Molecular cloning and expression of a dextranase gene from Arthrobacter in Streptococcus sanguis

The gene coding for a dextranase activity of Arthrobacter CB-8, named dex gene, was isolated and cloned into Escherichia coli and into Streptococcus sanguis. The gene library was screened by transparent halo formation around the colonies grown on agar medium containing blue dextran. DNA fragment consisting of about 3,200 base pairs was prepared for further cloning procedures. Dextranase activity was detected in the periplasmic space of E. coli clones, using pUC19, pVA 838 and their derivatives. Dex gene was also introduced into S. sanguis Challis using pVA 838, a plasmid that is able to replicate in both E. coli and S. sanguis. But the clones did not express the dex gene. For the expression of dex gene in S. sanguis, a new shuttle vector was constructed, which contained the promoter region of a glucosyltransferase gene from S. mutans as well as the terminator region of ribosomal RNA from E. coli. The plasmid was designated pMNK. Using pMNK as vector, dex gene was expressed in S. sanguis. Dextranase activity was detected in the cellular fraction of the clones.