ORIGINAL RESEARCH PAPER Biochemical characterization of a surfactant- stable keratinase purified from Proteus vulgaris EMB-14 grown on low-cost feather meal Michael O. Babalola . Adeyemi O. Ayodeji . Olufemi S. Bamidele . Joshua O. Ajele Received: 6 December 2019 / Accepted: 25 July 2020 Ó Springer Nature B.V. 2020 Abstract Objectives The bioaccumulation of keratinous wastes from poultry and dairy industries poses a danger of instability to the biosphere due to resistance to common proteolysis and as such, microbial- and enzyme-mediated biodegradation are discussed. Results In submerged fermentation medium, Pro- teus vulgaris EMB-14 utilized and efficiently degraded feather, fur and scales by secreting exoge- nous keratinase. The keratinase was purified 14-fold as a monomeric 49 kDa by DEAE-Sephadex A-50 anion exchange and Sephadex G-100 size-exclusion chro- matography. It exhibited optimum activity at pH 9.0 and 60 °C and was alkaline thermostable (pH 7.0–11.0), retaining 87% of initial activity after 1 h pre-incubation at 60 °C. The K m and V max of the keratinase with keratin azure were respectively 0.283 mg/mL and 0.241 U/mL/min. Activity of P. vulgaris keratinase was stimulated by Ca 2? , Mg 2? , Zn 2? , Na ? and maintained in the presence of some denaturing agents, except b-mercaptoethanol while Cu 2? and Pb 2? showed competitive and non-compet- itive inhibition with K i 6.5 mM and 17.5 mM, respectively. Conclusion This purified P. vulgaris keratinase could be surveyed for the biotechnological transfor- mation of bioorganic keratinous wastes into valuable products such as soluble peptides, cosmetics and biodegradable thermoplastics. Keywords Poultry waste  Feather  Valorization  Keratinase  Purification  Inhibition Introduction In the face of rising global human population especially in Africa, production and consumption of poultry meat is increasing with concomitant genera- tion of unwanted feather wastes amidst others (Jin et al. 2017). These solid wastes (feathers, nails, hairs, horns and hooves) contain keratin, a fibrous and recalcitrant structural protein (Jaouadi et al. 2010; Lange et al. 2016) resistant to common proteolytic enzymes routinely used industrially. In fact, chicken feathers making up 5 to 7% of the total weight of mature chickens (de Oliveira et al. 2016) contain up to 80 to 90% keratin on dry mass basis (Ghosh et al. 2008). Keratinous substances are degraded by some microorganisms in a process known as keratinolysis by expressing specific keratinolytic enzymes (kerati- nases), non-specific proteases and some other enzymes. Keratinases [E.C.3.4.21.11] are usually M. O. Babalola  A. O. Ayodeji (&)  O. S. Bamidele  J. O. Ajele Enzymology and Microbial Biotechnology Unit, Department of Biochemistry, The Federal University of Technology, P.M.B. 704, Akure, Nigeria e-mail: ade.oayodeji@gmail.com; aoayodeji@futa.edu.ng 123 Biotechnol Lett https://doi.org/10.1007/s10529-020-02976-0