Biochemical characterization of an extreme alkaline and surfactant-stable keratinase derived from a newly isolated actinomycete Streptomyces aureofaciens K13

Abstract

Keratinase has attracted increasing attention in the field of biocatalysis in recent years because of its critical role in keratin resource exploitation and keratin waste degradation. However, conventional studies focused on keratinases from bacterial and fungal strains, especially those of the Bacillus genus, keratinase resources from actinomycetes are far from being fully explored. In this study, a novel keratinase-producing strain was isolated with wool as the sole carbon and nitrogen source and identified as Streptomyces aureofaciens K13. The keratinase was purified to electrophoretic homogeneity with a molecular mass of 46 kDa. The purified enzyme exhibited optimum activity at 75 °C and pH of 12.0. It remained extremely stable at alkaline pH values between 6 and 12 and at a high reaction temperature of 65 °C. The keratinase displayed significant activity toward casein, keratin, BSA and wool. It could be activated in the presence of K⁺, Cu²⁺, Mn²⁺, Ca²⁺, Li⁺, and Sr²⁺. The keratinase was completely inhibited by PMSF and moderately inhibited by EDTA, indicating that this keratinase is a metallo-serine keratinase. This enzyme could remain stable and even be promoted in the presence of surfactants, including SDS, Tween, and Triton; especially, 1% of Tween 80 and Triton X-100 could substantially enhance the activity by 46% and 38%, respectively. These results indicated certain advantages over conventional keratinases. The keratinase can completely remove blood stains when combined with detergents. The improvement effect of S. aureofaciens K13 keratinase by various surfactants and the favourable washing performance might indicate its significant application potential in the detergent industry. There are rare reports on keratinase production from S. aureofaciens.