Plasmids and stability of symbiotic properties of Rhizobium trifolii.
A conjugal plasmid which encodes both peak nodulation genes and nitrogenase genes, and which is labeled with the transposon Tn5, was transferred to a wild-type Rhizobium trifolii strain to examine the stability and expression of the host range and fixation (Fix+) phenotypes. Transconjugates were isolated which were shown to initially form nitrogen-fixing nodules (Nod+ Fix+) on both clovers and peas. These hybrid strains were then repeatedly passaged through either pea or clover nodules or onto a solid agar medium to determine whether these broadened-host-range characteristics were stably maintained. An instability was noted in the capacity of some of these hybrids to form nitrogen-fixing nodules on all of the host plants used. The broadened nodulation ability was, however, more readily maintained. In some cases, the changes in the Nod+ Fix+ phenotype could be attributed to demonstrable changes in the plasmid profile of the hybrid strains, whereas in other cases no demonstrable plasmid alterations could be detected.
D003227:Conjugation, Genetic; D007887:Fabaceae / Q000382:microbiology; D009586:Nitrogen Fixation; D010944:Plants / Q000382:microbiology*; D010946:Plants, Medicinal; D010957:Plasmids; D012231:Rhizobium / Q000235:genetics* / Q000502:physiology; D013559:Symbiosis