XYLAN-HYDROLYZING ENZYMES FROM THERMOPHILIC AND MESOPHILIC FUNGI

Screening of 40 mesophillic and 13 thermophilic fungi indicated that enzyme activities capable of degrading oat spelt xylan extensively were produced by only a few of the mesophillic species investigated. The relatively low degree of hydrolysis effected by the enzymes from thermophilic organisms could be explained, in part, by their lack of beta-xylosidase. Several strains of Aspergillus awamori and Aspergillus phoenicis were notable in producing high xylanase and beta-xylosidase and low protease activities. Of the fungi tested, 13 produced activities capable of removing O-acetyl, arabinosyl, 4-O-methylglucuronyl, feruloyl and coumaroyl substituents from the backbone of xylan polysaccharides as well as endo-1,4-beta-D-xylanase and beta-1,4-xylosidase. When the growth medium contained oat spelt xylan as carbon source, higher levels of xylanase, beta-xylosidase and acetyl xylan esterase were found than in cultures containing meadow fescue grass but the latter were richer in ferulic acid and coumaric acid esterases and 4-O-methylglucuronidase. No single organism or carbon source used was capable of producing high levels of all the debranching enzymes as well as high levels of enzymes capable of cleaving the glycosidic linkages of the xylan backbone. The best balance of enzymes was obtained in cultures of A. awamori IMI 142717 and NRRL 2276 and A. phoenicis IMI 214827. Either of these would be suitable for strain improvement studies.