Human health depends strongly on adequate nutrition. Symbiotic fixation of atmospheric dinitrogen by legume rhizobia is the major source of nitrogen in the human diet, as well as the major factor limiting legume crop yield. This project aims to characterize the alterations entailed in differentiation of the alfalfa symbiont Rhizobium meliloti from free-lving bacteria, which do not fix nitrogen, to the nitrogen-fixing bacteroid form. Three interrelated studies will be carried out. (1) Fix genes, required for differentiation, will be identified by transposition mutagenesis with a Tn5-lac promoter probe, which will allow characterization of regulatory circuitry. (2) Changes in the outer and inner bacterial membranes will be characterized as a function of bacterioid differentiation. (3) The heat shock response, which depends on a specific RNA polymerase sigma subunit, will be characterized in R. meliloti, as a possible genetic approach to identification of their sigma subunits suspected to be involved in differentiation. These studies should begin to define the molecular changes required for differentiation of the bacteria to a form that can fix nitrogen. Such information will ultimately be necessary for genetic engineering of nitrogen fixation, with benefits to human health and agronomy.
| Sharma, S B; Signer, E R (1990) Temporal and spatial regulation of the symbiotic genes of Rhizobium meliloti in planta revealed by transposon Tn5-gusA. Genes Dev 4:344-56 |
| Bent, A F; Signer, E R (1990) Rhizobium meliloti suhR suppresses the phenotype of an Escherichia coli RNA polymerase sigma 32 mutant. J Bacteriol 172:3559-68 |
