[Cloning and expression of beta-glucosidase gene in Xanthomonas campestris XA5-5]

A beta-glucosidase gene from Xanthomonas campestris XA5-5 was cloned in Escherichia coli with the broad-host-range plasmid pRK404. The beta-glucosidase encoding plasmid designated pLZS1 contained a 1.1kb PstI DNA fragment deriving from XA5-5. The plasmid pLZS1 was transconjugated by filter mating into XA5-5 producing homologous clones XA5-5(pLZS1). Plasmid stability analysis revealed that pLZS1 was more stable in XA5-5 than in E. coli JM83. The level of beta-glucosidase expressed in XA5-5 (pLZS1) was much higher than in E. coli JM83 (pLZS1) using salicin as the substrate. From the results obtained, it seems that the gene product of this cloned DNA fragment has higher affinity to salicin substrate, and in some sense reduces the affinity between the enzyme and pNPG substrate in XA5-5.