LACTOSE UTILIZATION AND ENZYMES ENCODED BY MEGAPLASMIDS IN RHIZOBIUM-MELILOTI SU47 - IMPLICATIONS FOR POPULATION STUDIES

Cell extracts prepared from Agrobacterium tumefaciens GMI9023 derivatives carrying megaplasmids from Rhizobium meliloti strain SU47 were examined by non-denaturing polyacrylamide gel electrophoresis and subsequent specific enzyme staining. The results demonstrated that an unidentified or 'nothing' dehydrogenase is encoded by the nod-nif megaplasmid pRmSU47a, and a beta-galactosidase activity that is required for growth on lactose as sole carbon source is encoded by the exo-thi megaplasmid pRmeSU47b. These results are of particular importance regarding the choice of markers used in bacterial population genetic studies.