12-32: Purification and characterization of endoxylanases produced by Bacillus circulans D1 on maltose as carbon source

            Bacillus circulans D1, a thermophilic and alkalophilic bacterial strain isolated from decayed wood produces two extracellular cellulase-free xylanases. The enzymes were purified to homogenity using SP Sepharose and MonoQ chromatography. Xylanase A was most active at pH 5.5 and Xylanase B at pH 6.5. Both enzymes had an optimal temperature of 65^oC. Regarding to pH stability, xylanase A retained around 60% of its activity after 24h of incubation in the pH range from 3.5 to 10.5, while xylanase B was found to be more stable, maintaining approximately 80% of its activity in the same pH range. Xylanase A was stable at temperatures up to 55^oC. Xylanase B was less stable, retaining only 29% of activity after 1 hour of incubation at 60^oC. Xylanase A activity was enhanced by many composts and inhibited by Fe⁺, Hg⁺, Ag⁺ and EDTA. Almost all composts tested inhibited Xylanase B activity, and only Zn²⁺ and Mg²⁺ enhanced its acitvity. The enzymes are endoxylanases and main products of xylan hydrolysis are xylobiose and xylooligosaccharides. K_m and V_max values were 3.54 and 4.88 mg/mL and 7.0 and 36.56 mmol xylose min^-1 mg^-1, respecitvely for Xylanase A and B.