Keratinolytic Potential of A Newly Isolated Bacillus sp. Strain 46-2 for Chicken Feather Degradation and Antioxidant Production

Efficient microbial conversion of chicken-feather keratin into value-added products offers a sustainable approach to waste valorization. Bacillus sp. strain 46-2, isolated from a hot spring in Thailand, produced extracellular caseinolytic and keratinolytic enzymes capable of degrading keratinous and non-keratinous protein substrates. The crude enzyme preparation remained active over a broad pH range of 6.0–11.0 and exhibited maximal caseinolytic and keratinolytic activities at 50 °C. Certain metal ions, including Cu²⁺, Ni²⁺, and Zn²⁺, reduced one or both activities, while SDS, Tween 20, and Triton X-100 also caused varying degrees of inhibition. The addition of reducing agents enhanced feather degradation, with β-mercaptoethanol and Na₂SO₃ increasing chicken-feather mass loss to 73% and 47%, respectively, after 24 h. SDS–PAGE and zymographic analyses revealed multiple proteolytic and keratinolytic activity bands, while inhibition by PMSF and EDTA suggested contributions from serine proteases and metal-dependent proteases. Peptide-rich fractions obtained from the culture supernatant exhibited ABTS radical-scavenging activity, with IC₅₀ values of 506.25, 449.70, and 190.10 µg mL⁻¹ for the >10 kDa, 3–10 kDa, and <3 kDa fractions, respectively. Thin-layer chromatography detected spots corresponding to leucine, valine, glutamic acid, serine, and glycine in the hydrolysate. Overall, Bacillus sp. strain 46-2 is a promising source of alkaline-active and moderately thermostable proteolytic and keratinolytic enzymes for the bioconversion of keratin-rich waste into amino acids and antioxidant peptide-rich fractions with potential value for cosmetic and healthcare-related applications.