Biochemical Characterization and Application of Thermostable-Alkaline Keratinase From Bacillus halodurans SW-X to Valorize Chicken Feather Wastes

Abstract

The production, purification, and characterization of thermostable-alkaline keratinase from Bacillus halodurans SW-X (keratinase_SW-X), and its applicability towards the production of white chicken feather hydrolysate and bioplastic starch/keratin production were investigated. A maximal keratinase activity of 16.05 ± 0.25 U/mL was achieved by cultivation of B. halodurans SW-X in 5 L stirred tank bioreactor at 47 °C, 200 rpm, and 2 vvm for 48 h. Keratinase_SW-X was purified as a monomeric protein with the estimated MW of 25 kDa, 14.4-fold, and 20% recovery yield. The protein was classified as thermostable-alkaline keratinase due to its optimal pH (pH 10) and temperature (70 °C), pH stability (pH 9.0–11), thermostability (> 3 h at 50–60 °C), and it showed the highest specificity towards chicken feather keratin with Km of 0.45 mg/mL, and Vmax of 3.51 μmol/min/mg. Crude keratinase_SW-X biodegraded white chicken feathers into two types of low (10–20 kDa) and high (≥ 30 kDa) chicken feather (keratin) hydrolysates, with total recovery yields of 30%. The bioplastic starch/keratin was synthesized using cassava starch (70%, w/w), glycerol (30%, w/w), and keratin hydrolysate (0–0.30%, w/w). The optimal concentration of keratin hydrolysate was 0.10% (w/w), resulting in improved strength and elongation at break, with a good appearance of the bioplastic starch/keratin. Our study suggests that B. halodurans SW-X is a potential strain for thermostable-alkaline keratinase production. Moreover, from environmental perspectives, keratinases_SW-X is a promising candidate enzyme that valorizes low cost chicken feather waste to a high value added product, indicating a novel approach for feather waste treatment and utilization.