Microbial production of eumelanin from a desert-derived Aspergillus terreus: statistical optimization, comprehensive characterization, and in silico insights into breast cancer-associated targets

Abstract

Naturally derived microbial products are increasingly explored as sustainable sources of bioactive compounds for targeted cancer applications. Among these, eumelanin is a nitrogen-containing polymeric pigment produced by various microorganisms, including fungi, and is distinguished by its unique physicochemical properties, biocompatibility, and free radical scavenging capacity. Nevertheless, eumelanin-producing fungi from extreme desert habitats remain poorly explored, particularly those isolated from the Wadi Allaqi Biosphere Reserve, and comprehensive studies integrating production optimization, structural characterization, and breast cancer-focused cytotoxic evaluation are still limited. In this work, melanin was isolated from a rhizosphere soil-derived fungal isolate obtained from the Wadi Allaqi Biosphere Reserve and identified as Aspergillus terreus AUMC15773 through morphological examination and molecular characterization with accession number OP941720. To the best of our knowledge, this is the first report describing a melanin-producing A. terreus isolated from the Wadi Allaqi Biosphere Reserve, followed by comprehensive optimization, structural characterization, and breast cancer-focused cytotoxic evaluation. Melanin extraction was achieved using acid precipitation, followed by statistical optimization of culture parameters employing Plackett–Burman design and response surface methodology. This approach led to a marked increase in melanin yield, reaching 102.9 mg/10 mL compared to the initial production of 20.19 mg/10 mL indicating a 5.1 fold increase. Chromatographic analysis using thin-layer chromatography indicated a single band (Rf = 0.7), suggesting purified melanin. Structural and chemical features were confirmed using UV–visible spectroscopy, FTIR, Raman spectroscopy, and NMR, identifying the compound as DOPA-type eumelanin. Elemental profiling further supported this classification, showing a nitrogen-rich composition with low sulfur content. DPPH free radical scavenging activity assay indicated that extracted eu-melanin had antioxidant activity similar to ascorbic acid. The cytotoxic activity of the extracted eumelanin was evaluated using MCF-7 breast cancer cells and normal WI-38 fibroblasts. The purified pigment reduced the viability of MCF-7 cells while exhibiting minimal cytotoxicity toward WI-38 cells, indicating favorable biocompatibility. In silico, molecular docking revealed a stronger interaction with estrogen receptor alpha (ERα) (binding energy − 8.0 kcal/mol) compared to breast cancer susceptibility protein BRCA1 (− 6.6 kcal/mol), providing supportive computational evidence that complements the in vitro findings involving ERα modulation. This study establishes a desert-derived A. terreus isolate as a promising microbial cell factory for eumelanin production through statistical optimization and comprehensive structural characterization. The combined experimental and computational findings support the potential of the produced eumelanin for future breast cancer-related investigations. Nevertheless, further mechanistic studies and in vivo validation are required before its therapeutic applicability can be established.