Keratinolytic proteases secreted by Bacillus subtilis obtained from feather-based submerged culture

Microbial keratin degradation has been recognized as a sustainable strategy for treating keratin-rich residues, as it avoids the use of environmentally harmful chemical agents. The present study aimed to evaluate the ability of Bacillus subtilis to degrade chicken feathers and to characterize the proteolytic enzymes it secretes. The enzymes were produced by B. subtilis in submerged fermentation, using chicken feathers (0.5% w/v) as the sole source of carbon and nitrogen. The resulting enzymatic extract contained multiple proteases, as evidenced by their detection in polyacrylamide gels copolymerized with gelatin. This extract exhibited distinct optimal pH ranges for keratinolytic and caseinolytic activities. Inhibition assays revealed that keratinolytic activity was strongly affected by phenylmethylsulfonyl fluoride (PMSF), with reductions of 49.3% at pH 7.0 and 88.4% at pH 9.5, and by ethylenediaminetetraacetic acid (EDTA), which caused inhibitions of 69.2% and 78.7% at pH 7.0 and 9.5, respectively. Caseinolytic activity was even more sensitive to these inhibitors, particularly at pH 9.5. Enzymes exhibiting higher activity at pH 7.0 displayed a greater capacity to hydrolyze native keratinous substrates compared with those active under alkaline conditions. Overall, these findings highlight B. subtilis as a promising source of keratinolytic enzymes with favorable biochemical properties for biotechnological applications, including biofilm dispersion and production of bioactive peptides.