Effective bioconversion of feather-waste Keratin by Thermo-Surfactant Stable Alkaline Keratinase produced from Aspergillus sp. DHE7 with promising biotechnological application in detergent formulations

Abstract

Keratin-rich wastes are troublesome pollutants that their accumulation could lead to environmental problems. Microbial degradation of keratin wastes has emerged as an alternative bio-catalyst to steam-pressure cooking and alkali hydrolysis for the recycling of such residues to value-added products. The current work investigates the purification and biochemical characterisation of an extracellular keratinase from new Aspergillus sp. DHE7 using turkey feathers as substrate. The enzyme was purified 31-fold with a final yield of 37.5%. Purified keratinase is monomeric and its molecular mass was estimated to be 33 kDa as demonstrated on SDS-PAGE. The enzyme was active in wide range of pH (7.0–11) and temperature (37–70 °C) profiles with maximum activity at pH 8.5 and 60 °C. The activity was strongly suppressed by phenylmethylsulfonyl fluoride (93.4% inhibition) and moderately inhibited by EDTA (41.2% inhibition), suggesting that the current keratinase belongs to serine-metalloprotease. Bivalent cations, such as Ca2+, Zn2+, and Mn2+, enhanced enzyme activity by 165.7%, 176.3%, and 194.8%, respectively. The purified keratinase exhibited a wide proteolytic activity towards soluble and insoluble protein substrates displaying its greater activity toward casein, keratin, bovine serum albumin, and gelatin, followed by feathers, goat hair, and wool, and was substantially stable and compliant with surfactants and commercial laundry detergents. The Km, Vmax, Kcat and Kcat/Km values on keratin were 2.2 mg/mL, 2702.7 U/mL, 136.5 s−1 and 62.04 (s−1/mg mL−1), respectively. According to these characteristics, Aspergillus sp. DHE7 keratinase is suggested as a potential candidate for use in detergent formulations (as an additive) and in various biotechnological applications.