“…However, a few extremely alkalophilic keratinases with optimum pH between 10 and 13 were previously reported (Friedrich and Antranikian, 1996;Letourneau et al, 1998;Mitsuiki et al, 2006;Jaouadi et al, 2008Jaouadi et al, , 2010Tatineni et al, 2008;Benkiar et al, 2013;Paul et al, 2014b;Gong et al, 2015;Tian et al, 2019). The optimum temperature reported for the activity of several microbial keratinases was between 37 and 65 • C (Hossain et al, 2007;Bach et al, 2011;Jaouadi et al, 2013;Wu et al, 2017;Hassan et al, 2020b), whereas thermophilic keratinolytic proteases already characterized function optimally between 70 and 100 • C (Nam et al, 2002;Jaouadi et al, 2010;Kuo et al, 2012;Benkiar et al, 2013;Paul et al, 2014b;Gong et al, 2015). Many keratinases, irrespective of the sources, have been found to be catalytically active and stable over a temperature and pH range of 20 to 100 • C, and 4 to 13, respectively (Jaouadi et al, 2008(Jaouadi et al, , 2010Paul et al, 2014b;Gong et al, 2015;Jin et al, 2019).…”