Agrobacterium Tumefaciens Nitrogen Fixation System Expresses in Sinorhizobium meliloti (=Rhizobium meliloti)

Kanvinde and Sastry (Appl. and Environ. Microbiol. 56:2087-2092, 1990) had previously demonstrated that A. tumefaciens has all the physiological characters of a diazotroph. Genetic evidence indicates that the genes responsible for the reaction are located on the chromosome between his and trp but nearer to the former. Using this information two recombinant plasmids were isolated: (a) a stable R68.45-prime, pSRK9, bearing his+ Nif+ trp+ of A. tumefaciens and (b) pHN20, a recombinant cosmid (with a his+ Nif insert, about 30 kb) selected from a gene bank. Both these plasmids have been shown to be able to express clearly and facilitate nitrogen fixation in S. meliloti nif K- and to some extant in nif H- backgrounds; the plasmids acted synergistically with the wild type itself as was evidenced by increased nitrogen fixation and dry weight.