CHARACTERIZATION OF THE XYLANASES FROM THE NEW ISOLATED THERMOPHILIC XYLAN-DEGRADING BACILLUS THERMOLEOVORANS STRAIN K-3D AND BACILLUS-FLAVOTHERMUS STRAIN LB3A

Three strictly aerobic strains (K-1, K-3d and K-4) were isolated from a hot-spring in Kobe, Japan, and a facultative anaerobic strain LB3A w as isolated from sediments collected from the alkaline Lake Bogoria, K enya. All strains were thermophilic and capable of growth on xylan. On the basis of morphological, physiological and phylogenetic studies th e new aerobic isolates resemble the thermophilic species Bacillus ther moleovorans while the facultative anaerobic isolate LB3A resembles the facultative anaerobic thermophilic species Bacillus flavothermus. Whe n grown on xylan as sole carbon source, all isolates produce thermoact ive xylanases. Xylanases from strains K-3d and LB3A are active al temp eratures between 40 and 90 degrees C and pH values between 5.0 and 9.0 . Applying SDS-PAGE the crude xylanase complex of isolate K-3d was sho wn to be composed of two active bands, with molecular masses of 40 and 69 kDa. The crude xylanase complex of isolate LB3A, on the other hand , is composed of at least four activity bands with molecular masses ra nging from 80 to 130 kDa. Due to the product pattern of xylan hydrolys is both enzymes are classified as endoxylanases. The xylanolytic enzym e system of isolate K-3d produces xylotriose, xylotetraose and larger xylooligosacharides, whereas the xylanases from isolate LB3A release x ylotetraose as the major product of hydrolysis.