Keratinase production by Bacillus pumilus GHD in solid-state fermentation using sugar cane bagasse: optimisation of culture conditions using a Box-Behnken experimental design

Abstract

Keratinase [EC 3.4.21/24/99.11] production by Bacillus pumilus GHD was investigated by solid-state fermentation (SSF) using sugar cane bagasse as a substrate. The SSF conditions were optimised using the “one variable at a time” strategy. A Box-Behnken design was employed to investigate the effects of adding the most common mineral salts on improving enzyme production. Maximal enzyme activity and amino acid production [730 ± 4.9 U/g dry solid (ds) and 368 ± 4.2 mg/g ds, respectively] was achieved using a combination of salts in concentrations of 0.087, 0.120, 0.204 g /10 g ds for NaCl, ZnCl2 and MgSO4, respectively. Capsicum annuum seeds were planted and irrigated with the amino-acid-rich culture filtrate of B. pumilus GHD. Growth rate, number of leaves and pigments (chlorophyll a and carotenoids) increased significantly with a 20-day irrigation at dilutions of 1:5 and 1:10 (v/v). The results of scanning electron microscopy showed the complete degradation of nail and horn upon treatment with the crude enzyme.