|Van Berkum, Peter|
Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/1999
Publication Date: N/A
Interpretive Summary: False indigo, native to the United States, is cultivated in Asia for erosion control, as a green manure, and for amorphin, which is a toxic principle for aphids, cinch bugs, cucumber beetles, and a repellent against cattle flies. This legume benefits from a nitrogen-fixing symbiosis, but the bacteria have not been cultured or characterized. This publication describes the isolation and characterization of the rhizobia which infect false indigo when grown in China. Several different groups of bacteria were identified, and a new species Mesorhizobium amorphae was proposed for one of the groups. This information will be useful to scientists and to industry because these rhizobia are available for further study and for the production of inoculants.
Technical Abstract: Fifty-five Chinese isolates from nodules of Amorpha fruticosa were characterized and compared with the type strains for the species and genera of bacteria which form nitrogen-fixing symbioses with leguminous host plants. A polyphasic approach, which included restriction fragment length polymorphism (RFLP) of PCR-amplified 16S rRNA genes, multilocus enzyme electrophoresis (MLEE), DNA-DNA hybridization, 16S rRNA gene sequencing, electrophoretic plasmid profiles, cross nodulation, and a phenotypic study, was used in our comparative analysis. The isolates originated from several different sites in China and they varied in their phenotypic and genetic characteristics. The majority of the isolates had moderate to slow growth rates, produced acid, and harbored a 930 kb symbiotic plasmid (pSym). Five different RFLP patterns were identified among the 16S rRNA genes of all the isolates. Isolates grouped by PCR-RFLP of the 16S rRNA genes also were separated into groups by variation in MLEE profiles and by DNA-DNA hybridization. A representative isolate from each of these DNA homology groups had a separate position in a phylogenetic tree as determined from sequencing analysis of the 16S rRNA genes. A new species, Mesorhizobium amorphae, is proposed for the majority of the isolates, which belonged to a moderately slow to slow-growing, acid-producing group, based upon their distinct phylogenetic position, their unique electrophoretic type, their low DNA homology with reference strains representing the species within the genus Mesorhizobium, and their distinct phenotypic features. Strain ACCC19665 was chosen as the type strain for the species.