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

Abstract

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 three independent variables (initial pH, inoculum size, and concentration of supplementary glucose), was significant (R2 = 0.9716). According to the model, complete feather degradation is obtained at an inoculum size of B. thuringiensis B4 equal to 1 × 1010 CFU/ml, when 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.