HIGH-LEVEL PRODUCTION OF A CELLULASE-FREE XYLANASE IN GLUCOSE-LIMITEDFED-BATCH CULTURES OF A THERMOPHILIC BACILLUS STRAIN

Bacillus sp. strain XE and its mutant derivative strain D3 produce a t hermostable xylanase which is suitable for enzymatic bleaching of kraf t pulp. Xylanase synthesis was shown to be induced by the soluble prod ucts of xylan hydrolysis (xylooligosaccharide) and equally, catabolica lly-repressed when these oligosaccharides accumulate in the medium. An optimal balance between these two antagonistic effects was obtained i n a carbon-limited, fed-batch culture with continuous xylooligosacchar ide feeding. To reduce substrate cost, the xylooligosaccharide could b e 90% substituted by glucose without reduction of the xylanase product ion rate. Xylanase production ceased when the activity reached approxi mately 380 U ml(-1) due to an amino acid shortage. A continuous supply of exogenous amino acids allowed the production to continue to more t han 1000 U ml(-1). (C) 1997 Elsevier Science B.V.