Cloning and expression of a Streptococcus mutans glucosyltransferase gene in Bacillus subtilis

The gtfA gene of Streptococcus mutans GS-5, which encodes a 55-kDa glucosyltransferase has been isolated from a genetic library in an Escherichia coli-Bacillus subtilis shuttle vector, pMK3. The construction containing the gene enables E. coli JM83 and a sucrase-deficient mutant of B. subtilis to grow on sucrose as the sole carbohydrate source. The gene is expressed under its own control in both organisms. The level of biochemical activity detectable in B. subtilis carrying the clone is approx. 50% of that found in E. coli harboring the same construction. In Bacillus, the gene is expressed through exponential and stationary phases of growth with a decrease in activity as the culture enters stationary phase, corresponding to increases in intracellular protease levels. The enzyme produced in E. coli or B. subtilis harboring the cloned gene is identical to the enzyme produced by S. mutans GS-5 as determined by migration in native polyacrylamide gels.