Efficient biodegradation of feathers by a novel and stable metallo-keratinase production strain Stenotrophomonas sp. Yang-5 isolated from swan farming soil

Feather waste produced by livestock and poultry breeding industry is a kind of biomass resource with great application prospect. Current study aims to obtain a feather-degradation bacteria that could efficiently biodegrade feather waste and maintain environmental friendliness. By using the casein agar medium, a novel keratinase production strain Stenotrophomonas sp. Yang-5 was isolated and then identified by subsequent 16S rRNA sequence. Further keratinase production medium was optimized by single factor and orthogonal experiments. Also, crude keratinase was characterized. Consequently, the highest enzyme activity of 161.95 +/- 3.65 U/mL was obtained after 48 h of incubation with optimized conditions consisting of reaction temperature 32.5 degrees C, initial pH 7.5, 0 g/L CaCl2, 50 g/L fructose, and 15 g/L feather. Yang-5 keratinase demonstrated a broad temperature range of 25 degrees C - 95 degrees C and optimal catalytic efficiency at pH 9.0. The keratinase had a half-life of more than 120 min at 70 degrees C, indicating satisfactory thermal stability. Furthermore, 0.25 mol/L Mg2+, Mn2+, K+, and Ca2+ could enhance the enzyme activity to some extent and assigned as the metallo-class of keratinase, among of which Mn2+ resulted in the highest improvement by 2-fold activity enhancement. In addition, 5% (v/v) reducing agents including DMSO, DTT and 2-mercaptoethanol all reinforced the enzyme activity by 3-5 folds. To sum up, thermostable alkaline metallo-keratinase from Stenotrophomonas sp. Yang-5 exhibited favorable stability and could serve as a promising candidate for feather waste degradation as well as environmental protection and feed additive industry. Graphical Abst ract