Production and characterization of thermostable xylanase and pectinase from Streptomyces sp QG-11-3

Streptomyces sp. QG-17-3, which produces a cellulase-free thermostable xylanase (96 IU ml(-1)) and a pectinase (46 IU ml(-1)), was isolated on Horikoshi medium supplemented with 1% w/v wheat bran. Carbon sources that favored xylanase production were rice bran (82 IU ml(-1)) and birch-wood xylan (81 IU ml(-1)); pectinase production was also stimulated by pectin and cotton seed cake (34 IU ml(-1) each). The partially purified xylanase and pectinase were optimally active at 60 degrees C. Both enzymes were 100% stable at 50 degrees C for more than 24 h. The half-lives of xylanase and pectinase at 70, 75 and 80 degrees C were 90, 75 and 9 min, and 90, 53 and 7 min, respectively. The optimum pH values for xylanase and pectinase were 8.6 and 3.0, respectively, at 60 degrees C. Xylanase and pectinase were stable over a broad pi-i range between 5.4 and 9.4 and 2.0 to 9.0, respectively retaining more than 85% of their activity. Ca2+ stimulated the activity of both enzymes up to 7%, whereas Cd2+, Co2+ Cr3+, iodoacetic acid and iodoacetamide inhibited xylanase up to 35% and pectinase up to 63%; at 1 mM, Hg2+ inhibited both enzymes completely.