Host-specific regulation of symbiotic nitrogen fixation in Rhizobium leguminosarum biovar trifolii.

Strains of Rhizobium leguminosarum bv. trifolii (Rlt) able to form effective nodules on Trifolium ambiguum (Caucasian clover, CC) form ineffective nodules on Trifolium repens (white clover, WC), whereas strains that form effective nodules on WC usually do not nodulate CC. Here, we investigate the genetic basis of the host-specific nitrogen-fixation phenotype of CC rhizobia.

Comparative sequence analysis of the symbiosis island of Mesorhizobium loti strain R7A.

The Mesorhizobium loti strain R7A symbiosis island is a 502-kb chromosomally integrated element which transfers to nonsymbiotic mesorhizobia in the environment, converting them to Lotus symbionts. It integrates into a phenylalanine tRNA gene in a process mediated by a P4-type integrase encoded at the left end of the element. We have determined the nucleotide sequence of the island and compared its deduced genetic complement with that reported for the 611-kb putative symbiosis island of M.