Macro-micro exploration on dynamic interaction between aflatoxigenic Aspergillus flavus and maize kernels using Vis/NIR hyperspectral imaging and SEM technology

Aspergillus flavus and its toxic metabolites-aflatoxins infect and contaminate maize kernels, posing a threat to grain safety and human health. Due to the complexity of microbial growth and metabolic processes, dynamic mechanisms among fungal growth, nutrient depletion of maize kernels and aflatoxin production is still unclear. In this study, visible/near infrared (Vis/NIR) hyperspectral imaging (HSI) combined with the scanning electron microscope (SEM) was used to elucidate the critical organismal interaction at kernel (macro-) and microscopic levels. As kernel damage is the main entrance for fungal invasion, maize kernels with gradually aggravated damages from intact to pierced to halved kernels with A. flavus were cultured for 0-120 h. The spectral fingerprints of the A. flavus-maize kernel complex over time were analyzed with principal components analysis (PCA) of hyperspectral images, where the pseudo-color score maps and the loading plots of the first three PCs were used to investigate the dynamic process of fungal infection and to capture the subtle changes in the complex with different hardness of the maize matrix. The dynamic growth process of A. flavus and the interactions of fungus-maize complexes were explained on a microscopic level using SEM. Specifically, fungus morphology, e.g., hyphae, conidia, and conidiophore (stipe) was accurately captured on the microscopic level, and the interaction process between A. flavus and nutrient loss from the maize kernel tissues (i.e., embryo, and endosperm) was described. Furthermore, the growth stage discrimination models based on PLSDA with the results of CCRC = 100 %, CCRV = 97 %, CCRIV = 93 %, and the prediction models of AFB1 based on PLSR with satisfactory performance (R2C = 0.96, R2V = 0.95, R2IV = 0.93 and RPD = 3.58) were both achieved. In conclusion, the results from both macro-level (Vis/NIR-HSI) and micro-level (SEM) assessments revealed the dynamic organismal interactions in A. flavus-maize kernel complex, and the detailed data could be used for modeling, and quantitative prediction of aflatoxin, which would establish a theoretical foundation for the early detection of fungal or toxin contaminated grains to ensure food security.

Phytochemicals reduced growth, sporulation and conidial dimensions of Fusarium verticillioides, cause of fumonisin contamination in maize grains

The objective of the study was to evaluate the effectiveness of methanolic extracts of plants against radial growth and spore dimensions of Fusarium verticillioides. Leaf extracts of 25 plants were tested against the fungus. Of which, thirteen extracts were potent against the fungus and evaluated using food poising technique. Growth was evaluated on PDA medium amended with the extracts at 5 mg ml-1. Control treatments included plates without (negative) extracts and with synthetic (positive) fungicide. Spore dimension was determined using PDB. The results showed T. vulgaris extract completely inhibited mycelial growth of the fungus as equivalent as the fungicide. Similarly, G. parviflora, C. citratus, R. officinalis, R. chalepensis, and Agave sp. also recorded growth reductions ranging from 71.04 to 81.35 % at day seven. In addition, extracts of Agave sp., C. citratus and T. vulgaris did not support sporulation. Overall, the results indicate that T. vulgaris extracts could be safe source of bioactive chemicals to control F. verticillioides.

Analysis of the emerging physical network in young mycelia

Filamentous fungi develop intricate hyphal networks that support mycelial foraging and transport of resources. These networks have been analyzed recently using graph theory, enabling the development of models that seek to predict functional traits. However, attention has focused mainly on mature colonies. Here, we report the extraction and analysis of the graph corresponding to Trichoderma atroviride mycelia only a few hours after conidia germination. To extract the graph for a given mycelium, a mosaic conformed of multiple bright-field, optical microscopy images is digitally processed using freely available software. The resulting graphs are characterized in terms of number of nodes and edges, average edge length, total mycelium length, hyphal growth unit, maximum edge length and mycelium diameter, for colonies between 8 h and 14 h after conidium germination. Our results show that the emerging hyphal network grows first by hyphal elongation and branching, and then it transitions to a stage where hyphal-hyphal interactions become significant. As a tangled hyphal network develops with decreasing hyphal mean length, the mycelium maintains long (∼2 mm) hyphae-a behavior that suggests a combination of aggregated and dispersed architectures to support foraging. Lastly, analysis of early network development in Podospora anserina reveals striking similarity with T. atroviride, suggesting common mechanisms during initial colony formation in filamentous fungi.

A layered solid-state culture system for investigating the fungal growth and decay behaviour on the cellulosic substrate

Mycelium-based materials have attracted growing interest, facilitating their development for various new applications. Finding for suitable fungal species and strains enables further technical breakthroughs in their development and quality control. Here, we developed a model solid-state culture system to screen fungal strains efficiently for mycelium-based materials production. A piece of silicone-coated paper set on the general agar plate allows for isolation of the mycelial mat from the substrate. The mycelial growth and density can be evaluated by weighing the mycelial mat. We used the paper substrate after fungal incubation to investigate the relationship between substrate degradation and the contact time with hyphae. It yielded further insights into the fungal decay. Ten basidiomycetes were assessed for their fungal growth and degradation behaviour of the substrate using this method. Pleurotus floridanus FBCC375 showed a dense and elastic mycelial mat and mild degradation of the substrate. A unique decay behaviour was found in Hypsizygus ulmarius FBCC573 and Trametes versicolor FBCC564. They indicated a positional imbalance in the decay activity within the colony. This simple method is helpful for screening fungal strains and facilitates the further development of mycelium-based materials.

Interactions among mycorrhizal fungi enhance the early development of a Mediterranean orchid

Orchids depend on mycorrhizal fungi to germinate from seed. While multiple orchid mycorrhizal (OrM) taxa are often found associated with adult orchids, the relative contribution of particular OrM taxa to germination and early orchid development is poorly understood. We isolated 28 OrM fungi associated with the Mediterranean orchid Anacamptis papilionacea and tested the efficiency of five isolates on germination and early development, four belonging to the Tulasnella calospora species complex and one belonging to Ceratobasidium. Co-cultures of varying two-way and three-way combinations of OrM isolates were used in vitro to compare the simultaneous effect on seed germination rate with monocultures. We then tested whether, when given initial priority over other fungi, particular OrM taxa were more effective during the early stages of development. Seedlings germinated with different isolates were transferred to a growth chamber, and either the same or different isolate was added 45 days later. After 3 months, the number of roots, length of the longest root, and tuber area were measured. All OrM fungi resulted in seed germination; however, lower germination rates were associated with the Ceratobasidium isolate compared to the tulasnelloid isolates. There was significant decreased germination in co-culture experiments when the Ceratobasidium isolate was added. Despite being associated with reduced germination rates, the addition of the Ceratobasidium isolate to the seedlings germinated with tulasnelloid strains resulted in significant increased tuber size. Although A. papilionacea associates with many OrM taxa, these results show that OrM fungi may play different roles during orchid germination and early development. Even when given initial priority, other fungi may colonize developing orchids and interact to influence early orchid development.

Utilization of fleshing waste of leather processing for the growth of zygomycetes: A new substrate for economical production of bio-polymer chitosan

A simple scalable method has been developed to obtain protein hydrolysate from fleshing waste generated during leather processing. UV-Vis, FTIR and Solid State C¹³ NMR analyses identified that prepared protein hydrolysate is basically collagen hydrolysate. DLS and MALDI-TOF-MS spectra indicated that the prepared protein hydrolysate is mostly comprised of di- and tri-peptides and less poly-dispersed than the standard commercial product. A combination of 0.3% Yeast extract, 1% Protein Hydrolysate (PHz) and 2% Glucose is found to be the most efficient nutrient composition for the fermentative growth of three well-known chitosan producing zygomycetes group of fungi. Mucor sp. showed highest yield of biomass (2.74 g/L) as well as chitosan (335 mg/L). Biomass and chitosan yield for Rhizopus oryzae were found 1.53 g/L; 239 mg/L. Same for Absidia coerulea were 2.05 g/L and 212 mg/L, respectively. This work shows promising prospect of utilization of fleshing waste of leather processing for the low-cost production of industrially important biopolymer chitosan.

The putative methyltransferase LaeA regulates mycelium growth and cellulase production in Myceliophthora thermophila

BACKGROUND

Filamentous fungi with the ability to use complex carbon sources has been developed as platforms for biochemicals production. Myceliophthora thermophila has been developed as the cell factory to produce lignocellulolytic enzymes and plant biomass-based biofuels and biochemicals in biorefinery. However, low fungal growth rate and cellulose utilization efficiency are significant barriers to the satisfactory yield and productivity of target products, which needs our further exploration and improvement.

RESULTS

In this study, we comprehensively explored the roles of the putative methyltransferase LaeA in regulating mycelium growth, sugar consumption, and cellulases expression. Deletion of laeA in thermophile fungus Myceliophthora thermophila enhanced mycelium growth and glucose consumption significantly. Further exploration of LaeA regulatory network indicated that multiple growth regulatory factors (GRF) Cre-1, Grf-1, Grf-2, and Grf-3, which act as negative repressors of carbon metabolism, were regulated by LaeA in this fungus. We also determined that phosphoenolpyruvate carboxykinase (PCK) is the core node of the metabolic network related to fungal vegetative growth, of which enhancement partially contributed to the elevated sugar consumption and fungal growth of mutant ΔlaeA. Noteworthily, LaeA participated in regulating the expression of cellulase genes and their transcription regulator. ΔlaeA exhibited 30.6% and 5.5% increases in the peak values of extracellular protein and endo-glucanase activity, respectively, as compared to the WT strain. Furthermore, the global histone methylation assays indicated that LaeA is associated with modulating H3K9 methylation levels. The normal function of LaeA on regulating fungal physiology is dependent on methyltransferase activity.

CONCLUSIONS

The research presented in this study clarified the function and elucidated the regulatory network of LaeA in the regulation of fungal growth and cellulase production, which will significantly deepen our understanding about the regulation mechanism of LaeA in filamentous fungi and provides the new strategy for improvement the fermentation properties of industrial fungal strain by metabolic engineering.

Tissue Cultivation, Preparation, and Extraction of High Molecular Weight DNA for Single-Molecule Genome Sequencing of Plant-Associated Fungi

Extraction of high-quality, high molecular weight DNA is a critical step for sequencing an organism's genome. For fungi, DNA extraction is often complicated by co-precipitation of secondary metabolites, the most destructive being polysaccharides, polyphenols, and melanin. Different DNA extraction protocols and clean-up methods have been developed to address challenging materials and contaminants; however, the method of fungal cultivation and tissue preparation also plays a critical role to limit the production of inhibitory compounds prior to extraction. Here, we provide protocols and guidelines for (i) fungal tissue cultivation and processing with solid media containing a cellophane overlay or in liquid media, (ii) DNA extraction with customized recommendations for taxonomically and ecologically diverse plant-associated fungi, and (iii) assessing DNA quantity and quality for downstream genome sequencing with single-molecule technology such as PacBio.

The interplays between epigallocatechin-3-gallate (EGCG) and Aspergillus niger RAF106 based on metabolism

Epigallocatechin-3-gallate (EGCG) is a vital kind of catechin with high bioactive activities, however, limited research has been conducted to elucidate the molecular basis of EGCG biotransformation by Aspergillus niger and the underlying regulatory mechanisms. In this study, A. niger RAF106, isolated from Pu-erh tea, was applied to conduct the EGCG fermentation process, and the samples were collected at different fermentation times to determine the intermediary metabolites of EGCG and the metabolome as well as physiological activity changes of A. niger RAF106. The results demonstrated that EGCG enhances the growth of A. niger RAF106 by promoting conidial germination and hyphae branching. Meanwhile, metabolomic analyses indicated that EGCG significantly regulates the amino acid metabolism of A. niger RAF106. Furthermore, metabolomic analyses also revealed that the levels of original secondary metabolites in the supernatant of the cultures changed significantly from the fermentation stage M2 to M3, in which the main differentially changed metabolites (DCMs) were flavonoids. Most of these flavonoids exhibited antioxidant properties and thus increased the radical scavenging activity of the supernatant of the cultures. In addition, we also found several intermediary metabolites of EGCG, GA, and EGC, including oolonghomobisflavan A, (-)-Epigallocatechin 3, 5-di-gallate, (-)-Epigallocatechin 3-(3-methyl-gallate) (-)-Catechin 3-O-gallate, 4'-Methyl-(-)-epigallocatechin 3-(4-methyl-gallate), myricetin, prodelphinidin B, 7-galloylcatechin, and 3-hydroxyphenylacetic acid. These findings contribute to improving the bioavailability of EGCG and help mine highly active metabolites, which can be used as raw materials for the development of pharmaceutical intermediates or functional foods. In addition, the results also provide a theoretical basis for better control of the risk of A. niger origin and the regulatory mechanisms of the biotransformation process mediated by A. niger.

The non-canonical functions of telomerase reverse transcriptase gene GlTert on regulating fungal growth, oxidative stress, and ganoderic acid biosynthesis in Ganoderma lucidum

The telomerase reverse transcriptase (TERT) is the core catalytic subunit of telomerase. Its canonical function is synthesizing telomeric repeats to maintain telomere length and chromosomal stability. Accumulating evidence suggests that TERT has other important fundamental functions in addition to its catalytic telomere repeat synthesis activity. However, the non-canonical roles of TERT independent of its enzymatic activity are not clear in filamentous fungi. In the present study, we characterized the GlTert gene in Ganoderma lucidum. The non-canonical roles of GlTert were explored using GlTert-silenced strains (Terti8 and Terti25) obtained by RNA interference. Silencing GlTert delayed the fungal growth, decreased the length between hyphal branches, and induced fungal resistance to oxidative stress in G. ludicum. Further examination revealed that the intracellular ROS (reactive oxygen species) levels were increased while the enzyme activities of the antioxidant systems (superoxide dismutase, catalase, glutathione peroxidase, and ascorbate peroxidase) were decreased in GlTert-silenced strains. In addition, silencing GlTert decreased the ganoderic acid (GA) biosynthesis of G. lucidum. Taken together, our results indicate that GlTert plays a fundamental function on fungal growth, oxidative stress, and GA biosynthesis in G. lucidum, providing new insights for the canonical functions of TERT in filamentous fungi. KEY POINTS: • GlTert affected fungal growth and hyphal branching of G. lucidum. • Silencing GlTert increased the intracellular ROS levels of G. lucidum. • GlTert regulated GA biosynthesis of G. lucidum.

On the use of n-octyl gallate and salicylhydroxamic acid to study the alternative oxidase role

The alternative oxidase (AOX) catalyzes the transfer of electrons from ubiquinol to oxygen without the translocation of protons across the inner mitochondrial membrane. This enzyme has been proposed to participate in the regulation of cell growth, sporulation, yeast-mycelium transition, resistance to reactive oxygen species, infection, and production of secondary metabolites. Two approaches have been used to evaluate AOX function: incubation of cells for long periods of time with AOX inhibitors or deletion of AOX gene. However, AOX inhibitors might have different targets. To test non-specific effects of n-octyl gallate (nOg) and salicylhydroxamic acid (SHAM) on fungal physiology we measured the growth and respiratory capacity of two fungal strains lacking (Ustilago maydis-Δaox and Saccharomyces cerevisiae) and three species containing the AOX gene (U. maydis WT, Debaryomyces hansenii, and Aspergillus nidulans). For U. maydis, a strong inhibition of growth and respiratory capacity by SHAM was observed, regardless of the presence of AOX. Similarly, A. nidulans mycelial growth was inhibited by low concentrations of nOg independently of AOX expression. In contrast, these inhibitors had no effect or had a minor effect on S. cerevisiae and D. hansenii growth. These results show that nOg and SHAM have AOX independent effects which vary in different microorganisms, indicating that studies based on long-term incubation of cells with these inhibitors should be considered as inconclusive.

Comparison of Cu salts and commercial Cu based fungicides on toxicity towards microorganisms in soil

Microbial responses to Cu pollution as a function of Cu sources (Cu salts and commercial Cu fungicides) were assessed in a soil using basal soil respiration, and bacterial and fungal community growth, as endpoints. The soil was amended with different concentrations (0-32 mmol Cu kg^-1) of Cu nitrate, Cu sulfate, Bordeaux mixture and 3 types of Cu oxychloride. Cu salts decreased soil pH, while this was not found with the other Cu sources. This difference in soil pH effects caused differences in the respiration, bacterial growth and fungal growth response. Basal soil respiration was negatively affected by Cu addition when the soil was spiked with Cu salts, but almost unaffected by commercial Cu fungicides. Bacterial growth was significantly and negatively affected by Cu addition for all the Cu sources, but Cu toxicity was higher for Cu salts than for commercial Cu fungicides. Fungal growth response was also different for Cu salts and commercial Cu fungicides, but only in the long-term. High Cu amendments using Cu salts stimulated fungal growth, whereas for commercial Cu fungicides, these concentrations inhibited fungal growth. Thus, the use of products similar to those used in commercial fungicides is a recommended practice for Cu risk assessments in soil.

The bZIP transcription factor FpAda1 is essential for fungal growth and conidiation in Fusarium pseudograminearum

Fusarium pseudograminearum is an important pathogen of Fusarium crown rot and Fusarium head blight, which is able to infect wheat and barley worldwide, causing great economic losses. Transcription factors (TFs) of the basic leucine zipper (bZIP) protein family control important processes in all eukaryotes. In this study, we identified a gene, designated FpAda1, encoding a bZIP TF in F. pseudograminearum. The homolog of FpAda1 is also known to affect hyphal growth in Neurospora crassa. Deletion of FpAda1 in F. pseudograminearum resulted in defects in hyphal growth, mycelial branching and conidia formation. Pathogenicity assays showed that virulence of the Δfpada1 mutant was dramatically decreased on wheat coleoptiles and barley leaves. However, wheat coleoptile inoculation assay showed that Δfpada1 could penetrate and proliferate in wheat cells. Moreover, the FpAda1 was required for abnormal nuclear morphology in conidia and transcription of FpCdc2 and FpCdc42. Taken together, these results indicate that FpAda1 is an important transcription factor involved in growth and development in F. pseudograminearum.

Mapping haze-komi on rice koji grains using β-glucuronidase expressing Aspergillus oryzae and mass spectrometry imaging

In sake brewing, the quality of rice koji is evaluated by experienced sake brewers based on visual inspection of the haze, which is defined by the extent of fungal hyphae spread on/into the rice grains. There is an increasing interest in understanding the factors that affect the quality of rice koji, which is dependent on its making process. Several studies have focused on the degree of mycelial penetration (haze-komi) and enzyme production during rice koji production. However, there are limited analytical methods available to monitor hyphal growth on a solid surface. Here we used a β-glucuronidase (GUS)-expressing strain of Aspergillus oryzae to visualize and map the fungal growth on rice koji grains. Observation of indigo color revealed that A. oryzae hyphae penetrated the steamed rice grain in the early stage (24 h) of rice koji-making before spreading on the surface during the later stages. Additionally, hyphae penetrated along the endosperm cells and penetrated the cells to form the sou-haze. Furthermore, mass spectrometry imaging (MSI) of glucose demonstrated that the area of mycelial penetration is directly correlated with the spread of glucose during fermentation. This is the first report on utilizing new tools such as GUS-body-mapping of A. oryzae and MSI to monitor fungal growth during rice koji making.

Marine bisindole alkaloid 2,2-bis(6-bromo-3-indolyl)ethylamine to control and prevent fungal growth on building material: a potential antifungal agent

The potential antifungal activity of the marine alkaloid 2,2-bis(6-bromo-3-indolyl)ethylamine (URB 1204) was firstly assessed by minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) against different fungi. Then, URB 1204 was applied to a building material experimentally contaminated with selected fungi, in single and mixed species, for determining its potential application in preventing fungal growth. In addition, the over-time protection efficacy of URB 1204 was verified, subjecting the treated building surfaces to natural fungal contamination for 6 weeks. URB 1204 showed different antifungal activity, with the lowest MIC value (16 μg/mL) observed against Aspergillus flavus IDRA01, Cladosporium cladosporioides ATCC 16022 and Mucor circinelloides EHS03, and the highest MIC (128 μg/mL) against the dermatophytes strains. The growth Alternaria alternata BC01, Penicillium citrinum LS1, and C. cladosporioides ATCC 16022 on building material treated with URB 1204 water solution (64 μg/mL) was remarkably reduced with an effect time-dependent and related to the examined fungi. In terms of over-time efficacy, the samples treated with URB 1204 showed a delay of fungal growth comparable with that of a commercial antifungal product. These findings evidenced not only the ability of 2,2-bis(6-bromo-3-indolyl)ethylamine to limit the growth of different fungal species on building material but also to provide long-term protection against mold growth and proliferation, opening new perspectives for URB 1204 as preventive agent.

Early discrimination and growth tracking of Aspergillus spp. contamination in rice kernels using electronic nose

Early detection of Aspergillus spp. contamination in rice was investigated by electronic nose (E-nose) in this study. Sterilized rice artificially inoculated with three Aspergillus strains were subjected to GC-MS and E-nose analyses. Principle Component Analysis (PCA), Partial Least Squares Regression (PLSR), Back-propagation neural network (BPNN), Support Vector Machine (SVM) and Learning Vector Quantization (LVQ) were employed for qualitative classification and quantitative regression. GC-MS analysis revealed a significant correlation between the volatile compounds and total amounts/species of fungi. While X-axis barycenters of PC1 scores were significantly correlated with fungal counts, logistic model could be employed to simulate the growth of individual fungus (R² = 0.978-0.996). Fungal species and counts in rice could be classified and predicted by BPNN (96.4%) and PLSR (R² = 0.886-0.917), respectively. The results demonstrated that E-nose combined with BPNN might offer the feasibility for early detection of Aspergillus spp. contamination in rice.

Investigating a non-destructive alternative for a preliminary evaluation of fungal growth in solid state fermentations

Solid state fermentation (SSF) is an ancient technique which keeps attracting the attention of the food and biotechnology industries; however, a direct quantification of microbial biomass is still a fundamental challenge in this type of processes. Typically, growth is measured using indirect and destructive methods which do not allow a continuous evaluation of the evolution of microbial biomass within a single system. This article presents a non-destructive, quick and simple technique, based on digital imaging analysis (DIA) for the evaluation of growth in SSF laboratory experiments. DIA uses computational analysis of images from a SSF to measure areas and colour changes on a surface. The method can then be used to monitor microbial growth by assigning quantitative values for the growth of filamentous fungi. Firstly, studies on agar plates are used for the description of the method and to illustrate how it can be used to monitor fungal colony areas and densities. Following that, agro-industrial residues are used to demonstrate the application of the technique. DIA proved to be a practical and inexpensive tool to measure colony areas and densities. Furthermore, it is a non-destructive and non-intrusive method, which means that the evaluation of growth can be achieved within a single system.

Discrimination and growth tracking of fungi contamination in peaches using electronic nose

A non-destructive method for detection of fungal contamination in peaches using an electronic nose (E-nose) is presented. Peaches were inoculated with three common spoilage fungi, Botrytis cinerea, Monilinia fructicola and Rhizopus stolonifer and then stored for various periods. E-nose was then used to analyze volatile compounds generated in the fungi-inoculated peaches, which was then compared with the growth data (colony counts) of the fungi. The results showed that changes in volatile compounds in fungi-inoculated peaches were correlated with total amounts and species of fungi. Terpenes and aromatic compounds were the main contributors to E-nose responses. While principle component analysis (PC1) scores were highly correlated with fungal colony counts, Partial Least Squares Regression (PLSR) could effectively be used to predict fungal colony counts in peach samples. The results also showed that the E-nose had high discrimination accuracy, demonstrating the potential use of E-nose to discriminate among fungal contamination in peaches.

In-host microevolution of Aspergillus fumigatus: A phenotypic and genotypic analysis

In order to survive, Aspergillus fumigatus must adapt to specific niche environments. Adaptation to the human host includes modifications facilitating persistent colonisation and the development of azole resistance. The aim of this study is to advance understanding of the genetic and physiological adaptation of A. fumigatus in patients during infection and treatment. Thirteen A. fumigatus strains were isolated from a single chronic granulomatous disease patient suffering from persistent and recurrent invasive aspergillosis over a period of 2 years. All strains had identical microsatellite genotypes and were considered isogenic. Whole genome comparisons identified 248 non-synonymous single nucleotide polymorphisms. These non-synonymous mutations have potential to play a role in in-host adaptation. The first 2 strains isolated were azole susceptible, whereas later isolates were itraconazole, voriconazole and/or posaconazole resistant. Growth assays in the presence and absence of various antifungal stressors highlighted minor changes in growth rate and stress resistance, with exception of one isolate showing a significant growth defect. Poor conidiation was observed in later isolates. In certain drug resistant isolates conidiation was restored in the presence of itraconazole. Differences in virulence were observed as demonstrated in a Galleria mellonella infection model. We conclude that the microevolution of A. fumigatus in this patient has driven the emergence of both Cyp51A-independent and Cyp51A-dependent, azole resistance mechanisms, and additional phenotypes that are likely to have promoted fungal persistence.

Functional analysis of an APSES transcription factor (GlSwi6) involved in fungal growth, fruiting body development and ganoderic-acid biosynthesis in Ganoderma lucidum

The APSES transcription factors have been identified as key regulators of fungal development and other biological processes in fungi. In the present study, the function of Ganoderma lucidum GlSwi6, a homolog of Saccharomyces cerevisiae Swi6, was characterized. RNAi was used to examine the function of GlSwi6 in G. lucidum. Silencing GlSwi6 resulted in multiple developmental defects, including reduced fungal growth and increased hyphal branching, and the GlSwi6-silenced strains did not exhibit primordium or fruiting body formation. In addition, the H₂O₂ and ganoderic-acid (GA) levels of the GlSwi6-silenced strains decreased approximately 50% and 25%, respectively, compared with those of the WT strain. Furthermore, the addition of H₂O₂ led to the recovery of the GA levels of GlSwi6-silenced strains, implying that GlSwi6 might regulate GA biosynthesis by regulating the intracellular ROS levels. Taken together, these results indicate that GlSwi6 is involved in fungal growth, development and GA biosynthesis in G. lucidum.

On-line monitoring of Aspergillus niger GH1 growth in a bioprocess for the production of ellagic acid and ellagitannase by solid-state fermentation

The present work describes the monitoring of CO₂ production by Aspergillus niger GH1 in a bioprocess for the production of ellagitannase (EAH) and ellagic acid by solid state fermentation. Pomegranate ellagitannins, mainly punicalagin, were used as carbon source and EAH inducer. A second condition, using ellagitannins and maltose as growth promoting carbon source, was tested. The ellagic acid production was quantified and the EAH activity was assayed. The accumulated metabolites were identified by HPLC-ESI-MS/MS. Higher CO₂ production (7.79mg/grams of dry material) was reached in media supplemented with maltose. Short-time lag phase (7.79h) and exponential phase (10.42h) were obtained using only ellagitannins, despite its lower CO₂ production (3.79mg/grams of dry material). Without the use of maltose lower ellagic acid (11.85mg/L/h) and EAH (21.80U/L/h) productivities were reached. The use of maltose enhances the productivity of EA (33.18mg/L/h) and EAH (33.70U/L/h). Besides of punicalin and ellagic acid, two unknown compounds with mass weight of 702 and 290g/mol (ions 701 and 289m/z in negative mode, respectively) were identified and characterized by HPLC-ESI-MS/MS analysis.

Growth modeling to control (in vitro) Fusarium verticillioides and Rhizopus stolonifer with thymol and carvacrol

The aim of this study was to evaluate the antifungal activity (in vitro) of thymol and carvacrol alone or in mixtures against Fusarium verticillioides and Rhizopus stolonifer, and to obtain primary growth models. Minimal inhibitory concentration (MIC) was evaluated with fungal radial growth with thymol or carvacrol concentrations (0-1600mg/l). Mixtures were evaluated using concentrations below MIC values. Radial growth curves were described by the modified Gompertz equation. MIC values of carvacrol were 200mg/l for both fungi. Meanwhile, MIC values of thymol were between 500 and 400mg/l for F. verticillioides and R. stolonifer, respectively. A synergistic effect below MIC concentrations for carvacrol (100mg/l) and thymol (100-375mg/l) was observed. Significant differences (p<0.05) between the Gompertz parameters for the antimicrobial concentrations and their tested mixtures established an inverse relationship between antimicrobial concentration and mycelial development of both fungi. Modified Gompertz parameters can be useful to determine fungistatic concentrations.

Visualization of the structural changes in plywood and gypsum board during the growth of Chaetomium globosum and Stachybotrys chartarum

Fungal growth in indoor environments is associated with many negative health effects. Many studies focus on brown- and white-rot fungi and their effect on wood, but there is none that reveals the influence of soft-rot fungi, such as Stachybotrys spp. and Chaetomium spp., on the structure of building materials such as plywood and gypsum wallboard. This study focuses on using micro-computed tomography (microCT) to investigate changes of the structure of plywood and gypsum wallboard during fungal degradation by S. chartarum and C. globosum. Changes in the materials as a result of dampness and fungal growth were determined by measuring porosity and pore shape via microCT. The results show that the composition of the building material influenced the level of penetration by fungi as shown by scanning electron microscopy (SEM). Plywood appeared to be the most affected, with the penetration of moisture and fungi throughout the whole thickness of the sample. Conversely, fungi grew only on the top cardboard in the gypsum wallboard and they did not have significant influence on the gypsum wallboard structure. The majority of the observed changes in gypsum wallboard occurred due to moisture. This paper suggests that the mycelium distribution within building materials and the structural changes, caused by dampness and fungal growth, depend on the type of the material.

Bayesian model selection framework for identifying growth patterns in filamentous fungi

This paper describes a rigorous methodology for quantification of model errors in fungal growth models. This is essential to choose the model that best describes the data and guide modeling efforts. Mathematical modeling of growth of filamentous fungi is necessary in fungal biology for gaining systems level understanding on hyphal and colony behaviors in different environments. A critical challenge in the development of these mathematical models arises from the indeterminate nature of their colony architecture, which is a result of processing diverse intracellular signals induced in response to a heterogeneous set of physical and nutritional factors. There exists a practical gap in connecting fungal growth models with measurement data. Here, we address this gap by introducing the first unified computational framework based on Bayesian inference that can quantify individual model errors and rank the statistical models based on their descriptive power against data. We show that this Bayesian model comparison is just a natural formalization of Occam׳s razor. The application of this framework is discussed in comparing three models in the context of synthetic data generated from a known true fungal growth model. This framework of model comparison achieves a trade-off between data fitness and model complexity and the quantified model error not only helps in calibrating and comparing the models, but also in making better predictions and guiding model refinements.

Pyrosequencing investigation into the influence of Cu2+, Zn2+, Fe2+ and I- mixtures on fungal diversity and toxigenic fungal growth in a fermented liquid feed

A L9(34) orthogonal experiment was conducted to evaluate the influence of 9 mixtures which consisted of Cu2+, Zn2+, Fe2+ and I- ions at different ion concentrations on fungal diversity and toxigenic fungal growth in a Bacillus subtilis-fermented liquid feed (FLF) using pyrosequencing. The maximal Chao estimator and Shannon index were achieved in the FLF with a mixture of Cu2+ (200 mg/kg), Zn2+ (160 mg/kg), Fe2+ (150 mg/kg) and I- (2.4 mg/kg). The minimal relative abundance of Aspergillus was achieved when a mixture of Cu2+ (200 mg/kg), Zn2+, Fe2+ and I- was added to the FLF. Compared with Zn2+, Fe2+ and I-, Cu2+ was the most important ion in inhibiting Aspergillus growth. Adding Zn2+ (160 mg/kg), Cu2+, Fe2+ and I- to the FLF minimized the relative abundance of Fusarium. It was Zn2+ instead of Cu2+ played a critical role in suppressing the growth of Fusarium. The proper use of the mixture of Cu2+, Zn2+, Fe2+ and I- in FLF contributes to inhibit the growth of mycotoxin-producing fungi during storage. The new findings of this study help farmers properly use the mixture of Cu2+, Zn2+, Fe2+ and I- to inhibit the growth of mycotoxin-producing fungi in the production of high quality FLF and alleviate mycotoxins damages to animals and humans.

Effects of temperature, water activity and incubation time on fungal growth and aflatoxin B1 production by toxinogenic Aspergillus flavus isolates on sorghum seeds

Sorghum, which is consumed in Tunisia as human food, suffers from severe colonization by several toxigenic fungi and contamination by mycotoxins. The Tunisian climate is characterized by high temperature and humidity that stimulates mold proliferation and mycotoxin accumulation in foodstuffs. This study investigated the effects of temperature (15, 25 and 37°C), water activity (aw, between 0.85 and 0.99) and incubation time (7, 14, 21 and 28 d) on fungal growth and aflatoxin B1 (AFB1) production by three Aspergillus flavus isolates (8, 10 and 14) inoculated on sorghum grains. The Baranyi model was applied to identify the limits of growth and mycotoxin production. Maximum diameter growth rates were observed at 0.99 a(w) at 37°C for two of the isolates. The minimum aw needed for mycelial growth was 0.91 at 25 and 37°C. At 15°C, only isolate 8 grew at 0.99 a(w). Aflatoxin B1 accumulation could be avoided by storing sorghum at low water activity levels (≤0.91 a(w)). Aflatoxin production was not observed at 15°C. This is the first work on the effects of water activity and temperature on A. flavus growth and AFB1 production by A. flavus isolates on sorghum grains.

Nail changes in female pemphigus vulgaris patients on immunosuppressive therapy

Background

Pemphigus vulgaris (PV) patients receiving immunosuppressive therapy may develop nail alterations resulting from infection, skin disorder, or drug regimen.

Objective

This study aims to describe nail changes in PV female patients receiving immunosuppressive therapy and to report the frequency of associated fungal and bacterial growth in the patients’ nails.

Methods

Twenty-five female PV patients who had at least one acquired finger or toenail abnormality and had been administered at least one immunosuppressive drug were included in the study. Nail alterations were recorded. Nail scrapings were collected from abnormal nails for fungal and bacterial examination.

Results

Positive fungal and bacterial cultures were detected in 20 (80%) of patients’ nail samples. Five patients reported nail alterations coinciding with disease onset, whereas 13 reported nail changes after administration of immunosuppressive therapy.

Limitations

Lack of a control group (patients on similar immunosuppressive medications for conditions other than PV) which would have further supported the findings demonstrated in this observational study.

Conclusion

Nail abnormalities in severe PV patients are frequently associated with fungal and bacterial growth. Immunosuppressive therapy potentially initiates such changes.

What is already known on this topic?

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Pemphigus vulgaris (PV) patients receiving immunosuppressive therapy may develop nail alterations resulting from infection, skin disorder, or drug regimen.

What does this article add to our knowledge?

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The duration of disease in severe PV appears to dictate the longevity of nail changes in patients, and immunosuppressive therapy may initiate these nail changes either alone or as a result of opportunistic bacterial and/or fungal growth affecting the nail unit. Accordingly, prompt treatment of PV utilizing a multidisciplinary approach (combined or sequential therapy) would presumably decrease the incidence of nail affection in PV patients on immunosuppressive therapy.

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Limitations of the present work include lack of a control group (patients on similar immunosuppressive medications for conditions other than PV), which would have further supported the findings demonstrated in this observational study.

The use of real-time PCR to study Penicillium chrysogenum growth kinetics on solid food at different water activities

Fungal growth on solid foods can make them unfit for human consumption, but certain specialty foods require fungi to produce their characteristic properties. In either case, a reliable way of measuring biomass is needed to study how various factors (e.g. water activity) affect fungal growth rates on these substrates. Biochemical markers such as chitin, glucosamine or ergosterol have been used to estimate fungal growth, but they cannot distinguish between individual species in mixed culture. In this study, a real-time polymerase chain reaction (rt-PCR) protocol specific for a target fungal species was used to quantify its DNA while growing on solid food. The measured amount of DNA was then related to the biomass present using an experimentally determined DNA-to-biomass ratio. The highly sensitive rt-PCR biomass assay was found to have a wide range, able to quantify the target DNA within a six orders-of-magnitude difference. The method was used to monitor germination and growth of Penicillium chrysogenum spores on a model porous food (cooked wheat flour) at 25°C and different water activities of 0.973, 0.936, and 0.843. No growth was observed at 0.843, but lag, exponential and stationary phases were identified in the growth curves for the higher water activities. The calculated specific growth rates (μ) during the exponential phase were almost identical, at 0.075/h and 0.076/h for aw=0.973 and 0.936, respectively. The specificity of the method was demonstrated by measuring the biomass of P. chrysogenum while growing together with Aspergillus niger on solid media at aw=0.973.

Membrane-assisted culture of fungal mycelium on agar plates for RNA extraction and pharmacological analyses

Fungal mycelium grown in liquid culture is easy to harvest for RNA extraction and gene expression analyses, but liquid cultures often develop rather heterogeneously. In contrast, growth of fungal mycelium on agar plates is highly reproducible. However, this biological material cannot be harvested easily for downstream analyses. This article describes a PVDF (polyvinylidene difluoride) membrane-assisted agar plate culture method that enables the harvest of mycelium grown on agar plates. This culture method leads to a strongly reduced variation in gene expression between biological replicates and requires less growth space as compared with liquid cultures.

Regulation of vectorial supply of vesicles to the hyphal tip determines thigmotropism in Neurospora crassa

Thigmotropism is the ability of an organism to respond to a topographical stimulus by altering its axis of growth. The thigmotropic response of the model fungus Neurospora crassa was quantified using microfabricated glass slides with ridges of defined height. We show that the polarity machinery at the hyphal tip plays a role in the thigmotropic response of N. crassa. Deletion of N. crassa genes encoding the formin, BNI-1, and the Rho-GTPase, CDC-42, an activator of BNI-1 in yeast, CDC-24, its guanine nucleotide exchange factor (GEF), and BEM-1, a scaffold protein in the same pathway, were all shown to significantly decrease the thigmotropic response. In contrast, deletion of genes encoding the cell end-marker protein, TEA-1, and KIP-1, the kinesin responsible for the localisation of TEA-1, significantly increased the thigmotropic response. These results suggest a mechanism of thigmotropism involving vesicle delivery to the hyphal tip via the actin cytoskeleton and microtubules. Neurospora crassa thigmotropic response differed subtly from that of Candida albicans where the stretch-activated calcium channel, Mid1, has been linked with thigmotropic behaviour. The MID-1 deficient mutant of N. crassa (Δmid-1) and the effects of calcium depletion were examined here but no change in the thigmotropic response was observed. However, SPRAY, a putative calcium channel protein, was shown to be required for N. crassa thigmotropism. We propose that the thigmotropic response is a result of changes in the polarity machinery at the hyphal tip which are thought to be downstream effects of calcium signalling pathways triggered by mechanical stress at the tip.

Biological Characterization of Marssonina coronaria Associated with Apple Blotch Disease

Marssonina coronaria associated with apple blotch disease causes severe premature defoliation, and is widely distributed in Korea. Thirteen isolates were collected from orchards located in Gyeongbuk Province from 2005~2007. All isolates displayed over 99.6% and 99.2% sequence similarity to each other in internal transcribed spacer regions and partial sequences of 28S rDNA, respectively. The isolates were phylogenetically closely related to Chinese isolates. Selected isolates did not differ in their pathogenicity. The optimum conditions for fungal growth were 20℃ and pH 6 on peptone potato dextrose agar (PPDA). Peptone and mannose were the best nitrogen and carbon source, respectively. Fungal growth was better on PPDA than on common potato dextrose agar. This study provides valuable information for integrated disease management program and facilitates the routine culturing of M. coronaria.

Plant hormones promote growth in lichen-forming fungi

The effect of plant hormones on the growth of lichen-forming fungi (LFF) was evaluated. The use of 2,3,5-triiodobenzoic acid and indole-3-butyric acid resulted in a 99% and 57% increase in dry weight of the lichen-forming fungus Nephromopsis ornata. The results suggest that some plant hormones can be used as inducers or stimulators of LFF growth for large-scale culture.

Effect of Ribitol and Plant Hormones on Aposymbiotical Growth of the Lichen-forming Fungi of Ramalina farinacea and Ramalina fastigiata

This study was aimed at evaluating the growth promoting effect of symbiotic algal polyol (ribitol) and plant hormones on the lichen-forming fungi (LFF), Ramalina farinacea (CH050010 and 40403) and Ramalina fastigiata. The addition of ribitol to basal (malt-yeast extract) medium enhanced the relative growth rates of all three LFF. R. farinacea (CH050010), R. farinacea (40403) and R. fastigiata (H06127) showed 35.3%, 29.0% and 29.3% higher growth rates, respectively, compared to the control. IBA (indole-3-butyric acid) and TIBA (2,3,5-tridobenzoic acid) also increased growth rates of the LFF by 34 to 64% and 7 to 28%, respectively, compared to the control. The combination of ribitol with IBA or TIBA synergistically increased the growth of all LFF. For example, ribitol and IBA treatments increased growth rates of R. farinacea (CH050010), R. farinacea (40403) and R. fastigiata (H06127) by 79.4%, 40.3% and 72.8% in, respectively, compared to those grown on the basal medium. The stimulating effect of ribitol and IBA on the LFF growth induced vertical development of the fungal mass in culture. We suggest that lichen-forming fungal growth of Ramalina lichens can be stimulated aposymbiotically by supplementing polyols and plant hormones to the basal medium in the mass production of lichen secondary metabolites under large scale culture conditions.