Characterization of a novel soluble melanin secreted by Gliomastix polychroma

ABSTRACT Melanin is a heterogeneous, amorphous biopolymer widely distributed across biological systems, yet most canonical forms are intrinsically insoluble. Soluble melanins are rare and remain poorly characterized, with pyomelanin and peptidomelanin representing the best-described fungal examples. Here, we report the isolation and characterization of a distinct form of soluble melanin secreted by the filamentous ascomycete Gliomastix polychroma (NFCCI 6138). The polymer is phenolic, nitrogenous, and possesses a low amino acid content (∼ 4%). The polymer adopts particles with a median diameter of 75 nm (Q1=60, Q3=95), suggesting that a small particle size may contribute to the observed aqueous solubility via colloidal dispersion. Whole-genome sequence analysis identified genes associated with the L-DOPA, dihydroxynaphthalene (DHN), and homogentisic acid (HGA) pathways. Likewise, chemical inhibition of melanin synthesis using tropolone, tricyclazole, and NTBC resulted in reduced pigmentation, supporting the involvement of multiple melanin biosynthetic routes. Together, these findings identify a distinct variant of soluble melanin from G. polychroma that does not conform to existing soluble melanin classifications, representing a biochemically atypical variant of fungal melanin. Competing Interest Statement The authors have declared no competing interest.