ALKALINE-ACTIVE XYLANASE PRODUCED BY AN ALKALIPHILIC BACILLUS SP ISOLATED FROM KRAFT PULP

A Bacillus sp (V1-4) was isolated from hardwood kraft pulp. It was cap able of growing in diluted kraft black liquor at pH 11.5 and produced 49 IU (mu mol xylose min(-1) ml(-1)) of xylanase when cultivated in al kaline medium at pH 9. Maximal enzyme activity was obtained by cultiva tion in a defined alkaline medium with 2% birchwood xylan and 1% corn steep liquor at pH 9, but high enzyme production was also obtained on wheat bran. The apparent pH optimum of the enzyme varied with the pH u sed for cultivation and the buffer system employed for enzyme assay. W ith cultivation at pH 10 and assays performed in glycine buffer, maxim al activity was observed at pH 8.5; with phosphate buffer, maximal act ivity was between pH 6 and 7. The xylanase temperature optimum (at pH 7.0) was 55 degrees C. In the absence of substrate, at pH 9.0, the enz yme was stable at 50 degrees C for at least 30 min. Elecrophoretic ana lysis of the crude preparation showed one predominant xylanase with an alkaline pI. Biobleaching studies showed that the enzyme would bright en both hardwood and softwood kraft pulp and release chromophores at p H 7 and 9. Because kraft pulps are alkaline, this enzyme could be used for prebleaching with minimal pH adjustment.