Differential Expression of Zymomonas mobilis Sucrase Genes (sacB and sacC) in Escherichia coli and Sucrase Mutants of Zymomonas mobilis

The sacB and sacC genes encoding levansucrase and extracellular sucrase respectively were independently subcloned in pBluescript (high copy number) and in Z. mobilis-E. coli shuttle vector, pZA22 (low copy number). The expression of these genes were compared under identical background of E. coli and Z. mobilis host. The level of sacB gene expression in E. coli was almost ten fold less than the expression of sacC gene, irrespective of the growth medium or the host strain. In Z. mobilis the expression of sacB and sacC genes was shown to be subject to carbon source dependent regulation. The transcript of sacB and sacC was three fold higher in cells grown on sucrose than in cells grown on glucose/fructose. Northern blot analysis revealed that the transcript levels of sacC was approximately 2-3 times higher than that of sacB. These results suggested that the expression of sacC gene was more pronounced than sacB.