Economic production of eco-friendly dehairing keratinase and antioxidant feather hydrolyzate using Bacillus halotolerans

Feather is a high recalcitrance keratin-based biomass, and keratin-degrading microorganisms have been seen as beneficial tools for its biodegradation and production of valuable products with biomedical and industrial applications. In the current study, the isolated keratinolytic bacteria was identified on the base of its 16 S rDNA sequencing data as Bacillus halotolerans, and its efficiency in the hydrolysis of feather with the preservation of most of its amino acid constituent was estimated by high-performance liquid chromatography Pico-Tag (HPLC PICO-TAG) method. The produced hydrolysate possessed antioxidant activity of 2,2-Diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity of 52.3 ± 5.6 mmole TE/g without possessing any cytotoxicity to human normal skin fibroplast cell line BJ-1 estimated by MTT assay. Moreover, the isolated strain was capable for producing keratinase under submerged fermentation of feather that was optimized by combining single-variable-at-a-time optimization with the application of statistical designs (Plackett-Burman and Box-Behnken). The optimum keratinase activity was 140.83 U/mL that was enhanced by 3.2-fold of the estimated initial activity, and the purified enzyme possessed optimum activity at pH 9.5 and 70 °C with a half-life of 69.3 min. Finally, the applicability of the purified enzyme in the dehairing of bovine hide was examined in comparison to sodium sulfide (Na₂S) and lime (Ca(OH)₂) conventional method. The results estimated the efficiency of the examined bio-treatment process, it achieved complete dehairing after 2 h with a good skin quality as manifested by scanning electron microscope (SEM). In addition, a significant reduction of the pollution load parameters was estimated.