Studies on the utilization of lactose by Corynebacterium glutamicum, bearing the lactose operon of Escherichia coli.

The entire Escherichia coli lactose operon was inserted into an E. coli/Corynebacterium glutamicum shuttle vector and introduced into the gram-positive host organism C. glutamicum R 163. Recombinant C. glutamicum strains carrying the lac genes downstream of an efficient promoter displayed rapid growth with lactose as the sole source of carbon. Two prerequisites were necessary to obtain good growth of C. glutamicum R 163 on lactose: presence of the lacY gene in addition to lacZ and an appropriate promoter for efficient transcription in C. glutamicum. The galactose moiety of lactose was not utilized but accumulated in the culture broth. C. glutamicum strains carrying only the lacZ (beta-galactosidase) gene but not lacY (lactose permease) were not able to grow in lactose minimal medium.