The distribution of 3-hydroxy oxylipins in fungi

Characterization of linoleate dioxygenases in basidiomycetes and the functional role of CcLdo1 in regulating fruiting body development in Coprinopsis cinerea

Coprinopsis cinerea, a model fungus, is utilized for investigating the developmental mechanisms of basidiomycetes. The development of basidiomycetes is a highly organized process that requires coordination among genetic, environmental, and physiological factors. Oxylipins, a class of widely distributed signaling molecules, play crucial roles in fungal biology. Among oxylipins, the sexual pheromone-inducing factors (psi factors) have been identified as key regulators of the balance between asexual and sexual spore development in Ascomycetes. Linoleate dioxygenases are enzymes involved in the biosynthesis of psi factors, yet their specific physiological functions in basidiomycete development remain unclear. In this study, linoleate dioxygenases in basidiomycetes were identified and characterized. Phylogenetic analysis revealed that linoleate dioxygenases from Basidiomycota formed a distinct clade, with linoleate dioxygenases from Agaricomycetes segregating into three groups and those from Ustilaginomycetes forming a separate group. Both basidiomycete and ascomycete linoleate dioxygenases shared two characteristic domains: the N-terminal of linoleate dioxygenase domain and the C-terminal of cytochrome P450 domain. While the linoleate dioxygenase domains exhibited similarity between basidiomycetes and ascomycetes, the cytochrome P450 domains displayed high diversity in key sites. Furthermore, the gene encoding the linoleate dioxygenase Ccldo1 in C. cinerea was knocked out, resulting in a significant increase in fruiting body formation without affecting asexual conidia production. This observation suggests that secondary metabolites synthesized by CcLdo1 negatively regulate the sexual reproduction process in C. cinerea while not influencing the asexual reproductive process. This study represents the first identification of a gene involved in secondary metabolite synthesis that regulates basidiocarp development in a basidiomycete.

What can be lost? Genomic perspective on the lipid metabolism of Mucoromycota

Mucoromycota is a phylum of early diverging fungal (EDF) lineages, of mostly plant-associated terrestrial fungi. Some strains have been selected as promising biotechnological organisms due to their ability to produce polyunsaturated fatty acids and efficient conversion of nutrients into lipids. Others get their lipids from the host plant and are unable to produce even the essential ones on their own. Following the advancement in EDF genome sequencing, we carried out a systematic survey of lipid metabolism protein families across different EDF lineages. This enabled us to explore the genomic basis of the previously documented ability to produce several types of lipids within the fungal tree of life. The core lipid metabolism genes showed no significant diversity in distribution, however specialized lipid metabolic pathways differed in this regard among different fungal lineages. In total 165 out of 202 genes involved in lipid metabolism were present in all tested fungal lineages, while remaining 37 genes were found to be absent in some of fungal lineages. Duplications were observed for 69 genes. For the first time we demonstrate that ergosterol is not being produced by several independent groups of plant-associated fungi due to the losses of different ERG genes. Instead, they possess an ancestral pathway leading to the synthesis of cholesterol, which is absent in other fungal lineages. The lack of diacylglycerol kinase in both Mortierellomycotina and Blastocladiomycota opens the question on sterol equilibrium regulation in these organisms. Early diverging fungi retained most of beta oxidation components common with animals including Nudt7, Nudt12 and Nudt19 pointing at peroxisome divergence in Dikarya. Finally, Glomeromycotina and Mortierellomycotina representatives have a similar set of desaturases and elongases related to the synthesis of complex, polyunsaturated fatty acids pointing at an ancient expansion of fatty acid metabolism currently being explored by biotechnological studies.

Multi-omics eco-surveillance of bacterial community function in legacy contaminated estuary sediments

Complex legacy contamination is a major issue for many estuaries, with toxicity affecting change in bacterial communities, and their provision of associated goods and services. Sequencing surveys of bacterial community composition provide inferred function; however, additional insights may be generated by measurement of realised metabolic phenotypes. We apply multi-omics (genomics, lipidomics, and metabolomics), with traditional sediment quality analyses, to characterise sediment-associated bacterial communities in an estuary subject to legacy metal contamination (Zn, Hg, As, Cd, Cu and Pb). Analyses of bacterial composition and inferred function (genomics) are coupled with measurements of realised bacterial phenotype (metabolomics and lipidomics) at multiple industrialised and reference sites. At sites with the highest sediment metal concentrations (NTB), we also observed increased abundances of hydrocarbon and sulphuric acid metabolites, indicating additional sediment contamination. Bacterial phyla across sampled sites were dominated by Proteobacteria and Desulfobacteria. NTB sites were enriched with metabolically versatile, cooperative and biofilm forming phyla including, Zixibacteria, Spirochaetota, SAR324 clade, Proteobacteria, Latescibacterota, Desulfobacterota, Deferrisomtota and Acidobateriota; with inferred functions characterised by sulphur metabolism, pathways associated with the degradation of complex organic molecules, and fermentation. Reference sites were characterised by enhanced vitamin biosynthesis, cell wall, cofactor and carbohydrate biosynthesis, and CO₂ fixation. Measured metabolic phenotypes at NTB sites supported predicted functions, with most consistent change observed to naphthalene and aminobenzoate degradation pathways and carbohydrate metabolism (galactose, amino and nucleotide sugar). Change in NTB metabolite profiles was most highly correlated with sediment Hg concentrations, indicative of toxic exposure and potential for Hg methylation. Lipid profiles generated further insight into potential functional (hydroxy fatty acids) and community level change (ceramide phosphoethanolamines, unsaturated glycerides). Multi-omics outputs provided insights into bacterial community functions, modes of contaminant toxicity and expressed mechanisms of adaptation, necessary to better inform management decisions and predictive models in increasingly human-influenced environments.

Pioneering Metabolomic Studies on Diaporthe eres Species Complex from Fruit Trees in the South-Eastern Poland

Fungi from the genus Diaporthe have been reported as plant pathogens, endophytes, and saprophytes on a wide range of host plants worldwide. Their precise identification is problematic since many Diaporthe species can colonize a single host plant, whereas the same Diaporthe species can inhabit many hosts. Recently, Diaporthe has been proven to be a rich source of bioactive secondary metabolites. In our initial study, 40 Diaporthe isolates were analyzed for their metabolite production. A total of 153 compounds were identified based on their spectroscopic properties-Ultraviolet-visible and mass spectrometry. From these, 43 fungal metabolites were recognized as potential chemotaxonomic markers, mostly belonging to the drimane sesquiterpenoid-phthalide hybrid class. This group included mainly phytotoxic compounds such as cyclopaldic acid, altiloxin A, B, and their derivatives. To the best of our knowledge, this is the first report on the metabolomic studies on Diaporthe eres species complex from fruit trees in the South-Eastern Poland. The results from our study may provide the basis for the future research on the isolation of identified metabolites and on their bioactive potential for agricultural applications as biopesticides or biofertilizers.

The Synthesis of 3-(R)- and 3-(S)-Hydroxyeicosapentaenoic Acid

Monohydroxylated polyunsaturated fatty acids belonging to the oxylipin class of natural products are present in marine and terrestrial sources as well as in the human body. Due to their biological activities and role in diverse biosynthetic pathways, oxylipins biosynthesized from eicosapentaenoic acid and arachidonic acid have attracted great interest from the scientific community. One example is 3-hydroxyeicosapentaenoic acid where the absolute configuration at C-3 has only been tentatively assigned. In this paper, studies on acetate type aldol reactions that enabled the preparation of 3-(R)-hydroxyeicosapentaenoic acid (3R-HETE, 2) and its enantiomer are presented.

The Influence of Artificial Fusarium Infection on Oat Grain Quality

Adverse environmental conditions, such as various biotic and abiotic stresses, are the primary reason for decreased crop productivity. Oat, as one of the world's major crops, is an important cereal in human nutrition. The aim of this work was to analyze the effect of inoculation with two species of the genus Fusarium on the selected qualitative parameters of oat grain intended for the food industry. Artificial inoculation caused a statistically significant decrease in the content of starch, oleic, linoleic, and α-linolenic acids in oat grains compared to the control. Moreover, artificial inoculation had no statistically significant effect on the content of β-D-glucans, total dietary fiber, total lipids, palmitic, stearic, and cis-vaccenic acids. An increase in the content of polyunsaturated fatty acids in oat grains was observed after inoculation. The most important indicator of Fusarium infection was the presence of the mycotoxin deoxynivalenol in the grain. The content of β-D-glucans, as a possible protective barrier in the cell wall, did not have a statistically significant effect on the inoculation manifestation in the grain.

Gastric Perforation Associated with Candidiasis and NSAIDS

Invasive candidiasis is an important health-care-associated fungal infection. Candida is often described as an opportunistic pathogen. It is commensal flora in the gastrointestinal tract. Invasive candidiasis can happen usually because of a consequence of increased or abnormal colonization together with a local or generalized defect in host defenses. Candidiasis can occur in patients with HIV, therapy with a broad-spectrum antibiotic, transplant organ, and immunocompromised. Most cases of gastric perforation occur as complications of Peptic Ulcer Disease (PUD), Nonsteroidal Anti-Inflammatory Drugs (NSAIDs) and gastric neoplasms, but candidiasis as a cause of gastric perforation is very rare. This study aims to reveal the correlation between gastric perforation with candidiasis and NSAIDs. It was reported that a 57-year-old East Java Indonesian female presented with severe epigastric pain, generalized peritonitis, fever, nausea also vomiting and had a history of NSAIDs used for five years. The patient was taken to the general surgery of Dr. Sutomo Surabaya Hospital and performed exploratory laparotomy. A gastric perforation was discovered in the antrum. Microbiology culture examination from biopsy gastric tissue revealed an intense fungal growth from sabouraudagar medium and there is no other microorganism that grew in aerobic culture. Candida albicans was identified by VITEK® 2 COMPACT. Histopathological examination from biopsy gastric tissue was performed by Olympus CX-21 microscope, showed invasive Candida albicans consisting of numerous fungal yeasts and pseudohyphae invading and destroying the gastric wall. The patient was subsequently treated with fluconazole anti-fungal and discharge home after nine days postoperative period in good condition. From this result, we suggest using an antifungal treatment for patients who use NSAIDs for long periods to prevent candidiasis.

Fumonisin B1: A Tool for Exploring the Multiple Functions of Sphingolipids in Plants

Fumonisin toxins are produced by Fusarium fungal pathogens. Fumonisins are structural analogs of sphingosine and potent inhibitors of ceramide synthases (CerSs); they disrupt sphingolipid metabolism and cause disease in plants and animals. Over the past three decades, researchers have used fumonisin B1 (FB1), the most common fumonisin, as a probe to investigate sphingolipid metabolism in yeast and animals. Although the physiological effects of FB1 in plants have yet to be investigated in detail, forward and reverse genetic approaches have revealed many genes involved in these processes. In this review, we discuss the intricate network of signaling pathways affected by FB1, including changes in sphingolipid metabolism and the effects of these changes, with a focus on our current understanding of the multiple effects of FB1 on plant cell death and plant growth. We analyze the major findings that highlight the connections between sphingolipid metabolism and FB1-induced signaling, and we point out where additional research is needed to fill the gaps in our understanding of FB1-induced signaling pathways in plants.

Sporulation in Ashbya gossypii

Ashbya gossypii is a filamentous ascomycete belonging to the yeast family of Saccharomycetaceae. At the end of its growth phase Ashbya generates abundant amounts of riboflavin and spores that form within sporangia derived from fragmented cellular compartments of hyphae. The length of spores differs within species of the genus. Needle-shaped Ashbya spores aggregate via terminal filaments. A. gossypii is a homothallic fungus which may possess a and α mating types. However, the solo-MATa type strain is self-fertile and sporulates abundantly apparently without the need of prior mating. The central components required for the regulation of sporulation, encoded by IME1, IME2, IME4, KAR4, are conserved with Saccharomyces cerevisiae. Nutrient depletion generates a strong positive signal for sporulation via the cAMP-PKA pathway and SOK2, which is also essential for sporulation. Strong inhibitors of sporulation besides mutations in the central regulatory genes are the addition of exogenous cAMP or the overexpression of the mating type gene MATα2. Sporulation has been dissected using gene-function analyses and global RNA-seq transcriptomics. This revealed a role of Msn2/4, another potential PKA-target, for spore wall formation and a key dual role of the protein A kinase Tpk2 at the onset of sporulation as well as for breaking the dormancy of spores to initiate germination. Recent work has provided an overview of ascus development, regulation of sporulation and spore maturation. This will be summarized in the current review with a focus on the central regulatory genes. Current research and open questions will also be discussed.

Disturbance in biosynthesis of arachidonic acid impairs the sexual development of the onion blight pathogen Stemphylium eturmiunum

The formation of sexual fruiting bodies for plant pathogenic fungi is a key strategy to propagate their progenies upon environmental stresses. Stemphylium eturmiunum is an opportunistic plant pathogen fungus causing blight in onion. This self-fertilizing filamentous ascomycete persists in the soil by forming pseudothecia, the sexual fruiting body which helps the fungus survive in harsh environments. However, the regulatory mechanism of pseudothecial formation remains unknown. To uncover the mechanism for pseudothecial formation so as to find a practical measure to control the propagation of this onion pathogen, we tentatively used DNA methyltransferase inhibitor 5-azacytidine (5-AC) to treat S. eturmiunum. 5-AC treatment silenced the gene-encoding monoacylglycerol lipase (magl) concomitant with the presence of the inheritable fluffy phenotype and defectiveness in pseudothecial development. Moreover, the silence of magl also resulted in a reduction of arachidonic acid (AA) formation from 27 ± 3.1 µg/g to 9.5 ± 1.5 µg/g. To correlate the biosynthesis of AA and pseudothecial formation, we created magl knockdown and overexpression strains. Knockdown of magl reduced AA to 11 ± 2.4 µg/g, which subsequently disabled pseudothecial formation. In parallel, overexpression of magl increased AA to 37 ± 3.4 µg/g, which also impaired pseudothecial formation. Furthermore, exogenous addition of AA to the culture of magl-silenced or magl knockdown strains rescued the pseudothecial formation but failed in the gpr1 knockdown strain of S. eturmiunum, which implicates the involvement of AA in signal transduction via a putative G protein-coupled receptor 1. Thus, AA at a cellular level of 27 ± 3.1 µg/g is essential for sexual development of S. eturmiunum. Disturbance in the biosynthesis of AA by up- and down-regulating the expression of magl disables the pseudothecial development. The specific requirement for AA in pseudothecial development by S. eturmiunum provides a hint to curb this onion pathogen: to impede pseudothecial formation by application of AA.

Molecular Basis of Resistance to Fusarium Ear Rot in Maize

The impact of climate change has been identified as an emerging issue for food security and safety, and the increased incidence of mycotoxin contamination in maize over the last two decades is considered a potential emerging hazard. Disease control by chemical and agronomic approaches is often ineffective and increases the cost of production; for this reason the exploitation of genetic resistance is the most sustainable method for reducing contamination. The review focuses on the significant advances that have been made in the development of transcriptomic, genetic and genomic information for maize, Fusarium verticillioides molds, and their interactions, over recent years. Findings from transcriptomic studies have been used to outline a specific model for the intracellular signaling cascade occurring in maize cells against F. verticillioides infection. Several recognition receptors, such as receptor-like kinases and R genes, are involved in pathogen perception, and trigger down-stream signaling networks mediated by mitogen-associated protein kinases. These signals could be orchestrated primarily by hormones, including salicylic acid, auxin, abscisic acid, ethylene, and jasmonic acid, in association with calcium signaling, targeting multiple transcription factors that in turn promote the down-stream activation of defensive response genes, such as those related to detoxification processes, phenylpropanoid, and oxylipin metabolic pathways. At the genetic and genomic levels, several quantitative trait loci (QTL) and single-nucleotide polymorphism markers for resistance to Fusarium ear rot deriving from QTL mapping and genome-wide association studies are described, indicating the complexity of this polygenic trait. All these findings will contribute to identifying candidate genes for resistance and to applying genomic technologies for selecting resistant maize genotypes and speeding up a strategy of breeding to contrast disease, through plants resistant to mycotoxin-producing pathogens.

Elucidation of the Role of 3-Hydroxy Fatty Acids in Cryptococcus-amoeba Interactions

We previously reported that 3-hydroxy fatty acids promoted the survival of cryptococcal cells when acted upon by amoebae. To expand on this, the current study sought to explain how these molecules may protect cells. Our data suggest that 3-hydroxy fatty acids may subvert the internalization of cryptococcal cells via suppression of the levels of a fetuin A-like amoebal protein, which may be important for enhancing phagocytosis. Additionally, we show that an acapsular strain (that is devoid of 3-hydroxy fatty acids) was protected against the effects of hydrogen peroxide when exogenous 3-hydroxy fatty acids were present, but not in the absence of 3-hydroxy fatty acids. A similar response profile was noted when a strain with a capsule was challenged with hydrogen peroxide. We also show that cryptococcal cells that naturally produce 3-hydroxy fatty acids were more resistant to the effects of amoebapore (an amoeba-specific hydrolytic enzyme), compared to cells that do not produce these molecules. Taken together, our findings suggest that 3-hydroxy fatty acids possess an anti-phagocytic activity that may be expressed when cells interact with macrophages. This may allow the yeast cells to evade immuno-processing.

Production of cross-kingdom oxylipins by pathogenic fungi: An update on their role in development and pathogenicity

Oxylipins are a class of molecules derived from the incorporation of oxygen into polyunsaturated fatty acid substrates through the action of oxygenases. While extensively investigated in the context of mammalian immune responses, over the last decade it has become apparent that oxylipins are a common means of communication among and between plants, animals, and fungi to control development and alter host-microbe interactions. In fungi, some oxylipins are derived nonenzymatically while others are produced by lipoxygenases, cyclooxygenases, and monooxygenases with homology to plant and human enzymes. Recent investigations of numerous plant and human fungal pathogens have revealed oxylipins to be involved in the establishment and progression of disease. This review highlights oxylipin production by pathogenic fungi and their role in fungal development and pathogen/host interactions.

Microbial synthesis of plant oxylipins from γ-linolenic acid through designed biotransformation pathways

Secondary metabolites of plants are often difficult to synthesize in high yields because of the large complexity of the biosynthetic pathways and challenges encountered in the functional expression of the required biosynthetic enzymes in microbial cells. In this study, the biosynthesis of plant oxylipins--a family of oxygenated unsaturated carboxylic acids--was explored to enable a high-yield production through a designed microbial synthetic system harboring a set of microbial enzymes (i.e., fatty acid double-bond hydratases, alcohol dehydrogenases, Baeyer-Villiger monooxygenases, and esterases) to produce a variety of unsaturated carboxylic acids from γ-linolenic acid. The whole cell system of the recombinant Escherichia coli efficiently produced (6Z,9Z)-12-hydroxydodeca-6,9-dienoic acid (7), (Z)-9-hydroxynon-6-enoic acid (15), (Z)-dec-4-enedioic acid (17), and (6Z,9Z)-13-hydroxyoctadeca-6,9-dienoic acid (2). This study demonstrated that various secondary metabolites of plants can be produced by implementing artificial biosynthetic pathways into whole-cell biocatalysis.

Production of hydroxy fatty acids by microbial fatty acid-hydroxylation enzymes

Hydroxy fatty acids are widely used in chemical, food, and cosmetic industries as starting materials for the synthesis of polymers and as additives for the manufacture of lubricants, emulsifiers, and stabilizers. They have antibiotic, anti-inflammatory, and anticancer activities and therefore can be applied for medicinal uses. Microbial fatty acid-hydroxylation enzymes, including P450, lipoxygenase, hydratase, 12-hydroxylase, and diol synthase, synthesize regio-specific hydroxy fatty acids. In this article, microbial fatty acid-hydroxylation enzymes, with a focus on region-specificity and diversity, are summarized and the production of mono-, di-, and tri-hydroxy fatty acids is introduced. Finally, the production methods of regio-specific and diverse hydroxy fatty acids, such as gene screening, protein engineering, metabolic engineering, and combinatory biosynthesis, are suggested.

The "firing cannons" of Dipodascopsis uninucleata var. uninucleata

According to literature, the elongated ascospores of Dipodascopsis uninucleata var. uninucleata exhibit smart movement when forcefully ejected from bottle-shaped asci. This type of movement is defined as the unique patterns of non-random movement of ascospores with specialized morphology thereby facilitating release from asci. Smart movement is required to actively release ascospores individually through the narrow ascus neck, without causing an obstruction and blocking ascospore release. However, little is known about the propulsion mechanism of this cannon-type release system. We show that asci of this yeast contain a central channel (barrel) filled with ascospores. These are surrounded by a sheath-like structure that lines the inner surface of the ascus wall. We found that this sheath is responsible for forcing the naked ascospores out of the ascus by exerting turgor pressure from the bottom towards the tip of the ascus. This cannon firing system is in contrast to that found in Dipodascus geniculatus, where no sheaths lining the ascus interior were observed. Instead, sheaths were found enveloping each ascospore.

The interplay between NSAIDs and Candida albicans on the gastrointestinal tract of guinea pigs

Recent studies suggest that Candida albicans colonization is associated with several gastrointestinal inflammatory disorders and is also responsible for the delay in ulcer healing. No data are reported about the effects of C. albicans on the nonsteroidal anti-inflammatory drugs (NSAIDs)-induced necroinflammatory lesions. On the other hand, beneficial effects of NSAIDs regarding the colonization potential with C. albicans have been reported. Our aim was to investigate whether the association between NSAIDs and C. albicans could potentially induce necroinflammatory lesions in the guinea pigs gastric and enteral mucosa. Three interventional groups of 11 guinea pigs each were investigated after 5 days of receiving indomethacin, C. albicans or the association of both. C. albicans and necroinflammatory lesions were graded based on histological examinations. Statistical analysis used Mann-Whitney nonparametric test. NSAIDs did not significantly decrease C. albicans colonization grades on gastrointestinal mucosa. Administration of indomethacin subsequent to C. albicans determined significantly more severe necroinflammatory lesions compared to group that only received C. albicans. The association of NSAIDs and C. albicans did not cause significantly more severe degenerative or inflammatory lesions compared to the administration of only NSAIDs in this experimental model. Associations between NSAIDs and C. albicans caused significantly more severe necroinflammatory injuries than the lesions produced by C. albicans, without enhancing the mucosal injury or inflammation caused by NSAIDs.

Arachidonic acid metabolites in pathogenic yeasts

Although most of what is known about the biology and function of arachidonic acid metabolites comes from the study of mammalian biology, these compounds can also be produced by lower eukaryotes, including yeasts and other fungi. It is also in this group of organisms that the least is known about the metabolic pathways leading to the production of these compounds as well as the functions of these compounds in the biology of fungi and yeasts. This review will deal with the discovery of oxylipins from polyunsaturated fatty acids, and more specifically the arachidonic acid derived eicosanoids, such as 3-hydroxy eicosatetraenoic acid, prostaglandin F_2α and prostaglandin E₂, in yeasts starting in the early 1990s. This review will also focus on what is known about the metabolic pathways and/or proteins involved in the production of these compounds in pathogenic yeasts. The possible roles of these compounds in the biology, including the pathology, of these organisms will be discussed.

The presence of 3-hydroxy oxylipins in pathogenic microbes

There is a sufficient body of work documenting the distribution of 3-hydroxy oxylipins in microbes. However, there is limited information on the role of these compounds in microbial pathogenesis. When derived from mammalian cells, these compounds regulate patho-biological processes, thus an understanding of 3-hydroxy oxylipin function and metabolism could prove important in shedding light on how these compounds mediate cellular pathology and physiology. This could present 3-hydroxy oxylipin biosynthetic pathways as targets for drug development. In this minireview, we interrogate the relevant yeast and bacterial 3-hydroxy oxylipin literature in order to appreciate how these compounds may influence the inflammatory response leading to disease development.

The anti-mitochondrial antifungal assay for the discovery and development of new drugs

INTRODUCTION

New targets and drugs are constantly searched for to effectively combat fungal infections and diseases such as cancer. Mitochondria, as the main powerhouses of eukaryotic cells, must be regarded as important targets for the development of new therapies. This has lead to the development of a fungal assay that shows potential in the selection of new antifungal and anticancer drugs as well as the identification of compounds that are toxic to human mitochondria.

AREAS COVERED

In this review the authors discuss the development of a potential method of drug discovery that targets mitochondrial function. The authors cover the application of new nanotechnology as well as fungal systematic research where the link between fungal fruiting structures, cell growth, increased mitochondrial activity and susceptibility to a variety of anti-mitochondrial drugs is assessed.

EXPERT OPINION

This assay shows potential to select anti-mitochondrial drugs as a first screen. This should be followed up by more specific in vitro and in vivo tests to pinpoint the type of anti-mitochondrial activity exerted by these drugs, if any. This is because the possibility exists that compounds regarded as anti-mitochondrial may not inhibit mitochondrial function but other fruiting structure developmental stages and therefore yield false positives. To enhance our knowledge on how these drugs act at the structural level, the authors recommend Nano Scanning Auger Microscopy as the tool of choice.

Oxylipins in fungi

In nearly every living organism, metabolites derived from lipid peroxidation, the so-called oxylipins, are involved in regulating developmental processes as well as environmental responses. Among these bioactive lipids, the mammalian and plant oxylipins are the best characterized, and much information about their physiological role and biosynthetic pathways has accumulated during recent years. Although the occurrence of oxylipins and enzymes involved in their biosynthesis has been studied for nearly three decades, knowledge about fungal oxylipins is still scarce as compared with the situation in plants and mammals. However, the research performed so far has shown that the structural diversity of oxylipins produced by fungi is high and, furthermore, that the enzymes involved in oxylipin metabolism are diverse and often exhibit unusual catalytic activities. The aim of this review is to present a synopsis of the oxylipins identified so far in fungi and the enzymes involved in their biosynthesis.

Morphological transitions governed by density dependence and lipoxygenase activity in Aspergillus flavus

Aspergillus flavus differentiates to produce asexual dispersing spores (conidia) or overwintering survival structures called sclerotia. Results described here show that these two processes are oppositely regulated by density-dependent mechanisms and that increasing the cell density (from 10(1) to 10(7) cells/plate) results in the lowest numbers of sclerotial and the highest numbers of conidial. Extract from spent medium of low-cell-density cultures induced a high-sclerotium-number phenotype, whereas high-cell-density extract increased conidiation. Density-dependent development is also modified by changes in lipid availability. Exogenous linoleic acid increased sclerotial production at intermediate cell densities (10(4) and 10(5) cells/plate), whereas oleic and linolenic acids inhibited sclerotium formation. Deletion of Aflox encoding a lipoxygenase (LOX) greatly diminished density-dependent development of both sclerotia and conidia, resulting in an overall increase in the number of sclerotia and a decrease in the number of conidia at high cell densities (>10(5) cells/plate). Aflox mutants showed decreased linoleic acid LOX activity. Taken together, these results suggest that there is a quorum-sensing mechanism in which a factor(s) produced in dense cultures, perhaps a LOX-derived metabolite, activates conidium formation, while a factor(s) produced in low-density cultures stimulates sclerotium formation.

Variation in yeast mitochondrial activity associated with asci

An increase in mitochondrial membrane potential (ΔΨm) and mitochondrially produced 3-hydroxy (3-OH) oxylipins was experienced in asci of the nonfermentative yeasts Galactomyces reessii and Lipomyces starkeyi and the fermentative yeasts Pichia farinosa and Schizosaccharomyces octosporus . Strikingly, asci of Zygosaccharomyces bailii showed no increase in mitochondrial activity (ΔΨm and oxylipin production). As expected, oxygen deprivation only inhibited ascus formation in those yeasts with increased ascus mitochondrial activity. We conclude that ascus formation in yeasts is not always dependent on mitochondrial activity. In this case, fermentation may provide enough energy for ascus formation in Z. bailii.

Oxylipin and mitochondrion probes to track yeast sexual cells

When oxylipin and mitochondrion probes, i.e., fluorescing antibodies specific for 3-hydroxy fatty acids (3-OH oxylipins) and rhodamine 123 (Rh123), were added to yeast cells, these probes accumulated mainly in the sexual cells (i.e., both associated with ascospores) and not in the vegetative cells. This suggests increased mitochondrial activity in asci, since 3-OH oxylipins are mitochondrially produced and it is known that Rh123 accumulates selectively in functional mitochondria that maintain a high transmembrane potential (ΔΨm). This increased activity may be necessary for the production and effective release of the many spores found in single-celled asci. These results may be useful in the rapid identification of asci and in yeast sexual spore mechanics, which may find application in yeast systematics as well as hydro-, aero-, and nano-technologies.

The influence of acetylsalicylic acid on oxylipin migration in Cryptococcus neoformans var. neoformans UOFS Y-1378

In this paper we report the influence of acetylsalicylic acid on oxylipin migration in Cryptococcus neoformans var. neoformans UOFS Y-1378, previously isolated from human bone lesion. Transmission electron microscopy suggests that osmiophilic material originates in mitochondria and is deposited inside the yeast cell wall, from which it is excreted into the environment, along capsule protuberances, or through capsule detachments. Previous studies using immunogold labeling indicate that these osmiophilic layers contain 3-hydroxy oxylipins. In this study, the addition of acetylsalicylic acid (an inhibitor of mitochondrial function) in increasing amounts to the cells abrogated the migration of osmiophilic material, as well as capsule detachment from cell walls, and hence, oxylipin excretion. Consequently, we hypothesize that 3-hydroxy oxylipins are produced in mitochondria, probably via incomplete beta-oxidation or fatty acid synthesis, from which they are deposited inside the cell wall and excreted through tubular protuberances attached to the surrounding capsules and (or) through detachment of these oxylipin-containing capsules.

Distribution of 3-hydroxy oxylipins and acetylsalicylic acid sensitivity in Cryptococcus species

Using a well tested antibody specific for 3-hydroxy oxylipins, we mapped the presence of these oxylipins in selected Cryptococcus ( Filobasidiella ) species. Immunofluorescence microscopy studies revealed that these compounds are deposited on cell wall surfaces, appendages, and collarettes. In vitro studies revealed that growth of Cryptococcus species was inhibited by acetylsalicylic acid (which is known to inhibit mitochondrial function, including the production of 3-hydroxy oxylipins) at concentrations as low as 1 mmol/L. The results suggest that acetylsalicylic acid is effective in controlling the growth of tested pathogens, probably by targeting their mitochondria. This study further expands the known function of this anti-inflammatory drug as anti-fungal agent.

3-hydroxy fatty acids found in capsules of Cryptococcus neoformans

Using immunofluorescence confocal laser scanning microscopy, immunogold transmission electron microscopy and gas chromatography--mass spectrometry, we demonstrated the presence of 3-hydroxy fatty acids in Cryptococcus neoformans. Our results suggest that these oxylipins accumulate in capsules where they are released as hydrophobic droplets through tubular protuberances into the surrounding medium.

Role of oxylipins and other lipid mediators in fungal pathogenesis

Recently there has been a focused interest in the production of bioactive lipid metabolites from eukaryotic microbes, and in the roles that these molecules play in development and pathological processes. These metabolites have long been known in mammals to be potent modulators of various physiological processes, such as the regulation of inflammation. This area of research has been of particular interest in fungi, where oxylipin production has been correlated with pathogenicity. The aim of this review is to discuss recent findings that show how oxylipins and other lipid mediators affect fungal development, quorum sensing and effecter molecule production, which all amount to a global control by oxylipins of fungal pathogenesis.

Disruption of a maize 9-lipoxygenase results in increased resistance to fungal pathogens and reduced levels of contamination with mycotoxin fumonisin

Plant oxylipins, produced via the lipoxygenase (LOX) pathway, function as signals in defense and development. In fungi, oxylipins are potent regulators of mycotoxin biosynthesis and sporogenesis. Previous studies showed that plant 9-LOX-derived fatty acid hydroperoxides induce conidiation and mycotoxin production. Here, we tested the hypothesis that oxylipins produced by the maize 9-LOX pathway are required by pathogens to produce spores and mycotoxins and to successfully colonize the host. Maize mutants were generated in which the function of a 9-LOX gene, ZmLOX3, was abolished by an insertion of a Mutator transposon in its coding sequence, which resulted in reduced levels of several 9-LOX-derived hydroperoxides. Supporting our hypothesis, conidiation and production of the mycotoxin fumonisin B1 by Fusarium verticillioides were drastically reduced in kernels of the lox3 mutants compared with near-isogenic wild types. Similarly, conidia production and disease severity of anthracnose leaf blight caused by Colletotrichum graminicola were significantly reduced in the lox3 mutants. Moreover, lox3 mutants displayed increased resistance to southern leaf blight caused by Cochliobolus heterostrophus and stalk rots caused by both F. verticillioides and C. graminicola. These data strongly suggest that oxylipin metabolism mediated by a specific plant 9-LOX isoform is required for fungal pathogenesis, including disease development and production of spores and mycotoxins.

Oxylipins as developmental and host-fungal communication signals

Pathogenic microbes and their hosts have acquired complex signalling mechanisms to appraise themselves of the environmental milieu in the ongoing battle for survival. Several recent studies have implicated oxylipins as a novel class of host-microbe signalling molecules. Oxylipins represent a vast and diverse family of secondary metabolites that originate from the oxidation or further conversion of polyunsaturated fatty acids. Among the microbial oxylipins, the fungal oxylipins are best characterized and function as hormone-like signals that modulate the timing and balance between asexual and sexual spore development in addition to toxin production. Coupled with other studies that implicate a role for fungal oxylipins in pathogenesis by Aspergillus and Candida spp., these results suggest that host and microbial oxylipins might interfere with the metabolism, perception or signalling processes of each other.

The multifunctional beta-oxidation enzyme is required for full symptom development by the biotrophic maize pathogen Ustilago maydis

The transition from yeast-like to filamentous growth in the biotrophic fungal phytopathogen Ustilago maydis is a crucial event for pathogenesis. Previously, we showed that fatty acids induce filamentation in U. maydis and that the resulting hyphal cells resemble the infectious filaments observed in planta. To explore the potential metabolic role of lipids in the morphological transition and in pathogenic development in host tissue, we deleted the mfe2 gene encoding the multifunctional enzyme that catalyzes the second and third reactions in beta-oxidation of fatty acids in peroxisomes. The growth of the strains defective in mfe2 was attenuated on long-chain fatty acids and abolished on very-long-chain fatty acids. The mfe2 gene was not generally required for the production of filaments during mating in vitro, but loss of the gene blocked extensive proliferation of fungal filaments in planta. Consistent with this observation, mfe2 mutants exhibited significantly reduced virulence in that only 27% of infected seedlings produced tumors compared to 88% tumor production upon infection by wild-type strains. Similarly, a defect in virulence was observed in developing ears upon infection of mature maize plants. Specifically, the absence of the mfe2 gene delayed the development of teliospores within mature tumor tissue. Overall, these results indicate that the ability to utilize host lipids contributes to the pathogenic development of U. maydis.

Acetylsalicylic acid as antifungal in Eremothecium and other yeasts

Interesting distribution patterns of acetylsalicylic acid (ASA, aspirin) sensitive 3-hydroxy (OH) oxylipins were previously reported in some representatives of the yeast genus Eremothecium--an important group of plant pathogens. Using immunofluorescence microscopy and 3-OH oxylipin specific antibodies in this study, we were able to map the presence of these compounds also in other Eremothecium species. In Eremothecium cymbalariae, these oxylipins were found to cover mostly the spiky tips of narrowly triangular ascospores while in Eremothecium gossypii, oxylipins covered the whole spindle-shaped ascospore with terminal appendages. The presence of these oxylipins was confirmed by chemical analysis. When ASA, a 3-OH oxylipin inhibitor, was added to these yeasts in increasing concentrations, the sexual stage was found to be the most sensitive. Our results suggest that 3-OH oxylipins, produced by mitochondria through incomplete beta-oxidation, are associated with the development of the sexual stages in both yeasts. Strikingly, preliminary studies on yeast growth suggest that yeasts, characterized by mainly an aerobic respiration rather than a fermentative pathway, are more sensitive to ASA than yeasts characterized by both pathways. These data further support the role of mitochondria in sexual as well as asexual reproduction of yeasts and its role to serve as a target for ASA antifungal action.

Oxylipin-coated hat-shaped ascospores of Ascoidea corymbosa

We previously implicated 3-hydroxy oxylipins and ascospore structure in ascospore release from enclosed asci. Using confocal laser scanning microscopy on cells stained with fluorescein-coupled, 3-hydroxy oxylipin-specific antibodies, we found that oxylipins are specifically associated with ascospores and not the vegetative cells or ascus wall of Ascoidea corymbosa. Using gas chromatography – mass spectrometry the oxylipin 3-hydroxy 17:0 could be identified. Here, we visualize for the first time the forced release of oxylipin-coated, hat-shaped ascospores from terminally torn asci, probably through turgor pressure. We suggest that oxylipin-coated, razor-sharp, hat-shaped ascospore brims may play a role in rupturing the ascus to affect release.Key words: Ascoidea corymbosa, ascospore release, confocal laser scanning microscopy, gas chromatography – mass spectrometry, hat-shaped ascospores, 3-hydroxy oxylipins.

Mapping the distribution of 3-hydroxy oxylipins in the ascomycetous yeast Saturnispora saitoi

The distribution of 3-hydroxy oxylipins in Saturnispora saitoi was mapped using immunofluorescence microscopy. Fluorescence was observed on aggregating ascospores, indicating the presence of 3-hydroxy oxylipins on the surface or between ascospores. The oxylipin was identified as 3-hydroxy 9:1 using gas chromatography mass spectrometry. Furthermore, ultrastructural studies using scanning and transmission electron microscopy on ascospores revealed a clear equatorial ledge surrounding oval-shaped ascospores.

Signalling pathways connecting mycotoxin production and sporulation

SUMMARY Mycotoxin contamination of food and feed presents a serious food safety issue on a global scale, causing tremendous yield and economic losses. These toxins, produced largely by members of the genera Aspergillus and Fusarium, represent a subset of the impressive array of secondary metabolites produced by filamentous fungi. Some secondary metabolites are associated temporally and functionally with sporulation. In Aspergillus and Fusarium, sporulation and mycotoxin production are both regulated by G protein signalling pathways. G protein signalling pathways commonly regulate fungal development, stress response and expression of virulence traits. In addition, fungal development is influenced by external factors. Among these are lipids, and in particular, oxylipin signals, which may be derived from either the fungus or infected seeds. Regardless of origin, oxylipins have the potential to elicit profound changes in both sporulation and mycotoxin production in the fungus. Signal transduction via G protein signalling pathways represents one mechanism by which oxylipin signals might elicit these changes. Therefore, in this review we integrate discussion of oxylipin signals and of G protein signalling cascades as regulators of fungal development.

Oxylipins act as determinants of natural product biosynthesis and seed colonization in Aspergillus nidulans

Secreted, hormone-like lipogenic molecules, called oxylipins, mediate the balance of asexual to sexual spore ratio in Aspergillus nidulans. Oxylipin production in this fungus is dependent on developmental regulation of three conserved fatty acid oxygenases, PpoA, PpoB and PpoC. Here, we show that in addition to altering spore ratios, loss of ppo genes affect natural product biosynthesis and seed colonization. DeltappoA;DeltappoC and DeltappoA;DeltappoB;DeltappoC mutants were unable to produce the mycotoxin sterigmatocystin (ST) in vitro or in planta but in contrast overproduced the antibiotic penicillin (PN). These findings were correlated with decreased expression of genes involved in ST biosynthesis and increased expression of a PN biosynthetic gene, thus suggesting that oxylipin species regulate secondary metabolites at the transcriptional level. Additionally, the DeltappoA;DeltappoC and the DeltappoA;DeltappoB;DeltappoC mutants were defective in colonization of peanut seeds as reflected by a decrease in conidiation and production of the seed degradative enzyme lipase. These results indicate that oxylipin production is important for host colonization and mycotoxin production and may provide a promising target for future control strategies.

Oxygenation by COX-2 (cyclo-oxygenase-2) of 3-HETE (3-hydroxyeicosatetraenoic acid), a fungal mimetic of arachidonic acid, produces a cascade of novel bioactive 3-hydroxyeicosanoids

Cyclo-oxygenases-1/2 (COX-1/2) catalyse the oxygenation of AA (arachidonic acid) and related polyunsaturated fatty acids to endoperoxide precursors of prostanoids. COX-1 is referred to as a constitutive enzyme involved in haemostasis, whereas COX-2 is an inducible enzyme expressed in inflammatory diseases and cancer. The fungus Dipodascopsis uninucleata has been shown by us to convert exogenous AA into 3(R)-HETE [3(R)-hydroxy-5Z,8Z,11Z,14Z-eicosatetraenoic acid]. 3R-HETE is stereochemically identical with AA, except that a hydroxy group is attached at its C-3 position. Molecular modelling studies with 3-HETE and COX-1/2 revealed a similar enzyme-substrate structure as reported for AA and COX-1/2. Here, we report that 3-HETE is an appropriate substrate for COX-1 and -2, albeit with a lower activity of oxygenation than AA. Oxygenation of 3-HETE by COX-2 produced a novel cascade of 3-hydroxyeicosanoids, as identified with EI (electron impact)-GC-MS, LC-MS-ES (electrospray) and LC-MS-API (atmospheric pressure ionization) methods. Evidence for in vitro production of 3-hydroxy-PGE2 (3-hydroxy-prostaglandin E2) was obtained upon infection of HeLa cells with Candida albicans at an MOI (multiplicity of infection) of 100. Analogous to interaction of AA and aspirin-treated COX-2, 3-HETE was transformed by acetylated COX-2 to 3,15-di-HETE (3,15-dihydroxy-HETE), whereby C-15 showed the (R)-stereochemistry. 3-Hydroxy-PGs are potent biologically active compounds. Thus 3-hydroxy-PGE2 induced interleukin-6 gene expression via the EP3 receptor (PGE2 receptor 3) in A549 cells, and raised cAMP levels via the EP4 receptor in Jurkat cells. Moreover, 3R,15S-di-HETE triggered the opening of the K+ channel in HTM (human trabecular meshwork) cells, as measured by the patch-clamp technique. Since many fatty acid disorders are associated with an 'escape' of 3-hydroxy fatty acids from the b-oxidation cycle, the production of 3-hydroxyeicosanoids may be critical in modulation of effects of endogenously produced eicosanoids.

Oxylipin covered ascospores of Eremothecium coryli

Eremothecium coryli is known to produce intriguing spindle-shaped ascospores with long and thin whip-like appendages. Here, ultra structural studies using scanning electron microscopy, indicate that these appendages serve to coil around themselves and around ascospores causing spore aggregation. Furthermore, using immunofluorescence confocal laser scanning microscopy it was found that hydrophobic 3-hydroxy oxylipins cover the surfaces of these ascospores. Using gas chromatography-mass spectrometry, only the oxylipin 3-hydroxy 9:1 (a monounsaturated fatty acid containing a hydroxyl group on carbon 3) could be identified. Sequential digital imaging suggests that oxylipin-coated spindle-shaped ascospores are released from enclosed asci probably by protruding through an already disintegrating ascus wall.

Evaluation of the antimicrobial activities of plant oxylipins supports their involvement in defense against pathogens

Plant oxylipins are a large family of metabolites derived from polyunsaturated fatty acids. The characterization of mutants or transgenic plants affected in the biosynthesis or perception of oxylipins has recently emphasized the role of the so-called oxylipin pathway in plant defense against pests and pathogens. In this context, presumed functions of oxylipins include direct antimicrobial effect, stimulation of plant defense gene expression, and regulation of plant cell death. However, the precise contribution of individual oxylipins to plant defense remains essentially unknown. To get a better insight into the biological activities of oxylipins, in vitro growth inhibition assays were used to investigate the direct antimicrobial activities of 43 natural oxylipins against a set of 13 plant pathogenic microorganisms including bacteria, oomycetes, and fungi. This study showed unequivocally that most oxylipins are able to impair growth of some plant microbial pathogens, with only two out of 43 oxylipins being completely inactive against all the tested organisms, and 26 oxylipins showing inhibitory activity toward at least three different microbes. Six oxylipins strongly inhibited mycelial growth and spore germination of eukaryotic microbes, including compounds that had not previously been ascribed an antimicrobial activity, such as 13-keto-9(Z),11(E),15(Z)-octadecatrienoic acid and 12-oxo-10,15(Z)-phytodienoic acid. Interestingly, this first large-scale comparative assessment of the antimicrobial effects of oxylipins reveals that regulators of plant defense responses are also the most active oxylipins against eukaryotic microorganisms, suggesting that such oxylipins might contribute to plant defense through their effects both on the plant and on pathogens, possibly through related mechanisms.

Ascospore release from bottle-shaped asci in

Yeasts utilize different mechanisms to release ascospores of different lengths from bottle-shaped asci. Using electron microscopy, confocal laser scanning microscopy, gas chromatography-mass spectrometry and digital live imaging, the individual release of oval ascospores from tight-fitting narrow bottle-necks, is reported in the yeast Dipodascus albidus. These ascospores are surrounded by compressible, oxylipin-coated sheaths enabling ascospores to slide past each other when forced by turgor pressure and by possible sheath contractions towards the narrowing ascus-neck. In this paper, the release mechanisms of ascospores of various lengths from bottle-shaped asci and produced by different yeasts are compared. We suggest that different release mechanisms, utilizing compressible sheaths or geared-alignment, have possibly evolved to compensate for variation in ascospore length. Alternatively, sheaths and ridges might be two evolutionary solutions to the same biomechanical problem, i.e. to release ascospores irrespective of length from bottle-shaped asci.

Aspergillus cyclooxygenase-like enzymes are associated with prostaglandin production and virulence

Oxylipins comprise a family of oxygenated fatty acid-derived signaling molecules that initiate critical biological activities in animals, plants, and fungi. Mammalian oxylipins, including the prostaglandins (PGs), mediate many immune and inflammation responses in animals. PG production by pathogenic microbes is theorized to play a role in pathogenesis. We have genetically characterized three Aspergillus genes, ppoA, ppoB, and ppoC, encoding fatty acid oxygenases similar in sequence to specific mammalian prostaglandin synthases, the cyclooxygenases. Enzyme-linked immunosorbent assay analysis showed that production of PG species is decreased in both Aspergillus nidulans and A. fumigatus ppo mutants, implicating Ppo activity in generating PGs. The A. fumigatus triple-ppo-silenced mutant was hypervirulent in the invasive pulmonary aspergillosis murine model system and showed increased tolerance to H(2)O(2) stress relative to that of the wild type. We propose that Ppo products, PG, and/or other oxylipins may serve as activators of mammalian immune responses contributing to enhanced resistance to opportunistic fungi and as factors that modulate fungal development contributing to resistance to host defenses.