Mannitol is essential for the development of stress-resistant ascospores in Neosartorya fischeri (Aspergillus fischeri)

The role of food preservatives in shaping metabolic profile and chemical sensitivity of fungi - an extensive study on crucial mycological food contaminants from the genus Neosartorya (Aspergillus spp.)

Food preservatives are crucial in fruit production, but fungal resistance is a challenge. The main objective was to compare the sensitivity of Neosartorya spp. isolates to preservatives used in food security applications and to assess the role of metabolic properties in shaping Neosartorya spp. resistance. Sodium metabisulfite, potassium sorbate, sodium bisulfite and sorbic acid showed inhibitory effects, with sodium metabisulfite the most effective. Tested metabolic profiles included fungal growth intensity and utilization of amines and amides, amino acids, polymers, carbohydrates and carboxylic acids. Significant decreases in the utilization of all tested organic compound guilds were observed after fungal exposure to food preservatives compared to the control. Although the current investigation was limited in the number of predominately carbohydrate substrates and the breadth of metabolic responses, extensive sensitivity panels are logical step in establishing a course of action against spoilage agents in food production being important approach for innovative food chemistry.

Mannitol mediates the mummification behavior of Thitarodes xiaojinensis larvae infected with Ophiocordyceps sinensis

Introduction

Parasites can facilitate their own spread and reproduction by manipulating insect hosts behavior, as seen in the interaction between Thitarodes xiaojinensis and Ophiocordyceps sinensis. Infection by O. sinensis leads to the mummification of T. xiaojinensis larvae, but the underlying mechanisms remain mysterious.

Methods

The morphology of O. sinensis infected larvae and fungal growth were first observed. Subsequently, the metabolite changes in the larvae before and after infection with the fungus were analyzed by LC/MS and targeted metabolomics. The expression of mannitol-related genes was detected using RT-qPCR, and morphological changes in larvae were observed after injection of different concentrations of mannitol into the O. sinensis-infected larvae.

Results

Significant changes were found in phenotype, fungal morphology in hemocoel, larval hardness, and mannitol metabolites in infected, mummified 0 h larvae and larvae 5 days after mummification behavior. Surprisingly, the occurrence of mummification behavior was accompanied by fungal dimorphism, as well as the absence of mannitol in both infected and non-infected larvae, until the initial accumulation of mannitol and the expression of mannitol-associated genes occurred at the time of mummification behavior. The presence of mannitol may promote fungal dimorphism to mediate changes in fungal toxicity or resistance, leading to the end of the fungus-insect coexistence period and the incidence of mummification behavior. Furthermore, mannitol injections increase the mummification rate of the infected larvae without significant difference from the normal mummification phenotype.

Discussion

This finding suggests the importance of mannitol in the mummification of host larvae infected with O. sinensis.

Comprehensive antifungal investigation of natural plant extracts against Neosartorya spp. (Aspergillus spp.) of agriculturally significant microbiological contaminants and shaping their metabolic profile

Fungi belonging to the genus Neosartorya (teleomorph of Aspergillus spp.) are of great concern in the production and storage of berries and fruit-based products, mainly due to the production of thermoresistant ascospores that cause food spoilage and possible secretion of mycotoxins. We initially tested the antifungal effect of six natural extracts against 20 isolates of Neosartorya spp. using a traditional inhibition test on Petri dishes. Tested isolates did not respond uniformly, creating 5 groups of descending sensitivity. Ten isolates best representing of the established sensitivity clusters were chosen for further investigation using a Biolog™ MT2 microplate assay with the same 6 natural extracts. Additionally, to test for metabolic profile changes, we used a Biolog™ FF microplate assay after pre-incubation with marigold extract. All natural extracts had an inhibitory effect on Neosartorya spp. growth and impacted its metabolism. Lavender and tea tree oil extracts at a concentration of 1000 µg mL-1 presented the strongest antifungal effect during the inhibition test, however all extracts exhibited inhibitory properties at even the lowest dose (5 µg mL-1). The fungal stress response in the presence of marigold extract was characterized by a decrease of amino acids and carbohydrates consumption and an uptake of carboxylic acids on the FF microplates, where the 10 studied isolates also presented differences in their innate resilience, creating 3 distinctive sensitivity groups of high, average and low sensitivity. The results confirm that natural plant extracts and essential oils inhibit and alter the growth and metabolism of Neosartorya spp. suggesting a possible future use in sustainable agriculture as an alternative to chemical fungicides used in traditional crop protection.

Integrated Comparative Transcriptome and Weighted Gene Co-Expression Network Analysis Provide Valuable Insights into the Mechanisms of Pinhead Initiation in Chinese Caterpillar Mushroom Ophiocordyceps sinensis (Ascomycota)

The initiation and formation of the "pinhead" is the key node in growth process of Ophiocordyceps sinensis (Chinese Cordyceps). The research on the mechanism of changes in this growth stage is the basis for realizing the industrialization of its artificial cultivation. Clarifying the mechanisms of pinhead initiation is essential for its further application. Here, we performed a comprehensive transcriptome analysis of pinhead initiation process in O. sinensis. Comparative transcriptome analysis revealed remarkable variation in gene expression and enriched pathways at different pinhead initiation stages. Gene co-expression network analysis by WGCNA identified 4 modules highly relevant to different pinhead initiation stages, and 23 hub genes. The biological function analysis and hub gene annotation of these identified modules demonstrated that transmembrane transport and nucleotide excision repair were the topmost enriched in pre-pinhead initiation stage, carbohydrate metabolism and protein glycosylation were specially enriched in pinhead initiation stage, nucleotide binding and DNA metabolic process were over-represented after pinhead stage. These key regulators are mainly involved in carbohydrate metabolism, synthesis of proteins and nucleic acids. This work excavated the candidate pathways and hub genes related to the pinhead initiation stage, which will serve as a reference for realizing the industrialization of artificial cultivation in O. sinensis.

Mining of Minor Disease Resistance Genes in V. vinifera Grapes Based on Transcriptome

Intraspecific recurrent selection in V. vinifera is an effective method for grape breeding with high quality and disease resistance. The core theory of this method is the substitution accumulation of multi-genes with low disease resistance. The discovery of multi-genes for disease resistance in V. vinifera may provide a molecular basis for breeding for disease resistance in V. vinifera. In this study, resistance to downy mildew was identified, and genetic analysis was carried out in the intraspecific crossing population of V. vinifera (Ecolly × Dunkelfelder) to screen immune, highly resistant and disease-resistant plant samples; transcriptome sequencing and differential expression analysis were performed using high-throughput sequencing. The results showed that there were 546 differential genes (194 up-regulated and 352 down-regulated) in the immune group compared to the highly resistant group, and 199 differential genes (50 up-regulated and 149 down-regulated) in the highly resistant group compared to the resistant group, there were 103 differential genes (54 up-regulated and 49 down-regulated) in the immune group compared to the resistant group. KEGG analysis of differentially expressed genes in the immune versus high-resistance group. The pathway is mainly concentrated in phenylpropanoid biosynthesis, starch and sucrose metabolism, MAPK signaling pathway-plant, carotenoid biosyn-thesis and isoquinoline alkaloid biosynthesis. The differential gene functions of immune and resistant, high-resistant and resistant combinations were mainly enriched in plant-pathogen interaction pathway. Through the analysis of disease resistance-related genes in each pathway, the potential minor resistance genes in V. vinifera were mined, and the accumulation of minor resistance genes was analyzed from the molecular level.

Transcriptome and metabonomics combined analysis revealed the energy supply mechanism involved in fruiting body initiation in Chinese cordyceps

Chinese cordyceps was one of most valuable traditional Chinese medicine fungi. To elucidate the molecular mechanisms related to energy supply mechanism involved in the initiation and formation of primordium in Chinese cordyceps, we performed the integrated metabolomic and transcriptomic analyses of it at pre-primordium period, primordium germination period and after-primordium period, respectively. Transcriptome analysis showed that many genes related to 'starch and sucrose metabolism', 'fructose and mannose metabolism', 'linoleic acid metabolism', 'fatty acids degradation' and 'glycerophospholipid metabolism' were highly up-regulated at primordium germination period. Metabolomic analysis showed many metabolites regulated by these genes in these metabolism pathways were also markedly accumulated at this period. Consequently, we inferred that carbohydrate metabolism and β-oxidation pathway of palmitic acid and linoleic acid worked cooperatively to generate enough acyl-CoA, and then entered TCA cycle to provide energy for fruiting body initiation. Overall, our finding provided important information for further exploring the energy metabolic mechanisms of realizing the industrialization of Chinese cordyceps artificial cultivation.

Description of Two Fungal Endophytes Isolated from Fragaria chiloensis subsp. chiloensis f. patagonica: Coniochaeta fragariicola sp. nov. and a New Record of Coniochaeta hansenii

Prospection of the endosphere of the native plant Fragaria chiloensis subsp. chiloensis f. patagonica from the foothills of the Chilean Andes led to the isolation of two strains of the genus Coniochaeta. We addressed the taxonomic placement of these strains based on DNA sequencing data using the ITS and LSU genetic markers, morphological features, and biochemical traits. One of these strains was identified as Coniochaeta hansenii, for which the anamorph and teleomorph states were described. The second strain did not seem to match any of the currently described species of this genus; therefore, we propose the name Coniochaeta fragariicola sp. nov.

Antifungal metabolites, their novel sources, and targets to combat drug resistance

Excessive antibiotic prescriptions as well as their misuse in agriculture are the main causes of antimicrobial resistance which poses a growing threat to public health. It necessitates the search for novel chemicals to combat drug resistance. Since ancient times, naturally occurring medicines have been employed and the enormous variety of bioactive chemicals found in nature has long served as an inspiration for researchers looking for possible therapeutics. Secondary metabolites from microorganisms, particularly those from actinomycetes, have made it incredibly easy to find new molecules. Different actinomycetes species account for more than 70% of naturally generated antibiotics currently used in medicine, and they also produce a variety of secondary metabolites, including pigments, enzymes, and anti-inflammatory compounds. They continue to be a crucial source of fresh chemical diversity and a crucial component of drug discovery. This review summarizes some uncommon sources of antifungal metabolites and highlights the importance of further research on these unusual habitats as a source of novel antimicrobial molecules.

Current Practices for Reference Gene Selection in RT-qPCR of Aspergillus: Outlook and Recommendations for the Future

Aspergillus is a genus of filamentous fungi with vast geographic and ecological distributions. Species within this genus are clinically, agriculturally and biotechnologically relevant, leading to increasing interest in elucidating gene expression dynamics of key metabolic and physiological processes. Reverse-transcription quantitative Polymerase Chain Reaction (RT-qPCR) is a sensitive and specific method of quantifying gene expression. A crucial step for comparing RT-qPCR results between strains and experimental conditions is normalisation to experimentally validated reference gene(s). In this review, we provide a critical analysis of current reference gene selection and validation practices for RT-qPCR gene expression analyses of Aspergillus. Of 90 primary research articles obtained through our PubMed query, 17 experimentally validated the reference gene(s) used. Twenty reference genes were used across the 90 studies, with beta-tubulin being the most used reference gene, followed by actin, 18S rRNA and glyceraldehyde 3-phosphate dehydrogenase. Sixteen of the 90 studies used multiple reference genes for normalisation. Failing to experimentally validate the stability of reference genes can lead to conflicting results, as was the case for four studies. Overall, our review highlights the need to experimentally validate reference genes in RT-qPCR studies of Aspergillus.

Mannitol-1-phosphate dehydrogenase, MpdA, is required for mannitol production in vegetative cells and involved in hyphal branching, heat resistance of conidia and sexual development in Aspergillus nidulans

Aspergillus nidulans produces cleistothecia as sexual reproductive organs in a process affected by genetic and external factors. To gain a deeper insight into A. nidulans sexual development, we performed comparative proteome analyses based on the wild type developmental periods. We identified sexual development-specific proteins with a more than twofold increase in production during hypoxia or the sexual period compared to the asexual period. Among the sexual development-specific proteins analyzed by gene-deletion experiments and functional assays, MpdA, a putative mannitol-1-phosphate 5-dehydrogenase, plays multiple roles in growth and differentiation of A. nidulans. The most distinct mpdA-deletion phenotype was ascosporogenesis failure. Genetic mpdA deletion resulted in small cleistothecia with no functional ascospores. Transcriptional analyses indicated that MpdA modulates the expression of key development- and meiosis-regulatory genes during sexual development. The mpdA deletion increased hyphal branching and decreased conidial heat resistance. Mannitol production in conidia showed no difference, whereas it was decreased in mycelia and sexual cultures. Addition of mannitol during vegetative growth recovered the defects in conidial heat resistance and ascospore genesis. Taken together, these results indicate that MpdA plays an important role in sexual development, hyphal branching, and conidial heat resistance in Aspergillus nidulans.

Targeting Unconventional Pathways in Pursuit of Novel Antifungals

The impact of invasive fungal infections on human health is a serious, but largely overlooked, public health issue. Commonly affecting the immunocompromised community, fungal infections are predominantly caused by species of Candida, Cryptococcus, and Aspergillus. Treatments are reliant on the aggressive use of pre-existing antifungal drug classes that target the fungal cell wall and membrane. Despite their frequent use, these drugs are subject to unfavorable drug-drug interactions, can cause undesirable side-effects and have compromised efficacy due to the emergence of antifungal resistance. Hence, there is a clear need to develop novel classes of antifungal drugs. A promising approach involves exploiting the metabolic needs of fungi by targeted interruption of essential metabolic pathways. This review highlights potential antifungal targets including enolase, a component of the enolase-plasminogen complex, and enzymes from the mannitol biosynthesis and purine nucleotide biosynthesis pathways. There has been increased interest in the enzymes that comprise these particular pathways and further investigation into their merits as antifungal targets and roles in fungal survival and virulence are warranted. Disruption of these vital processes by targeting unconventional pathways with small molecules or antibodies may serve as a promising approach to discovering novel classes of antifungals.

Effects of high-pressure processing on fungi spores: Factors affecting spore germination and inactivation and impact on ultrastructure

Food contamination with heat-resistant fungi (HRF), and their spores, is a major issue among fruit processors, being frequently found in fruit juices and concentrates, among other products, leading to considerable economic losses and food safety issues. Several strategies were developed to minimize the contamination with HRF, with improvements from harvesting to the final product, including sanitizers and new processing techniques. Considering consumers' demands for minimally processed, fresh-like food products, nonthermal food-processing technologies, such as high-pressure processing (HPP), among others, are emerging as alternatives to the conventional thermal processing techniques. As no heat is applied to foods, vitamins, proteins, aromas, and taste are better kept when compared to thermal processes. Nevertheless, HPP is only able to destroy pathogenic and spoilage vegetative microorganisms to levels of pertinence for food safety, while bacterial spores remain. Regarding HRF spores (both ascospores and conidiospores), these seem to be more pressure-sensible than bacterial spores, despite a few cases, such as the ascospores of Byssochlamys spp., Neosartorya spp., and Talaromyces spp. that are resistant to high pressures and high temperatures, requiring the combination of both variables to be inactivated. This review aims to cover the literature available concerning the effects of HPP at room-like temperatures, and its combination with high temperatures, and high-pressure cycling, to inactivate fungi spores, including the main factors affecting spores' resistance to high-pressure, such as pH, water activity, nutritional composition of the food matrix and ascospore age, as well as the changes in the spore ultrastructure, and the parameters to consider regarding their inactivation by HPP.

Using osmotic stress to stabilize mannitol production in Synechocystis sp. PCC6803

BACKGROUND

Mannitol is a C(6) polyol that is used in the food and medical sector as a sweetener and antioxidant, respectively. The sustainable production of mannitol, especially via the direct conversion of CO₂ by photosynthetic cyanobacteria, has become increasingly appealing. However, previous work aiming to achieve mannitol production in the marine Synechococcus sp. PCC7002 via heterologous expression of mannitol-1-phosphate-5-dehydrogenase (mtlD) and mannitol-1-phosphatase (m1p, in short: a 'mannitol cassette'), proved to be genetically unstable. In this study, we aim to overcome this genetic instability by conceiving a strategy to stabilize mannitol production using Synechocystis sp. PCC6803 as a model cyanobacterium.

RESULTS

Here, we explore the stabilizing effect that mannitol production may have on cells faced with osmotic stress, in the freshwater cyanobacterium Synechocystis sp. PCC6803. We first validated that mannitol can function as a compatible solute in Synechocystis sp. PCC6803, and in derivative strains in which the ability to produce one or both of the native compatible solutes was impaired. Wild-type Synechocystis, complemented with a mannitol cassette, indeed showed increased salt tolerance, which was even more evident in Synechocystis strains in which the ability to synthesize the endogenous compatible solutes was impaired. Next we tested the genetic stability of all these strains with respect to their mannitol productivity, with and without salt stress, during prolonged turbidostat cultivations. The obtained results show that mannitol production under salt stress conditions in the Synechocystis strain that cannot synthesize its endogenous compatible solutes is remarkably stable, while the control strain completely loses this ability in only 6 days. DNA sequencing results of the control groups that lost the ability to synthesize mannitol revealed that multiple types of mutation occurred in the mtlD gene that can explain the disruption of mannitol production.

CONCLUSIONS

Mannitol production in freshwater Synechocsytis sp. PCC6803 confers it with increased salt tolerance. Under this strategy, genetically instability which was the major challenge for mannitol production in cyanobacteria is tackled. This paper marks the first report of utilization of the response to salt stress as a factor that can increase the stability of mannitol production in a cyanobacterial cell factory.

Aspergillus fumigatus and Aspergillosis in 2019

Aspergillus fumigatus is a saprotrophic fungus; its primary habitat is the soil. In its ecological niche, the fungus has learned how to adapt and proliferate in hostile environments. This capacity has helped the fungus to resist and survive against human host defenses and, further, to be responsible for one of the most devastating lung infections in terms of morbidity and mortality. In this review, we will provide (i) a description of the biological cycle of A. fumigatus; (ii) a historical perspective of the spectrum of aspergillus disease and the current epidemiological status of these infections; (iii) an analysis of the modes of immune response against Aspergillus in immunocompetent and immunocompromised patients; (iv) an understanding of the pathways responsible for fungal virulence and their host molecular targets, with a specific focus on the cell wall; (v) the current status of the diagnosis of different clinical syndromes; and (vi) an overview of the available antifungal armamentarium and the therapeutic strategies in the clinical context. In addition, the emergence of new concepts, such as nutritional immunity and the integration and rewiring of multiple fungal metabolic activities occurring during lung invasion, has helped us to redefine the opportunistic pathogenesis of A. fumigatus.

Molecular Mechanisms of Conidial Germination in Aspergillus spp

Aspergilli produce conidia for reproduction or to survive hostile conditions, and they are highly effective in the distribution of conidia through the environment. In immunocompromised individuals, inhaled conidia can germinate inside the respiratory tract, which may result in invasive pulmonary aspergillosis. The management of invasive aspergillosis has become more complex, with new risk groups being identified and the emergence of antifungal resistance. Patient survival is threatened by these developments, stressing the need for alternative therapeutic strategies. As germination is crucial for infection, prevention of this process might be a feasible approach. A broader understanding of conidial germination is important to identify novel antigermination targets. In this review, we describe conidial resistance against various stresses, transition from dormant conidia to hyphal growth, the underlying molecular mechanisms involved in germination of the most common Aspergillus species, and promising antigermination targets. Germination of Aspergillus is characterized by three morphotypes: dormancy, isotropic growth, and polarized growth. Intra- and extracellular proteins play an important role in the protection against unfavorable environmental conditions. Isotropically expanding conidia remodel the cell wall, and biosynthetic machineries are needed for cellular growth. These biosynthetic machineries are also important during polarized growth, together with tip formation and the cell cycle machinery. Genes involved in isotropic and polarized growth could be effective antigermination targets. Transcriptomic and proteomic studies on specific Aspergillus morphotypes will improve our understanding of the germination process and allow discovery of novel antigermination targets and biomarkers for early diagnosis and therapy.

A New Pathway for Mannitol Metabolism in Yeasts Suggests a Link to the Evolution of Alcoholic Fermentation

The yeasts belonging to the Wickerhamiella and Starmerella genera (W/S clade) share a distinctive evolutionary history marked by loss and subsequent reinstatement of alcoholic fermentation mediated by horizontal gene transfer events. Species in this clade also share unusual features of metabolism, namely the preference for fructose over glucose as carbon source, a rare trait known as fructophily. Here we show that fructose may be the preferred sugar in W/S-clade species because, unlike glucose, it can be converted directly to mannitol in a reaction with impact on redox balance. According to our results, mannitol is excreted to the growth medium in appreciable amounts along with other fermentation products such as glycerol and ethanol but unlike the latter metabolites mannitol production increases with temperature. We used comparative genomics to find genes involved in mannitol metabolism and established the mannitol biosynthesis pathway in W/S-clade species Starmerella bombicola using molecular genetics tools. Surprisingly, mannitol production seems to be so important that St. bombicola (and other W/S-clade species) deploys a novel pathway to mediate the conversion of glucose to fructose, thereby allowing cells to produce mannitol even when glucose is the sole carbon source. Using targeted mutations and ¹³C-labeled glucose followed by NMR analysis of end-products, we showed that the novel mannitol biosynthesis pathway involves fructose-6-phosphate as an intermediate, implying a key role for a yet unknown fructose-6-P phosphatase. We hypothesize that mannitol production contributed to mitigate the negative effects on redox balance of the ancient loss of alcoholic fermentation in the W/S clade. Presently, mannitol also seems to play a role in stress protection.

Characterizing the Pathogenic, Genomic, and Chemical Traits of Aspergillus fischeri, a Close Relative of the Major Human Fungal Pathogen Aspergillus fumigatus

Aspergillus fischeri is closely related to Aspergillus fumigatus, the major cause of invasive mold infections. Even though A. fischeri is commonly found in diverse environments, including hospitals, it rarely causes invasive disease. Why A. fischeri causes less human disease than A. fumigatus is unclear. A comparison of A. fischeri and A. fumigatus for pathogenic, genomic, and secondary metabolic traits revealed multiple differences in pathogenesis-related phenotypes. We observed that A. fischeri NRRL 181 is less virulent than A. fumigatus strain CEA10 in multiple animal models of disease, grows slower in low-oxygen environments, and is more sensitive to oxidative stress. Strikingly, the observed differences for some traits are of the same order of magnitude as those previously reported between A. fumigatus strains. In contrast, similar to what has previously been reported, the two species exhibit high genomic similarity; ∼90% of the A. fumigatus proteome is conserved in A. fischeri, including 48/49 genes known to be involved in A. fumigatus virulence. However, only 10/33 A. fumigatus biosynthetic gene clusters (BGCs) likely involved in secondary metabolite production are conserved in A. fischeri and only 13/48 A. fischeri BGCs are conserved in A. fumigatus Detailed chemical characterization of A. fischeri cultures grown on multiple substrates identified multiple secondary metabolites, including two new compounds and one never before isolated as a natural product. Additionally, an A. fischeri deletion mutant of laeA, a master regulator of secondary metabolism, produced fewer secondary metabolites and in lower quantities, suggesting that regulation of secondary metabolism is at least partially conserved. These results suggest that the nonpathogenic A. fischeri possesses many of the genes important for A. fumigatus pathogenicity but is divergent with respect to its ability to thrive under host-relevant conditions and its secondary metabolism.IMPORTANCEAspergillus fumigatus is the primary cause of aspergillosis, a devastating ensemble of diseases associated with severe morbidity and mortality worldwide. A. fischeri is a close relative of A. fumigatus but is not generally observed to cause human disease. To gain insights into the underlying causes of this remarkable difference in pathogenicity, we compared two representative strains (one from each species) for a range of pathogenesis-relevant biological and chemical characteristics. We found that disease progression in multiple A. fischeri mouse models was slower and caused less mortality than A. fumigatus Remarkably, the observed differences between A. fischeri and A. fumigatus strains examined here closely resembled those previously described for two commonly studied A. fumigatus strains, AF293 and CEA10. A. fischeri and A. fumigatus exhibited different growth profiles when placed in a range of stress-inducing conditions encountered during infection, such as low levels of oxygen and the presence of chemicals that induce the production of reactive oxygen species. We also found that the vast majority of A. fumigatus genes known to be involved in virulence are conserved in A. fischeri, whereas the two species differ significantly in their secondary metabolic pathways. These similarities and differences that we report here are the first step toward understanding the evolutionary origin of a major fungal pathogen.

Response of Paracoccidioides lutzii to the antifungal camphene thiosemicarbazide determined by proteomic analysis

Aim: To perform the proteomic profile of Paracoccidioides lutzii after treatment with the compound camphene thiosemicarbazide (TSC-C) in order to study its mode of action. Methods: Proteomic analysis was carried out after cells were incubated with TSC-C in a subinhibitory concentration. Validation of the proteomic results comprised the azocasein assay, western blot and determination of the susceptibility of a mutant to the compound. Results: Proteins related to metabolism, energy and protein fate were regulated after treatment. In addition, TSC-C reduces the proteolytic activity of the protein extract similarly to different types of protease inhibitors. Conclusion: TSC-C showed encouraging antifungal activity, working as a protease inhibitor and downregulating important pathways impairing the ability of the fungi cells to produce important precursors.

Dysregulated gliotoxin biosynthesis attenuates the production of unrelated biosynthetic gene cluster-encoded metabolites in Aspergillus fumigatus

Gliotoxin is an epipolythiodioxopiperazine (ETP) class toxin, contains a disulfide bridge that mediates its toxic effects via redox cycling and is produced by the opportunistic fungal pathogen Aspergillus fumigatus. The gliotoxin bis-thiomethyltransferase, GtmA, attenuates gliotoxin biosynthesis in A. fumigatus by conversion of dithiol gliotoxin to bis-thiomethylgliotoxin (BmGT). Here we show that disruption of dithiol gliotoxin bis-thiomethylation functionality in A. fumigatus results in significant remodelling of the A. fumigatus secondary metabolome upon extended culture. RP-HPLC and LC-MS/MS analysis revealed the reduced production of a plethora of unrelated biosynthetic gene cluster-encoded metabolites, including pseurotin A, fumagillin, fumitremorgin C and tryprostatin B, occurs in A. fumigatus ΔgtmA upon extended incubation. Parallel quantitative proteomic analysis of A. fumigatus wild-type and ΔgtmA during extended culture revealed cognate abundance alteration of proteins encoded by relevant biosynthetic gene clusters, allied to multiple alterations in hypoxia-related proteins. The data presented herein reveal a previously concealed functionality of GtmA in facilitating the biosynthesis of other BGC-encoded metabolites produced by A. fumigatus.

Mannitol metabolism during pathogenic fungal-host interactions under stressed conditions

Numerous plants and fungi produce mannitol, which may serve as an osmolyte or metabolic store; furthermore, mannitol also acts as a powerful quencher of reactive oxygen species (ROS). Some phytopathogenic fungi use mannitol to stifle ROS-mediated plant resistance. Mannitol is essential in pathogenesis to balance cell reinforcements produced by both plants and animals. Mannitol likewise serves as a source of reducing power, managing coenzymes, and controlling cytoplasmic pH by going about as a sink or hotspot for protons. The metabolic pathways for mannitol biosynthesis and catabolism have been characterized in filamentous fungi by direct diminishment of fructose-6-phosphate into mannitol-1-phosphate including a mannitol-1-phosphate phosphatase catalyst. In plants mannitol is integrated from mannose-6-phosphate to mannitol-1-phosphate, which then dephosphorylates to mannitol. The enzyme mannitol dehydrogenase plays a key role in host–pathogen interactions and must be co-localized with pathogen-secreted mannitol to resist the infection.

A decrease in bulk water and mannitol and accumulation of trehalose and trehalose-based oligosaccharides define a two-stage maturation process towards extreme stress resistance in ascospores of Neosartorya fischeri (Aspergillus fischeri)

Fungal propagules survive stresses better than vegetative cells. Neosartorya fischeri, an Aspergillus teleomorph, forms ascospores that survive high temperatures or drying followed by heat. Not much is known about maturation and development of extreme stress resistance in fungal cells. This study provides a novel two-step model for the acquisition of extreme stress resistance and entry into dormancy. Ascospores of 11- and 15-day-old cultures exhibited heat resistance, physiological activity, accumulation of compatible solutes and a steep increase in cytoplasmic viscosity. Electron spin resonance spectroscopy indicated that this stage is associated with the removal of bulk water and an increase of chemical stability. Older ascospores from 15- to 50-day-old cultures showed no changes in compatible solute content and cytoplasmic viscosity, but did exhibit a further increase of heat resistance and redox stability with age. This stage was also characterized by changes in the composition of the mixture of compatible solutes. Mannitol levels decreased and the relative quantities of trehalose and trehalose-based oligosaccharides increased. Dormant ascospores of N. fischeri survive in low-water habitats. After activation of the germination process, the stress resistance decreases, compatible solutes are degraded and the cellular viscosity drops. After 5 h, the hydrated cells enter the vegetative stage and redox stability has decreased notably.