Purification and characterization of thermoalkalophilic xylanase isolated from the Enterobacter sp. MTCC 5112

Thermoalkalophilic Enterobacter sp. MTCC 5112 was isolated from a sediment sample collected from the Mandovi estuary on the west coast of India. This culture produced extracellular xylanase. The xylanase enzyme was isolated by ammonium sulfate (80%) fractionation and purified to homogeneity using size exclusion and ion exchange chromatography. The molecular mass of the xylanase was ∼43 kDa. The optimal pH of the xylanase activity was 9, and at room temperature it showed 100% stability at pH 7, 8 and 9 for 3 h. The optimal temperature for the enzyme activity was 100 °C at pH 9.0. At 80 °C and pH 9, 90% of the enzyme activity was retained after 40 min. At 70 and 60 °C, the enzyme retained 64% and 85% of its activity after 18 h, respectively, while at 50 °C and pH 9 the enzyme remained stable for days. For xylan, the enzyme gave a Km value of 3.3 mg ml−1 and a Vmax value of 5000 μmol min−1 mg−1 when the reaction was carried out at 100 °C and pH 9. In the presence of metal ions such as Co2+, Zn2+, Fe2+, Cu2+, Mg2+ and Ca2+ the activity of the enzyme increased, whereas strong inhibition of enzyme activity was observed in the presence of Hg2+ and EDTA. To the best of our knowledge, this is the first report on the production of xylanase by this bacterium.