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Abstract
Xylanase B from Paenibacillus barcinonensis was cloned in shuttle vectors for Escherichia coli and Bacillus subtilis, and expressed in Bacillus hosts. Several recombinant strains were constructed, among which B. subtilis MW15/pRBSPOX20 showed the highest production. This recombinant strain consists of a protease double mutant host containing P. barcinonensis xynB gene under the control of a phage SPO2 strong promoter. Maximum production was found when the strain was cultured in nutrient broth supplemented with xylans. Analysis of xylanase B location in B. subtilis MW15/pRBSPOX20 showed that the enzyme remained cell-associated in young cultures, consistent with its intracellular location in its original host, P. barcinonensis, and the lack of a signal peptide. However, when cultures reached the stationary phase, xylanase B was released to the external medium as a result of cell lysis. The amount of enzyme located in the supernatants of old cultures could account for 50% of total xylanase activity. Analysis by SDS–PAGE showed that xylanase B is an abundant protein found in the culture medium in late stationary phase cultures.