Optimization of feather degradation by a Bacillus thuringiensis isolate using response surface methodology and investigation of the feather protein hydrolysate structure.

Valorization of chicken feather is a long-sought approach for its sustainable disposal. Being protein rich, hydrolyzed chicken feather has a wide range of applications, not limited to formulation of microbiological culture media, animal feed and biofertilizers, but extends to synthesis of bioplastic films, cosmetics, and biomedicals. In this study, a potent keratinolytic isolate was recovered from soil and identified by 16S rRNA as Bacillus thuringiensis. Feather degradation by the isolate was optimized through response surface methodology. First, one-variable-at-a-time technique to assign the factors that affect feather degradation, then Box-Behnken central composite design model were employed. The model, involving 3 independent variables (initial pH, inoculum size, and concentration of supplementary glucose), was significant (R 2 = 0.9716). According to the model, complete feather degradation is obtained at an inoculum size of B. thuringiensis B4 equal to 1×10 10 CFU/ml, when FMB (Feather Meal Broth) is supplemented with 1.5% (w/v) glucose and pH adjusted to 8.5. Protein content of the lysate was 327.8±25 μg/ml, and no carbohydrates were detected. SEM/EDX analysis has shown that the hydrolysate consisted mainly of O, P, S, and Se in addition to carbon, while FTIR images assured the presence of carboxyl and amino groups characteristic of peptides and amino acids. A potent keratinolytic isolate, that hydrolyzed 78% of chicken feather in 4 days, was recovered from soil and was identified as Bacillus thuringiensis. A Box-Behnken central composite design model was generated to determine the optimum conditions for complete feather hydrolysis. SEM/EDX analysis of the hydrolysate has shown it consisted mainly of O, P, S, and Se in addition to carbon, while FTIR images assured the presence of groups characteristic of peptides and amino acids. This article is protected by copyright. All rights reserved.