XYLANASE PRODUCTION BY ASPERGILLUS-AWAMORI - DEVELOPMENT OF A MEDIUM AND OPTIMIZATION OF THE FERMENTATION PARAMETERS FOR THE PRODUCTION OF EXTRACELLULAR XYLANASE AND BETA-XYLOSIDASE WHILE MAINTAINING LOW PROTEASE PRODUCTION

A growth medium was developed for maximal production in batch culture of extracellular xylanase and beta-xylosidase by Aspergillus awamori CMI 142717 and a mutant (AANTG 43) derived from the wild-types strain. The optimum pH for the production of xylanase and beta-xylosidase was 4.0. The best temperature for xylanase production was 30-degrees-C; 35-degrees-C was optimal for beta-xylosidase. Protease production was never completely suppressed under any of the conditions tested. However, protease titre was 3.5-fold less than the control in medium in which proteose peptone and yeast extract were omitted: the level of xylanase was not affected (8.6 U mL-1), but beta-xylosidase titre was increased 4.7-fold to 1.5 U mL-1. When corn steep liquor was used as the sole nitrogen source, xylanase and beta-xylosidase titres were further increased by 1.5- and 1.9-fold, respectively. Of the carbon sources investigated, ball-milled oat straw or oat spelt xylan produced the highest titres of xylanase and beta-xylosidase. None of the soluble carbon sources investigated produced the high titres of xylanase or beta-xylosidase induced by either oat straw or oat spelt xylan. The optimum concentration of ball-milled oat straw for xylanase and beta-xylosidase was 2% and the optimum spore inoculum was between 10(6) and 10(7) spores/mL-1 final concentration. The level of xylanase activity obtained in the culture filtrates of the mutant was a remarkable 820 U mL-1 when the reducing sugar released was measured by the dinitrosalicylic acid method. This enzyme titre would appear to be the highest reported so far. The xylanases system contained the correct balance of enzymes to effect extensive hydrolysis of oat spelt xylan. The protease titre was very low.