Fungal Biotransformation Research Articles

In Vitro Activation of Paraoxonase 1 by Steroids: An Experimental, Molecular Docking, and Molecular Modelling Study

AbstractParaoxonase 1 (PON1) is an antioxidant enzyme that prevents lipid oxidation by hydrolysing lipid peroxides in the oxidised low‐density lipoprotein (LDL) structure, bound to high‐density lipoprotein (HDL) in serum, and exhibits esterase and lactonase activity. In this work, the hPON1 enzyme was purified from human serum using a hydrophobic gel with Sepharose 4B‐L‐tyrosine‐naphthylamine, and the affinity of some steroid derivatives previously isolated from fungal steroid biotransformations was examined on the pure hPON1 enzyme. The results indicate that all these derivaties activate the hPON1 enzyme to a different extent. Additionally, the binding potential of the most active five steroid derivatives to the PON1 enzyme to form a stable complex was explored through molecular docking and molecular dynamics (MD) simulation. The compounds with the highest potency in the enzymatic assay, S‐8 and S‐20, had the highest binding potential to the enzyme. The stability of the complexes formed by the two compounds was assessed and compared to the stability of the unbound enzyme structure. The enzyme‐compound complexes generally had similar stability to the unbound enzyme structure. Together with this, the MD simulation revealed that compound S‐8 would remain inside the enzyme's binding site during the simulation period, unlike compound S‐20. This situation varies according to the respective derivatives’ functional groups and hydrophobic characteristics.

Optimization of biotransformation processes of Camarosporium laburnicola to improve production yields of potent telomerase activators

BackgroundTelomerase activators are promising agents for the healthy aging process and the treatment/prevention of short telomere-related and age-related diseases. The discovery of new telomerase activators and later optimizing their activities through chemical and biological transformations are crucial for the pharmaceutical sector. In our previous studies, several potent telomerase activators were discovered via fungal biotransformation, which in turn necessitated optimization of their production. It is practical to improve the production processes by implementing the design of experiment (DoE) strategy, leading to increased yield and productivity. In this study, we focused on optimizing biotransformation conditions utilizing Camarosporium laburnicola, a recently discovered filamentous fungus, to afford the target telomerase activators (E-CG-01, E-AG-01, and E-AG-02).ResultsDoE approaches were used to optimize the microbial biotransformation processes of C. laburnicola. Nine parameters were screened by Plackett-Burman Design, and three significant parameters (biotransformation time, temperature, shaking speed) were optimized using Central Composite Design. After conducting validation experiments, we were able to further enhance the production yield of target metabolites through scale-up studies in shake flasks (55.3-fold for E-AG-01, 13-fold for E-AG-02, and 1.96-fold for E-CG-01).ConclusionFollowing a process optimization study using C. laburnicola, a significant increase was achieved in the production yields. Thus, the present study demonstrates a promising methodology to increase the production yield of potent telomerase activators. Furthermore, C. laburnicola is identified as a potential biocatalyst for further industrial utilization.

Synthesis, fungal biotransformation, and evaluation of the antimicrobial potential of chalcones with a chlorine atom

Chalcones are intermediate products in the biosynthesis of flavonoids, which possess a wide range of biological properties, including antimicrobial and anticancer activities. The introduction of a chlorine atom and the glucosyl moiety into their structure may increase their bioavailability, bioactivity, and pharmacological use. The combined chemical and biotechnological methods can be applied to obtain such compounds. Therefore, 2-chloro-2′-hydroxychalcone and 3-chloro-2′-hydroxychalcone were synthesized and biotransformed in cultures of two strains of filamentous fungi, i.e. Isaria fumosorosea KCH J2 and Beauveria bassiana KCH J1.5 to obtain their novel glycosylated derivatives. Pharmacokinetics, drug-likeness, and biological activity of them were predicted using cheminformatics tools. 2-Chloro-2′-hydroxychalcone, 3-chloro-2′-hydroxychalcone, their main glycosylation products, and 2′-hydrochychalcone were screened for antimicrobial activity against several microbial strains. The growth of Escherichia coli 10,536 was completely inhibited by chalcones with a chlorine atom and 3-chlorodihydrochalcone 2′-O-β-d-(4″-O-methyl)-glucopyranoside. The strain Pseudomonas aeruginosa DSM 939 was the most resistant to the action of the tested compounds. However, chalcone aglycones and glycosides with a chlorine atom almost completely inhibited the growth of bacteria Staphylococcus aureus DSM 799 and yeast Candida albicans DSM 1386. The tested compounds had different effects on lactic acid bacteria depending on the tested species. In general, chlorinated chalcones were more effective in the inhibition of the tested microbial strains than their unchlorinated counterparts and aglycones were a little more effective than their glycosides.

Biotransformation of hydrocortisone succinate with whole cell cultures of Monascus purpureus and Cunninghamella echinulata

Hydrocortisone succinate (1) is a synthetic anti-inflammatory drug and key intermediate in the synthesis of other steroidal drugs. This work is based on the fungal biotransformation of 1, using Monascus purpureus and Cunninghamella echinulata strains. Comopound 1 was transformed into four metabolites, identified as hydrocortisone (2), 11β-hydroxyandrost-4-en-3,17-dione (3), Δ1-cortienic acid (4), and hydrocortisone-17-succinate (5), obtained through side chain cleavage, hydrolysis, dehydrogenation, and oxidation reactions. These compounds have previously been synthesized either chemically or enzymatically from different precursors. Though this is not the first report on the biotransformation of 1, but it obviously is a first, where the biotransformed products of compound 1 have been characterized structurally with the help of modern spectroscopic techniques. It is noteworthy that these products have already shown biological potential, however a more thorough investigation of the anti-inflammatory properties of these metabolites would be of high value. These results not only emphasize upon the immense potential of biotransformation in catalysis of reactions, otherwise not-achievable chemically, but also holds promise for the development of novel anti-inflammatory compounds.

Biotransformation of Ginsenoside Rb1 to Ginsenoside Rd and 7 Rare Ginsenosides Using Irpex lacteus with HPLC-HRMS/MS Identification.

The biotransformation of ginsenosides using microorganisms represents a promising and ecofriendly approach for the production of rare ginsenosides. The present study reports on the biotransformation of ginsenoside Rb1 using the fungus Irpex lacteus, resulting in the production of ginsenoside Rd and seven rare ginsenosides with novel structures. Employing high-performance liquid chromatography coupled with high-resolution tandem mass spectrometry, the identities of the transformation products were rapidly determined. Two sets of isomers with molecular weights of 980.56 and 962.55 were discovered among the seven rare ginsenosides, which were generated through the isomerization of the olefin chain in the protopanaxadiol (PPD)-type ginsenoside skeleton. Each isomer exhibited characteristic fragment ions and neutral loss patterns in their tandem mass spectra, providing evidence of their unique structures. Time-course experiments demonstrated that the transformation reaction reached equilibrium after 14 days, with Rb1 initially generating Rd and compound 5, followed by the formation of other rare ginsenosides. The biotransformation process catalyzed by I. lacteus was found to involve not only the typical deglycosylation reaction at the C-20 position but also hydroxylation at the C-22 and C-23 positions, as well as hydrogenation, transfer, and cyclization of the double bond at the C-24(25) position. These enzymatic capabilities extend to the structural modification of other PPD-type ginsenosides such as Rc and Rd, revealing the potential of I. lacteus for the production of a wider range of rare ginsenosides. The transformation activities observed in I. lacteus are unprecedented among fungal biotransformations of ginsenosides. This study highlights the application of a medicinal fungi-based biotransformation strategy for the generation of rare ginsenosides with enhanced structural diversity, thereby expanding the variety of bioactive compounds derived from ginseng.

Characterization and removal mechanism of fluoroquinolone-bioremediation by fungus Cladosporium cladosporioides 11 isolated from aquacultural sediments.

Antibiotics have been widely detected in aquatic environments, and fungal biotransformation receives considerable attention for antibiotic bioremediation. Here, a fungus designated Cladosporium cladosporioides 11 (CC11) with effective capacity to biotransform fluoroquinolones was isolated from aquaculture pond sediments. Enrofloxacin (ENR), ciprofloxacin (CIP) and ofloxacin (OFL) were considerably abated by CC11, and the antibacterial activities of the fluoroquinolones reduced significantly after CC11 treatment. Transcriptome analysis showed the removal of ENR, CIP and OFL by CC11 is a process of enzymatic degradation and biosorption which consists well with ligninolytic enzyme activities and sorption experiments under the same conditions. Additionally, CC11 significantly removed ENR in zebrafish culture water and reduced the residue of ENR in zebrafish. All these results evidenced the potential of CC11 as a novel environmentally friendly process for the removal of fluoroquinolones from aqueous systems and reduce fluoroquinolone residues in aquatic organisms.

Biotransformation of essential oil composition of Zanthoxylum limonella by the fungus Pleopunctum pseudoellipsoideum provides the products with enhanced antimicrobial activities

Microbial biotransformation presents an alternative technology for enhancing more valuable bioproducts. This study utilized three fungi including Pleopunctum pseudoellipsoideum, Stagonosporopsis pini, and Thyrostroma jaczewskii to biotransform Zanthoxylum limonella essential oil composition. The essential oil composition of Z. limonella treated with these fungi was analyzed by gas chromatography-mass spectrometry. Z. limonella oil treated with the fungus T. jaczewskii gave cryptone, neoiso-verbanol, and dehydro-linalool as the major compounds. P. pseudoellipsoideum treatment resulted in the transformation of linalool, cryptone, and thymol, while treatment with the fungus S. pini yielded major transformed compounds such as citronellic acid, cis-limonene oxide, and eucarvone. Varied enzymes produced by each fungus led to diverse transformed volatile profiles. Principal Coordinate Analysis (PCoA) was employed to analyze the volatile profiles of the transformed essential oils, effectively highlighting the distinct nature of fungal biotransformation. Antibacterial activities of the essential oils obtained from all treatments were tested. The Z. limonella oil treated with P. pseudoellipsoideum exhibited the highest antibacterial activity, followed by S. pini and T. jaczewskii, in comparison to pure Z. limonella oil. The results suggest the potential biocatalytic properties of these fungi as tools for enhancing novel value-added bioactive compounds for food and pharmaceutical applications.

Biotransformation potential of the R-(+)-limonene by endophytic fungi strain associated with Amazonian fruit Malpighia emarginata DC

This study aims to offer an account of the biotransformation of limonene through the endophytic fungi strains associated with the Amazonian fruit Malpighia emarginata. The fungal biotransformation was executed in flasks containing the substrate R-(+)-limonene in a mineral medium, which was further incubated at 28 °C on a rotary shaker (120 rpm) for 120 h. Samples of each culture were taken every 24 hours, extracted with ethyl acetate, and analyzed using gas chromatography–mass spectrometry with the National Institute of Standards and Technology database. In this study with five endophytic fungi strains, only Penicillium sp. AF- LAB4 was considered a potential biocatalyst found in the screening due to its capacity to use the R-(+)-limonene as the single carbon and energy source in a mineral medium since they eventually accumulated interesting compound as limonene-1,2-diol (128.10 μL/L) after 48 to 120 h of reaction. This achievement is important and supports the development of the production of natural aromas and demonstrates the potential of using this endophytic fungus strain from the fruit M. emarginata, as a new biocatalyst.

Mechanistic Insights into the Biodegradation of Carbon Dots by Fungal Laccase.

While carbon dots (CDs) have the potential to support the agricultural revolution, it remains obscure about their environmental fate and bioavailability by plants. Fungal laccase-mediated biotransformation of carbon nanomaterials has received little attention despite its known capacity to eliminate recalcitrant contaminants. Herein, we presented the initial investigation into the transformation of CDs by fungal laccase. The degradation rates of CDs were determined to be first-order in both substrate and enzyme. Computational docking studies showed that CDs preferentially bonded to the pocket of laccase on the basal plane rather than the edge through hydrogen bonds and hydrophobic interactions. Electrospray ionization-Fourier transform-ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS) and other characterizations revealed that the phenolic/amino lignins and tannins portions in CDs are susceptible to laccase transformation, resulting in graphitic structure damage and smaller-sized fragments. By using the 13C stable isotope labeling technique, we quantified the uptake and translocation of 13C-CDs by mung bean plants. 13C-CDs (10 mg L-1) accumulated in the root, stem, and leaf were estimated to be 291, 239, and 152 μg g-1 at day 5. We also evidenced that laccase treatment alters the particle size and surface chemistry of CDs, which could facilitate the uptake of CDs by plants and reduce their nanotoxicity to plants.

A fungal CYP from Beauveria bassiana with promiscuous steroid hydroxylation capabilities

Hydroxylation of steroid core is critical to the synthesis of steroid drugs. Direct sp3 C–H hydroxylation is challenging through chemical catalysis, alternatively, fungal biotransformation offers a possible solution to this problem. However, mining and metabolic engineering of cytochrome P450 monooxygenases (CYPs) is usually regarded as a more eco-friendly and efficient strategy. Herein, we report the mining and identification of a new steroid CYP (CYP68BE1) from Beauveria bassiana by transcriptomics, heterologous expression, in vivo and in vitro functional characterization. The catalytic promiscuity of CYP68BE1 was explored, and CYP68BE1 showed promiscuously and catalytically versatile, which is qualified for monohydroxylation on C11α, C1α, C6β and dihydroxylation on C1β,11α and C6β,11α of six steroids, leading to the production of key steroid intermediates required in the industrial synthesis of some indispensable steroid drugs. Molecular dynamics simulations were performed, revealing the molecular basis of different binding orientations of CYP68BE1 with different substrates. The discovery of CYP68BE1 offers a promising biocatalyst for enriching the steroid structural and functional diversity, which also can be applied to biosynthesize valuable steroid drug intermediates.

Fungal Biotransformation of Hazardous Organic Compounds in Wood Waste.

A diverse spectrum of organisms, such as fungi, bacteria, and actinomycetes, can degrade and transform organic matter, including wood, into valuable nutrients. A sustainable economy has the goal of efficiently using waste as raw materials, and in this optic, it uses biological preparations more and more often, supporting the decomposition of lignocellulosic waste. With reference to wood wastes, which are produced in a substantial amount by the forest and wood industry, one of the possibilities to biodegrade such lignocellulosic material is the composting process. In particular, microbiological inoculum containing dedicated fungi can contribute to the biodegradation of wood waste, as well as the biotransformation of substances from the protection of wood, such as pentachlorophenol (PCP), lindane (hexachlorobenzene) and polycyclic aromatic hydrocarbons (PAHs). The purpose of this research was to produce a literature review in terms of the selection of decay fungi that could potentially be used in toxic biotransformation unions. The findings of the literature review highlighted how fungi such as Bjerkandera adusta, Phanerochaete chrysosporium, and Trametes versicolor might be ingredients of biological consortia that can be effectively applied in composting wood waste containing substances such as pentachlorophenol, lindane, and polycyclic aromatic hydrocarbons (PAHs).

Time-Resolved Examination of Fungal Selenium Redox Transformations.

Selenium (Se) is both a micronutrient required for most life and an element of environmental concern due to its toxicity at high concentrations, and both bioavailability and toxicity are largely influenced by the Se oxidation state. Environmentally relevant fungi have been shown to aerobically reduce Se(IV) and Se(VI), the generally more toxic and bioavailable Se forms. The goal of this study was to shed light on fungal Se(IV) reduction pathways and biotransformation products over time and fungal growth stages. Two Ascomycete fungi were grown with moderate (0.1 mM) and high (0.5 mM) Se(IV) concentrations in batch culture over 1 month. Fungal growth was measured throughout the experiments, and aqueous and biomass-associated Se was quantified and speciated using analytical geochemistry, transmission electron microscopy (TEM), and synchrotron-based X-ray absorption spectroscopy (XAS) approaches. The results show that Se transformation products were largely Se(0) nanoparticles, with a smaller proportion of volatile, methylated Se compounds and Se-containing amino acids. Interestingly, the relative proportions of these products were consistent throughout all fungal growth stages, and the products appeared stable over time even as growth and Se(IV) concentration declined. This time-series experiment showing different biotransformation products throughout the different growth phases suggests that multiple mechanisms are responsible for Se detoxification, but some of these mechanisms might be independent of Se presence and serve other cellular functions. Knowing and predicting fungal Se transformation products has important implications for environmental and biological health as well as for biotechnology applications such as bioremediation, nanobiosensors, and chemotherapeutic agents.

Evaluation of the biotransformation of R-(+)-limonene to aroma compounds by Pestalotiopsis versicolor LabMicrA-478 isolated of Euterpe oleracea Martius

Fungal biotransformation is a pertinent strategy to overcome difficulties and problems arising from chemical synthesis and direct extraction from nature. This biotechnological approach is a relevant strategy to obtain high-added-value aroma compounds under environmentally friendly conditions. In order to understand the effect of an amazon endophytic fungus on the monoterpene substrate, this research work aims to investigate the biotransformation using cells cultivated of Pestalotiopsis versicolor LabMicrA-478 with R-(+)-limonene as a sole carbon and energy source. The main products of the limonene biotransformation identified by gas chromatography-mass spectrometry (Thermo Scientific™) with the NIST database were limonene-1,2-diol (74,97%) and limonene-1,2-epoxide (1.94%) in 120 hours of reaction. Finally, this is the first report to characterize the bioconversion of R-(+)-limonene by P. versicolor LabMicrA-478, as a biocatalyst.

Fungal Biotransformation of Chlordiazepoxide and Evaluation of Type and Kinetics of Fungal Enzyme

To produce an active metabolite of Chlordiazepoxide by fungal biotransformation in an easy and economic way and also to develop microbial models for drug metabolism studies. Chlordiazepoxide is metabolized in the liver by CYP3A4 and forms major active metabolite N-desmethyl chlordiazepoxide. The focus of the study was to explore the ability of six distinct fungi to biotransform the drug Chlordiazepoxide to its metabolites. Induction, Inhibition and kinetic studies were also conducted to find out the type and capability of enzyme involved in fungal biotransformation. The screening studies were performed and fermentation protocol was designed with two controls (culture control and drug control) and one sample. Extract metabolite samples were reconstituted and analysed using HPLC. Induction, Inhibition studies were conducted similarly by maintaining its respective controls using CYP3A4 inducer (Carbamazepine) and inhibitor (Fluoxetine), further kinetic studies were performed to find Km and Vmax of fungal biotransformation of Chlordiazepoxide. Among six organisms Aspergillus ochreus has shown an extra peak at 6.9 min. in HPLC when compared with its controls indicated the formation of metabolite. The metabolite thus formed was identified, isolated and structure was confirmed by mass spectrometry and NMR spectroscopy as Nor-chlordiazepoxide. During inhibition and induction studies, it was found that quantity of the metabolite was increased with inducer and decreased with inhibitor. The Km and Vmax of fungal metabolism of Chlordiazepoxide was 1.928 µg/ml and 0.1802 µg/ml/hr respectively. Aspergillus ochreus has the ability to biotransform the Chlordiazepoxide to its active metabolite by CYP3A4 like enzyme and it followed Michaelis-Menten kinetics.

Neuroprotective metabolites via fungal biotransformation of a novel sapogenin, cyclocephagenol

Cyclocephagenol (1), a novel cycloartane-type sapogenin with tetrahydropyran unit, is only encountered in Astragalus species. This rare sapogenin has never been a topic of biological activity or modification studies. The objectives of this study were; (i) to perform microbial transformation studies on cyclocephagenol (1) using Astragalus endophyte, Alternaria eureka 1E1BL1, followed by isolation and structural characterization of the metabolites; (ii) to investigate neuroprotective activities of the metabolites; (iii) to understand structure–activity relationships towards neuroprotection. The microbial transformation of cyclocephagenol (1) using Alternaria eureka resulted in the production of twenty-one (2–22) previously undescribed metabolites. Oxidation, monooxygenation, dehydration, methyl migration, epoxidation, and ring expansion reactions were observed on the triterpenoid skeleton. Structures of the compounds were established by 1D-, 2D-NMR, and HR-MS analyses. The neuroprotective activities of metabolites and parent compound (1) were evaluated against H2O2-induced cell injury. The structure–activity relationship (SAR) was established, and the results revealed that 1 and several other metabolites had potent neuroprotective activity. Further studies revealed that selected compounds reduced the amount of ROS and preserved the integrity of the mitochondrial membrane. This is the first report of microbial transformation of cyclocephagenol (1).

Drimane Sesquiterpene Alcohols with Activity against Candida Yeast Obtained by Biotransformation with Cladosporium antarcticum.

Fungal biotransformation is an attractive synthetic strategy to produce highly specific compounds with chemical functionality in regions of the carbon skeleton that are not easily activated by conventional organic chemistry methods. In this work, Cladosporium antarcticum isolated from sediments of Glacier Collins in Antarctica was used to obtain novel drimane sesquiterpenoids alcohols with activity against Candida yeast from drimendiol and epidrimendiol. These compounds were produced by the high-yield reduction of polygodial and isotadeonal with NaBH4 in methanol. Cladosporium antarcticum produced two major products from drimendiol, identified as 9α-hydroxydrimendiol (1, 41.4 mg, 19.4% yield) and 3β-hydroxydrimendiol (2, 74.8 mg, 35% yield), whereas the biotransformation of epidrimendiol yielded only one product, 9β-hydroxyepidrimendiol (3, 86.6 mg, 41.6% yield). The products were purified by column chromatography and their structure elucidated by NMR and MS. The antifungal activity of compounds 1-3 was analyzed against Candida albicans, C. krusei and C. parapsilosis, showing that compound 2 has a MIC lower than 15 µg/mL against the three-pathogenic yeast. In silico studies suggest that a possible mechanism of action for the novel compounds is the inhibition of the enzyme lanosterol 14α-demethylase, affecting the ergosterol synthesis.

Fungal biotransformations of anticholinesterase norbelladine derivatives to obtain new products and mimic mammalian metabolism

Norbelladine is the natural precursor of all alkaloids of the Amaryllidaceae family. These compounds have been reported to exert interesting biological activities. Particularly, galantamine is currently used in the palliative treatment of Alzheimer’s disease for its cholinergic effect. The biotransformation of two norbelladine analogues exhibiting anticholinesterase activity was studied using 11 fungi belonging to Aspergillus , Rhizopus , Cunninghamella and Fusarium genera. The substrates were refractory to biotransformation by all fungi screened, except by A. clavatus . Based on GC-MS analyses, we demonstrated that its enzymes were able to catalyse the oxidative cleavage of the C-N bond of the secondary amine of 4’- O -methylnorbelladine. On the other hand, the hindered phenolic hydroxy group at the 3’ position of the brominated derivative was regioselectively methylated. The latter compound was chemically synthesised for better characterisation and the biological assays showed that this metabolite exerted a lower inhibition of BChE and lost the anti-AChE activity. The metabolic pathways involved here were useful to mimic phase I and II xenobiotic metabolism in mammals and thus predict the products that could be formed. A new source of biocatalytic tools to obtain new protoalkaloid derivatives was also discovered. • Norbelladine derivatives have shown promising anticholinesterase activities. • Fungal model is useful to predict phase I and II metabolism in mammals. • Norbelladine analogues remained untransformed with most of the fungi tested. • Two norbelladine analogues were metabolised by Aspergillus clavatus . • Biotransformation of the brominated derivative led to loss of anti-AChE activity.

Production of Taxifolin from Astilbin by Fungal Biotransformation

Taxifolin is known to have multiple biological functions. It has been widely used as a multifunctional food additive, and consequently, the global demand for taxifolin is increasing. The main method for taxifolin production is an extraction from larch wood, but the global resources of larch are limited. Astilbin, taxifolin-3-o-rhamnoside, is abundant in many plants and much more readily available, meaning taxifolin can be obtained by deglycosylation of astilbin. In this study, a fungal strain, Aspergillus fumigatus SQH4, was isolated from an enrichment culture of Smilax glabra rhizome to achieve the deglycosylation reaction. A culture of SQH4, adjusted to pH 6.5, with 5 g/L astilbin achieved a yield of taxifolin of 91.3% after biotransformation for 14 h at 35 °C. These findings offer an alternative method for the production of taxifolin.

Symbiotic Fungi of an Ambrosia Beetle Alter the Volatile Bouquet of Cork Oak Seedlings.

In Portugal, fungal symbionts of the ambrosia beetle Platypus cylindrus affect tree vigor of cork oak (Quercus suber) and are linked with the cork oak decline process. Fungal symbionts play crucial roles in the life history of bark and ambrosia beetles and recent work indicates complex interactions on the fungal and plant metabolic level. Colonized trees may respond with an array of currently unknown volatile metabolites being indicative of such interactions, acting as infochemicals with their environment. In this study, we examined volatile organic compounds (VOCs) of cork oak seedlings wound inoculated with strains of three fungal associates of P. cylindrus (Raffaelea montetyi, R. quercina, and Ceratocystiopsis sp. nov.) over a 45-day period by means of thermodesorption gas chromatography-mass spectrometry techniques. Fungal strains induced largely quantitative but species-specific changes among the 58 VOCs characterized. Overall, monoterpenes-the major volatiles of cork oak foliage-were significantly reduced, possibly a result of fungal biotransformation. Acetophenone, sulcatone, and nonanal-volatiles known for mediating ambrosia beetle behavior-increased in response to fungal inoculation. Qualitative VOC profiles of excised tissue of wood lesions (21 VOCs) and pure fungal cultures (60 VOCs) showed little overlap with seedling VOCs, indicating their plant-derived but fungal-induced origin. This chemoecological study expands on the limited knowledge of VOCs as infochemicals emitted from oak trees threatened by oak decline in relation to beetle-vectored ophiostomatoid fungi. It opens new avenues of research to clarify mutualistic or pathogenic aspects of these complex symbiotic interactions and develop new control strategies for P. cylindrus, including its mycobiota.

Fungal biorecovery of cerium as oxalate and carbonate biominerals

Cerium is the most sought-after rare earth element (REE) for application in high-tech electronic devices and versatile nanomaterials. In this research, biomass-free spent culture media of Aspergillus niger and Neurospora crassa containing precipitant ligands (oxalate, carbonate) were investigated for their potential application in biorecovery of Ce from solution. Precipitation occurred after Ce3+ was mixed with biomass-free spent culture media and >99% Ce was recovered from media of both organisms. SEM showed that biogenic crystals with distinctive morphologies were formed in the biomass-free spent medium of A. niger. Irregularly-shaped nanoparticles with varying sizes ranging from 0.5 to 2 μm and amorphous biominerals were formed after mixing the carbonate-laden N. crassa supernatant, resulting from ureolysis of supplied urea, with Ce3+. Both biominerals contained Ce as the sole metal, and X-ray diffraction (XRD) and thermogravimetric analyses identified the biominerals resulting from the biomass-free A. niger and N. crassa spent media as cerium oxalate decahydrate [Ce2(C2O4)3·10H2O] and cerium carbonate [Ce2(CO3)3·8H2O], respectively. Thermal decomposition experiments showed that the biogenic Ce oxalates and carbonates could be subsequently transformed into ceria (CeO2). FTIR confirmed that both amorphous and nanoscale Ce carbonates contained carbonate (CO32−) groups. FTIR-multivariate analysis could classify the biominerals into three groups according to different Ce concentrations and showed that Ce carbonate biominerals of higher purity were produced when precipitated at higher Ce3+ concentrations. This work provides new understanding of fungal biotransformations of soluble REE species and their biorecovery using biomass-free fungal culture systems and indicates the potential of using recovered REE as precursors for the biosynthesis of novel nanomaterials.