Microbial keratinases : enzymes with promising biotechnological 3 applications 4 5

doi: 10.17113/ftb.56.03.18.5658 review 1 2 Microbial keratinases: enzymes with promising biotechnological 3 applications 4 5 Beti Vidmar and Maša Vodovnik 6 Chair of Microbiology and Microbial Biotechnology, Department of Animal Science, 7 Biotechnical Faculty, University of Ljubljana, Groblje 3, 1230 Domžale, Slovenia 8 9 Received: Jan 3, 2018 10 Accepted: May 31, 2018 11 12 Summary 13 Keratin is a complex and structurally stable protein found in human and animal hard tissues, 14 such as feathers, wool, hair, hoof and nails. Some of these, like feathers and wool, represent 15 one of the main sources of protein-rich waste with significant potential to be transformed into 16 value-added products such as feed, fertilizers or bioenergy. A major limitation impeding 17 valorization of keratinous substrates is their recalcitrant structure and resistance to hydrolysis 18 by common proteases. However, these substrates can be efficiently degraded by specialized 19 keratinolytic enzymes produced by some microorganisms. Keratinases have already found a 20 way in pharmaceutical, textile and leather industries. However, their wider implementation in 21 other processes, such as cost-effective (pre)treatment of poultry waste, still requires 22 optimization of production and performance of the available enzymes. Here we present a 23 comprehensive review covering molecular properties and characteristics of keratinases, their 24 classification, traditional and novel approaches in discovery of novel enzymes, production, 25 characterization, improvement and biotechnological applications. 26 27