Biochemical characterization of three keratinolytic enzymes from Stenotrophomonas maltophilia BBE11-1 for biodegrading keratin wastes

•Gram-negative strain Stenotrophomonas maltophilia BBE11-1 was isolated for keratin degradation.•Three novel keratinolytic enzymes were purified and partially characterized.•Cooperative enzymes completely degraded feathers within 24 h.•Wool cuticle layers were remarkably wiped off without damage of internal fibres.•Addition of K3 protein with K1 and K2 showed obvious structure change of wool.

Keratin-degrading strain Stenotrophomonas maltophilia BBE11-1 was isolated from a poultry farm. According to zymogram analysis, there were at least two keratinolytic enzymes produced. After three steps of purification by different chromatographies, three keratinolytic enzymes were effectively separated. Partial characterizations of three enzymes showed that K1, K2 and K3 were 48 kDa, 36 kDa and 17 kDa respectively. Alkaline pHs 7–11 and temperatures 40–50 °C were optimal for three enzymes. K3 protein cooperated with other two enzymes greatly enhanced keratinolytic activity and markedly degraded feather within 24 h. Cooperative action of K1 and K2 remarkably wiped off cuticle layers of wool without damaging internal fibers, and the addition of K3 with K1 and K2 also showed obvious structure change of wool. Cooperative mechanism of keratinous degradation and potential applications of keratin-waste hydrolysis or dehairing in leather industry by three enzymes were discussed.