exo-Xylanase X from Aeromonas punctata ME-1 was functionally expressed in Escherichia coli with a carboxy terminal His tag (6x) 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 beta-d-1-thiogalactopyranoside. Its optimal temperature and pH were 50 A degrees 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 mu g(-1) for hydrolysis of Remazol Brilliant Blue-xylan but also a considerable exo-glucanase activity (27.9 U mg(-1)) on P-nitrophenyl beta-d-cellobioside. It hydrolyzed xylan predominantly to xylobiose, xylotriose, xylotetraose, and xylose. An enzyme mixture of exo-xylanase and endo-xylanase (50 mu g 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 mu g ml(-1), indicating a synergistic action between the two xylanases favoring the hydrolysis of beechwood xylan to release more xylose.