Isolation, identification, optimization of enzyme-producing conditions and enzymatic activity of a feather-degradable Pseudomonas aeruginosa strain

Abstract:

[Objective] The aim of this study was to screen keratinase-producing strains from marine environment, investigate fermentation conditions and enzymatic properties, so as to provide strain resources and theoretical basis for the subsequent development and utilization of marine microbes to degrade feather waste.[Methods] The sludge from a marine duck farm in Beibu Gulf, Guangxi was used for bacterial isolation, and the strain with efficiently feather degradation ability was obtained by casein plate preliminary screening and keratinase activity re-screening. The strain was identified by morphology and molecular biology, and the enzyme-producing conditions were optimized by single-factor and orthogonal experiment. Finally, amino acid composition of feather degradation products and enzymatic properties were also studied.[Results] A strain of efficiently degrading feather was selected and identified as Pseudomonas aeruginosa Gxun-7. The optimum enzyme-producing conditions:feather 25 g/L, Zn²⁺ 0.10 g/L, initial pH 8.0, fermentation temperature 32.5℃, fermentation time 48 h, and the keratinase activity was 124.03 U/mL which was 2.3 times as high as before optimization. The analysis of enzyme properties showed that the optimum temperature was 70℃ and the optimum pH was 8.0. In the chemical reagent, mercaptoethanol could enhance enzymatic activity by 6.16 times, while phenylmethylsulfonyl fluoride (PMSF) decreased its relative activity to 15.00%. And it had excellent salt resistance (the relative activity in 20% NaCl retained 74.29%). There were 16 kinds of amino acids in the feather degradation products, including 7 kinds of essential amino acids. The total free amino acids content was as high as 2 329.80 mg/L, and the highest valine content was 575.89 mg/L.[Conclusion] P. aeruginosa Gxun-7 from marine environment had the ability to degrade feather keratin efficiently. The alkaline keratinase had excellent temperature and salt resistances, which had potential application value.