Production,characterization of acetyl esterase from a rumen bacteria strain RB3, and application potential of the strain in biodegradation of crop residues

Acetyl esterase was produced by a bacterial strain RB₃ at a level of 0.59 U mL⁻¹. The strain was isolated from beef cattle rumen fluid under anaerobic condition, and was identified as Escherichia coli. The peak activity of the enzyme appeared after 48 h of culturing under anaerobic condition. The optimal pH of the enzyme activity was 8.0, and the optimal temperature was 40 °C. The K_m and V_max values on p-nitrophenyl acetate were 0.84 mM and 0.13 mmol p-nitrophenol liberated min⁻¹ mg of protein⁻¹ respectively. The enzyme activity could be promoted by Zn²⁺, Ni²⁺, Fe²⁺, and K⁺, and inhibited by Cu²⁺, Fe³⁺, Mn²⁺, Mg²⁺, Ca²⁺, and Co²⁺. Biodegradation of rice stalk and maize stover by the strain RB3 and Pleurotus ostreatus was compared. The strain showed higher degradation rate for hemicellulose in the crop residues, while P. ostreatus showed higher degradation rate for cellulose. This indicated the potential industrial application of the strain RB3, particularly in utilizing renewable lignocellulose containing acetyl xylan for fermentation of products.