Keratinolytic enzyme-mediated biodegradation of recalcitrant poultry feathers waste by newly isolated Bacillus sp. NKSP-7 under submerged fermentation

摘要

Microbial and enzymatic degradation of keratin waste is more preferred over various conventional approaches which are costly and not environmentally suitable. Diverse niches are auspicious for the discovery of new microorganisms. To discover novel keratinolytic bacteria, 60 isolates from different poultry dumping sites were initially screened, and among these found a potent keratinolytic isolate (NKSP-7) that displayed higher feather-degrading ability. The selected isolate was identified as Bacillus sp. NKSP-7 based on 16S rDNA sequencing as well as physiochemical and morphological characteristics. The strain NKSP-7 showed complete hydrolysis of native chicken feathers (10 g/L) in nutrient medium after 24 h of incubation at 37 degrees C under agitation (150 rev/min) and produced thermostable extracellular keratinase. The crude enzyme displayed maximal keratinolytic activity (34.7 U/mL) in phosphate buffer of pH 7.0, and at 60 degrees C using keratin azure as a substrate. Keratinolytic enzyme showed stability at 20-65 degrees C for 4 h over the pH range of 5.5-8.0. No obvious inhibitory influence was perceived by cations, organic solvents, EDTA, and detergents. Whereas, enzyme activity was enhanced by adding beta-mercaptoethanol, Na+, Cd2+, and Mn2+. All these notable features of keratinase make it a promising candidate for various industrial applications especially for dehairing process in leather industry, bioconversion of poultry waste, and in detergents formulations.