Expression of Aeromonas punctata ME-1 exo-Xylanase X in E. coli for Efficient Hydrolysis of Xylan to Xylose

Abstract

exo-Xylanase X from Aeromonas punctata ME-1 was functionally expressed in Escherichia coli with a carboxy terminal His tag (6×) and a molecular mass of 39.42 kDa, which is in agreement with the prediction from its amino acid composition. The recombinant exo-xylanase reached 186 mg l⁻¹ after induction by isopropyl β-d-1-thiogalactopyranoside. Its optimal temperature and pH were 50 °C and 6, respectively. The enzyme showed not only an exo-xylanase activity with K _m of 3.90 mg ml⁻¹ and V _max of 12.9 U μg⁻¹ for hydrolysis of Remazol Brilliant Blue-xylan but also a considerable exo-glucanase activity (27.9 U mg⁻¹) on P-nitrophenyl β-d-cellobioside. It hydrolyzed xylan predominantly to xylobiose, xylotriose, xylotetraose, and xylose. An enzyme mixture of exo-xylanase and endo-xylanase (50 μg ml⁻¹ each) yielded a larger amount (330 mg l⁻¹) of xylose from beechwood xylan than the controls (270 and 150 mg l⁻¹) using them alone at 100 μg ml⁻¹, indicating a synergistic action between the two xylanases favoring the hydrolysis of beechwood xylan to release more xylose.