Catabolite repression of the xylanase gene (xynA) expression in Bacillus stearothermophilus No. 236 and B-subtilis

Catabolite repression of the Bacillus stearothermophilus No. 236 xynA gene, encoding an extracellular xylanase, was investigated in this work. Express ion of the xynA gene in the B. stearothermophilus strain was found to be su bject to glucose catabolite repression, and the level of repression was abo ut 50-fold when the relative amounts of xynA transcript synthesized on diff erent carbon sources were analyzed. The experiments with the B. subtilis MW 15 strains carrying plasmids containing the xynA::aprA fusion gene showed t hat the cloned xynA gene did not require any specific carbon source for its induction. Nevertheless, the expression of the cloned gene was repressed b y the presence of glucose. From the nucleotide sequence of the cloned xynA gene, we found two potential catabolite responsive elements (cre) within it s reading frame region (cre-l: nucleotides +160 to +173 and cre-2: +173 to +186). Furthermore, by using various deletion derivatives of the xynA::aprA fusion plasmid (pMGW23), we suggested that only the cre-2 element might pl ay a role in the glucose catabolite repression. Repression level of the xyn A gene expression in the recombinant B. subtilis strain was estimated to be about 3-fold by analysis of the amounts of xynA transcript.