maize. Genome sequencing and annotation identified a number of biocontrol-relevant pathways in RRC101. Biochemical assays confirmed the presence and activity of surfactin- and fengycin-type lipopeptides, with fengycins responsible for antifungal activity against F. verticillioides. This antagonism manifests as inhibition of filamentous growth, with microscopy revealing hyphal distortions, vacuolization, and lysis. F. verticillioides secondary metabolism also responds to antagonism, with lipopeptide challenge inducing greater fumonisin production and, in the case of fengycins, eliciting pigment accumulation at sites of inhibition. Together, these data suggest that antibiotic and toxin production are components of a complex biochemical interaction among maize endophytes, one pathogenic and one beneficial.

Transporter and its engineering for secondary metabolites

Secondary metabolites possess a lot of biological activities, and to achieve their functions, transmembrane transportation is crucial. Elucidation of their transport mechanisms in the cell is critical for discovering ways to improve the production. Here, we have summarized the recent progresses for representative secondary metabolite transporters and also the strategies for uncovering the transporter systems in plants and microbes. We have also discussed the transporter engineering strategies being utilized for improving the heterologous natural product production, which exhibits promising future under the guide of synthetic biology.

Comparative proteomic analyses reveal that Gnt2-mediated N-glycosylation affects cell wall glycans and protein content in Fusarium oxysporum

Protein N-glycosylation is a ubiquitous post-translational modification that contributes to appropriate protein folding, stability, functionality and localization. N-glycosylation has been identified as an important process for morphogenesis and virulence in several fungal pathogens including Fusarium oxysporum. Here we conducted comparative chemical and proteome-based analyses to better understand the physiological changes associated with protein hypo-N-glycosylation in F. oxysporum N-glycosyltransferase Gnt2-deficient mutant. The results suggest that lack of functional Gnt2 alters the size of galactofuranose chains in cell wall glycans, resulting in polysaccharides with a broad range of polymerization degrees and differential protein glycosylation patterns. Functional Gnt2 is necessary for normal conidium size and morphology and wild-type hyphal fusion rates. Hypo-N-glycosylation in ∆gnt2 mutant results in enhanced oxidative stress resistance and reduced levels of proteins involved in cell wall organization, biogenesis and remodelling. Deletion of gnt2 gene led to accumulation of trafficking vesicles at hyphal tips, reduced secretion of extracellular proteins related to detoxification of antifungal compounds and degradation of plant cell walls, and lowered extracellular polygalacturonase activity. Altogether, the results confirm that Gnt2-mediated N-glycosylation plays a crucial role in morphogenesis and virulence, and demonstrate that Gnt2 is essential for protein function, transport and relative abundance in F. oxysporum.

Factors Influencing Production of Fusaristatin A in Fusarium graminearum

Fusarium graminearum is a ubiquitous plant pathogen, which is able to produce several bioactive secondary metabolites. Recently, the cyclic lipopeptide fusaristatin A was isolated from this species and the biosynthetic gene cluster identified. Fusaristatin A consists of a C₂₄ reduced polyketide and the three amino acids dehydroalanine, β-aminoisobutyric acid and glutamine and is biosynthesized by a collaboration of a polyketide synthase and a nonribosomal peptide synthetase. To gain insight into the environmental factors, which controls the production of fusaristatin A, we cultivated F. graminearum under various conditions. We developed an LC-MS/MS method to quantify fusaristatin A in F. graminearum extracts. The results showed that yeast extract sucrose (YES) medium was the best medium for fusaristatin A production and that the optimal pH was 7.5 and temperature 25–30 °C. Furthermore, production of fusaristatin A was more than four times higher in stationary cultures than in agitated cultures when F. graminearum was grown in liquid YES medium. The results also showed that fusaristatin A was only present in the mycelium and not in the liquid, which suggests that fusaristatin A is stored intracellulally and not exported to the extracellular environment.

Neuroprotective effects of bikaverin on H2O2-induced oxidative stress mediated neuronal damage in SH-SY5Y cell line

The generation of free radicals and oxidative stress has been linked to several neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, Huntington's disease, and Amyotrophic lateral sclerosis. The use of free radical scavenging molecules for the reduction of intracellular reactive oxygen species is one of the strategies used in the clinical management of neurodegeneration. Fungal secondary metabolism is a rich source of novel molecules with potential bioactivity. In the current study, bikaverin was extracted from Fusarium oxysporum f. sp. lycopersici and its structural characterization was carried out. Further, we explored the protective effects of bikaverin on oxidative stress and its anti-apoptotic mechanism to attenuate H2O2-induced neurotoxicity using human neuroblastoma SH-SY5Y cells. Our results elucidate that pretreatment of neurons with bikaverin attenuates the mitochondrial and plasma membrane damage induced by 100 µM H2O2 to 82 and 26% as evidenced by MTT and LDH assays. H2O2 induced depletion of antioxidant enzyme status was also replenished by bikaverin which was confirmed by Realtime Quantitative PCR analysis of SOD and CAT genes. Bikaverin pretreatment efficiently potentiated the H2O2-induced neuronal markers, such as BDNF, TH, and AADC expression, which orchestrate the neuronal damage of the cell. The H2O2-induced damage to cells, nuclear, and mitochondrial integrity was also restored by bikaverin. Bikaverin could be developed as a preventive agent against neurodegeneration and as an alternative to some of the toxic synthetic antioxidants.

The gene cutA of Fusarium fujikuroi, encoding a protein of the haloacid dehalogenase family, is involved in osmotic stress and glycerol metabolism

Survival of micro-organisms in natural habitats depends on their ability to adapt to variations in osmotic conditions. We previously described the gene cut-1 of Neurospora crassa, encoding a protein of the haloacid dehalogenase family with an unknown function in the osmotic stress response. Here we report on the functional analysis of cutA, the orthologous gene in the phytopathogenic fungus Fusarium fujikuroi. cutA mRNA levels increased transiently after exposure to 0.68 M NaCl and were reduced upon return to normal osmotic conditions; deletion of the gene resulted in a partial reduction in tolerance to osmotic stress. ΔcutA mutants contained much lower intracellular levels of glycerol than the wild-type, and did not exhibit the increase following hyper-osmotic shock expected from the high osmolarity glycerol (HOG) response. cutA is linked and divergently transcribed with the putative glycerol dehydrogenase gene gldB, which showed the same regulation by osmotic shock. The intergenic cutA/gldB regulatory region contains putative stress-response elements conserved in other fungi, and both genes shared other regulatory features, such as induction by heat shock and by illumination. Photoinduction was also observed in the HOG response gene hogA, and was lost in mutants of the white collar gene wcoA. Previous data on glycerol production in Aspergillus spp. and features of the predicted CutA protein lead us to propose that F. fujikuroi produces glycerol from dihydroxyacetone, and that CutA is the enzyme involved in the synthesis of this precursor by dephosphorylation of dihydroxyacetone-3P.