Protease production by the keratinolytic Bacillus sp. CL18 through feather bioprocessing

Bacillus sp. CL18 was investigated to propose a bioprocess for protease production using feathers as organic substrate. In feather broth (FB), containing feathers as sole organic substrate (1-100 g l^-1), maximal protease production was observed at 30 g l^-1 (FB30) after 6 days of cultivation, whereas increased feather concentrations negatively affected protease production and feather degradation. Protease production peaks were always observed earlier during cultivations than maximal feather degradation. In FB30, 80% of initial feathers mass were degraded after 7 days. Addition of glucose, sucrose, starch, yeast extract (2 g l^-1), CaCl₂, or MgCl₂ (10 mmol l^-1) to FB30 decreased protease production and feather degradation. FB30 supplementation with NH₄Cl (1 g l^-1) resulted in less apparent negative effects on protease production, whereas peptone (2 g l^-1) increased protease yields earlier during cultivations (3 days). Through a central composite design employed to investigate the effects of peptone and NH₄Cl (0.5-4.5 g l^-1) on protease production and feather degradation, FB30 supplementation with peptone and NH₄Cl (0.5-1.1 g l^-1) increased protease production within a shorter cultivation time (5 days) and hastened complete feather degradation (6 days). Feather bioconversion concurs with sustainable production of value-added products.