ARS | Publication request: MESORHIZOBIUM AMORPHASE, A RHIZOBIAL SPECIES THAT NODULATES AMORPHA FRUTICOSA, IS NATIVE TO AMERICAN SOILS.

Submitted to: Archives Of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 11, 2002
Publication Date: N/A

Interpretive Summary: Amorpha fruticosa is a legume native to the Americas. Because it is a legume it benefits from biological nitrogen fixation through a symbiosis with soil bacteria referred to as rhizobia. In agriculture, the benefit is in the form of enhanced efficiency of crop production. Management of biological nitrogen fixation involves the inoculation of the appropriate bacterial cultures at the time of sowing. These bacterial cultures are available to the farmer as inoculants manufactured by industry. The problem is that many different bacteria are available, but very little is known about their dispersal throughout different geographic regions. Here we report that rhizobia of Amorpha fruticosa isolated from American soils belong to the same species as those from Chinese soils. Since the host is very specific for its rhizobia, we concluded that they had been exported to China with the seed of Amorpha fruticosa and had colonized Chinese soils. Our results will be useful to scientists who are interested in rhizobial distribution, taxonomy and strain identification.

Technical Abstract: Amorpha fruticosa was inoculated with rhizosphere soil from Iowa, USA, and 140 rhizobia isolated from root nodules were compared with Mesorhizobium amorphae originating from Chinese soils. PCR-RFLP patterns of the 16S rRNA gene were the same. Symbiotic plasmids wer ethe same size and had a single nifHgene. DNA:DNA hybridization values, DNA G+C content, and induced Nod factor patterns also were similar. We concluded that the four genotypes distinguished among 53 representative American isolates were M. amorphae. Since A. fruticosa is native to the Americas and is highly specific in its nodulation requirement, M. amorphae probably was transmitted to China.