Comparative analysis of bacterial expression systems for keratinase production.

To explore a better expression system for the production of keratinase, the keratinase gene from Bacillus licheniformis BBE11-1 was expressed in Escherichia coli, Bacillus subtilis, and Pichia pastoris. The corresponding recombinant keratinases were named ker E, ker B, and ker P, respectively. All recombinant keratinases had an optimal pH at 10 although the pH stability of ker E and ker P was higher than that of ker E. The optimal temperature and thermostability of ker P were enhanced compared with those of ker E and ker B. The recombinant keratinases were inhibited by Mn2+ but experienced little influence from other metal ions. Furthermore, all recombinant keratinases could retain almost 80 % activity after treatment with 1 M hydrogen peroxide for 5 h. Under optimized conditions in a 3-L fermenter, the maximum keratinase activities obtained from recombinant B. subtilis and P. pastoris were 3,010 and 1,050 U/mL, respectively. This maximum keratinase activity from B. subtilis is the highest activity ever reported for any bacterial strain. These results indicate that B. subtilis is the ideal host for keratinase production, with potential applications in textile processing and feed supplements.