XYLANASE PRODUCTION BY THERMOPHILIC BACILLUS-LICHENIFORMIS A99 IN SOLID-STATE FERMENTATION

The production of extracellular thermostable cellulase-free xylanase ( EC 3.2.1.8) by Bacillus licheniformis A99 was studied in solid-state f ermentation (SSF). Wheat bran was Sound to be the best substrate [16.3 U g(-1) dry bacterial bran (DBB)] among a few easily available lignoc ellulosics rested. The production of xylanase reached a peak in 72 h ( 16.8 U g(-1) DBB). A high level of enzyme (17.1 U g(-1) DBB) was produ ced in wheat bran moistened with tap water at a substrate-to-moistenin g agent ratio of 1:2.5 (w/v). The optimum temperature for xylanase pro duction was 50 degrees C. An elevated water activity suited the enzyme production most. Maximum enzyme production was recorded ill an aerate d glass column reactor (19.13 U g(-1) DBB). Repression by glucose was not evident in SSF even at 6% while it was seen in submerged fermentat ion (SmF) at or beyond 2%. Cultivation in large enamel trays yielded a xylanase titer (15-17 U g(-1) DBB in 72 h) that was comparable to tha t in flasks. The enzyme production was 22-fold higher in SSF than that in SmF. This is the first report on xylanase production by a thermoph ilic bacterial strain in SSF. (C) 1997 by Elsevier Science Inc.