Characterization and prospective applications of melanin from black fungi in environmental biotechnology

Programa de Doctorat en Biotecnologia / Tesi realitzada a l'Institut de Recerca i Tecnologia Agroalimentàries (IRTA) [eng] Black fungi comprise a diverse group of ascomycetes characterized by their dark pigmentation due to the presence of melanin within their cells. This melanization process confers black fungi with a remarkable adaptability to a broad spectrum of harsh environments, including extreme temperatures, pH, water activity, and pressure values, as well as high levels of UV/ionizing radiation, and exposure to toxic chemicals. Over the past decade, fungal melanin has garnered increasing interest for its potential applications in organic semiconductors and bioelectronics, drug delivery systems, photoprotective materials, and environmental remediation processes. Despite significant advancements in these fields, the large-scale industrial application remains limited. Primarily due to the restricted availability and high cost associated with synthetic melanin production. Furthermore, the complex physicochemical properties of melanin, coupled with its low solubility in water and organic solvents, hamper both its study and practical utilization. This thesis investigated the metallotolerance of a collection of 34 strains of black fungi isolated from hydrocarbon-rich environments. Two metallotolerant strains belonging to Exophiala mesophila and Rhinocladiella similis were selected for subsequent biosorption experiments on As(V) and Cr(VI), as respective models of environmentally relevant metalloid and a heavy metal. The sorption efficacy of E. mesophila melanin extracts was studied in more detail and the sorption isotherm and kinetics were determined for Cr(VI). The results revealed high inter- and intraspecific variability in metallotolerance, suggesting the existence of additional physiological mechanisms beyond melanization that enable these fungi to cope with the toxic effects of metals and metalloids. A significant difference in the maximum Cr(VI) adsorption capacity (qmax) was observed between alive fungal biomass, dead biomass, and he fungal melanin extracts (alive biomass and extracted melanin, qmax: 95.26 vs. 544.84 mgCr6+ g⁻¹). A protocol for the production of E mesophila biomass and for the optimized extraction of melanin was developed to obtain sufficient yields of this biomaterial for subsequent fundamental and applied research. Fungal melanin was then characterized by using an array of spectrophotometric techniques (UV-Vis, FTIR, and EPR) an