The Metallotolerance and Biosorption of As(V) and Cr(VI) by Black Fungi

Abstract

A collection of 34 melanized fungi isolated previously from anthropogenic contaminated sites were assessed for their tolerance to toxic concentrations of As(V) and Cr(VI) anions. Three strains of the species Cyphellophora olivacea, Rhinocladiella similis, and Exophiala mesophila (Chaetothyriales) were identified as hyper-metallotolerant, with estimated IC50 values that ranged from 11.2 to 16.9 g L−1 for As(V) and from 2.0 to 3.4 g L−1 for Cr(VI). E. mesophila and R. similis were selected for subsequent assays on their biosorption capacity and kinetics under different pH values (4.0 and 6.5) and types of biomass (active and dead cells and melanin extracts). The fungal biosorption of As(V) was relatively ineffective, but significant removal of Cr(VI) was observed from liquid cultures. The Langmuir model with second-order kinetics showed maximum sorption capacities of 39.81 mg Cr6+ g−1 for R. similis and 95.26 mg Cr6+ g−1 for E. mesophila on a dry matter basis, respectively, while the kinetic constant for these two fungi was 1.32 × 10−6 and 1.39 × 10−7 g (mg Cr6+ min)−1. Similar experiments with melanin extracts of E. mesophila showed maximum sorption capacities of 544.84 mg Cr6+ g−1 and a kinetic constant of 1.67 × 10−6 g (mg Cr6+ min)−1. These results were compared to bibliographic data, suggesting that metallotolerance in black fungi might be the result of an outer cell-wall barrier to reduce the diffusion of toxic metals into the cytoplasm, as well as the inner cell wall biosorption of leaked metals by melanin.

Characterization of melanin from Exophiala mesophila with the prospect of potential biotechnological applications

“…In a previous paper (Medina-Armijo et al, 2024), we verified the biosorption capacity and kinetics of hexavalent Chromium Cr (VI) by whole cells and melanin extracts from the metallotolerant black fungus Exophiala mesophila strain IRTA-M2-F10. The aim in this study is to gain a deeper understanding of the properties of melanin from black fungi, specifically regarding its electrochemical properties and the binding of metals.…”

“…The black fungus Exophiala mesophila strain IRTA-M2-F10 (culture collection at the Institute of Agrifood Research and Technology, Spain) isolated previously from biodeteriorated glued ceramics was selected the source of fungal melanin because of its tolerance to heavy metals and easy cultivation under laboratory conditions ( Medina-Armijo et al., 2024 ). Active cultures of this fungus were routinely maintained on potato dextrose agar (PDA; Condalab, Spain) incubated at 25°C in the darkness.…”

“…Fungal melanization occurs at the cell wall, but, in black fungi, melanin accumulates within membrane-bounded organelles (rounded/elongated shape up to 500 nm in diameter) referred to as melanosomes, analogous to those found in animal cells ( D’Alba and Shawkey, 2019 ). While melanin is not essential for fungal growth and development, it provides protection against a variety of stressors, including UV and ionizing radiation ( Dadachova et al., 2008 ), the presence of heavy metals ( Medina-Armijo et al., 2024 ), and toxic organic compounds ( Prenafeta-Boldú et al., 2019a ). Melanin also acts as an antioxidant, neutralizing reactive oxygen species (ROS) that are produced in some of the above-mentioned stress conditions ( Jacobson and Tinnell, 1993 ).…”

“…The use of black fungi has already been proposed for a variety of biotechnological applications, such as the biosorption of heavy metals ( Medina-Armijo et al., 2024 ) and volatile aromatic hydrocarbons ( Prenafeta-Boldú et al., 2019b ). Melanin seems to play a fundamental role in binding and metabolizing these toxic molecules, as well as the secondary reactive products that might result from their metabolism.…”

Once upon a Time, There Was a Piece of Wood: Present Knowledge and Future Perspectives in Fungal Deterioration of Wooden Cultural Heritage in Terrestrial Ecosystems and Diagnostic Tools

“…Species belonging to the genera Aureobasidium, Cladosporium, Exophiala, and Rhinocladiella were also found to cope with highly toxic wood preservatives such as creosote, a complex mixture of chemicals including polycyclic aromatic hydrocarbons (PAHs) and arsenic, and CCA (chromated copper arsenate) [280,[288][289][290][291]. This is not surprising since these BF were repeatedly found in hydrocarbon-contaminated areas and revealed tolerance to heavy metals [292]. Due to environmental issues these preservatives have been replaced by alternative copper-based compounds such as alkaline copper quat (ACQ) and copperazole (CA), quats such as didecyldimethylammonium chloride (DDAC), and the isothiazolone 4,5-dichloro-2-n-octyl-4-isothiazol-3-one (DCOIT), and IPBC (3-iodo-2-propynylbutylcarbamate) [293].…”