From Isolation to Genomics: Characterization of Aspergillus uvarum HT4 as a Novel Producer of Extracellular Tannase

Abstract

Tannases (tannin acyl hydrolases, EC 3.1.1.20) are enzymes of industrial interest due to their ability to hydrolyze hydrolyzable tannins into bioactive compounds like gallic acid. In this study fungal strains capable of producing extracellular tannase were isolated and identified. From tannin-rich substrates, 24 fungal isolates were obtained, of which 17 showed tannase activity. Molecular identification based on calmodulin gene sequencing identified three species of tannase-producing black aspergilli: Aspergillus luchuensis, A. niger (formerly A. welwitschiae), and A. uvarum. The isolate A. uvarum HT4 exhibited the highest extracellular tannase activity (182 U/mL) and was selected for further study. Whole-genome sequencing of HT4 revealed 15 putative tannase genes, most sharing high identity with A. uvarum CBS 121591. Two divergent genes appeared to be acquired via horizontal gene transfer from Aspergillus brunneoviolaceus and Penicillium angulare. Proteomic analysis of the secretome confirmed the expression of two extracellular tannases. The enzyme showed optimal activity at pH 5.0–6.0 and 40–50 °C. Secretome analysis revealed hydrolytic enzymes typical of saprophytic fungi in lignocellulose-rich environments. Importantly, no biosynthetic gene clusters of major mycotoxins were detected, supporting the biosafety of HT4 for industrial applications.