Abstract
Endophytic fungi are promising sources of natural pigments for sustainable textile dyeing and functional biomaterials. In this study, a pigment-producing fungal strain (T8) isolated from healthy leaves of Rhodomyrtus tomentosa was identified as Arcopilus cupreus based on morphology and ITS rDNA sequencing (100% similarity). The strain produced a vivid extracellular red pigment during submerged fermentation, producing 1.47 g of crude extracellular extract per gram of fungal biomass. The pigment was highly water-soluble and exhibited a maximum absorption at 500 nm. It showed excellent thermal and photostability, while pH influenced color variation from red to violet and brown. LC-MS/MS analysis identified oosporein as the predominant secondary metabolite, consistently detected in both ionization modes at 6.2 min with the highest signal intensity, indicating its role as the primary pigment compound. The pigment demonstrated moderate antioxidant activity (IC₅₀ = 59.45 µg/mL) and low cytotoxicity toward human dermal fibroblasts (> 85% viability at 2 mg/mL). Cotton dyeing showed strong color uptake, enhanced by alum mordant, and pH-dependent color variation, with selective antibacterial activity against Staphylococcus aureus. These findings highlight A. cupreus T8 as a promising source of stable, multifunctional pigments for eco-friendly textile applications, although further safety evaluation is required.