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Appl Environ Microbiol, May 1998, p. 1845-1851, Vol. 64, No. 5
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

New Bradyrhizobium japonicum Strains That Possess High Copy Numbers of the Repeated Sequence RSalpha

Kiwamu Minamisawa,1,* Tsuyoshi Isawa,1 Yoko Nakatsuka,2 and Norikazu Ichikawa1

Institute of Genetic Ecology, Tohoku University, Katahira, Aobaku, Sendai 980-8577,1 and School of Agriculture, Ibaraki University, Ami, Ibaraki 300-03,2 Japan

Received 21 July 1997/Accepted 20 February 1998

In a survey of DNA fingerprints of indigenous Bradyrhizobium japonicum with the species-specific repeated sequences RSalpha and RSbeta , 21 isolates from three field sites showed numerous RS-specific hybridization bands. The isolates were designated highly reiterated sequence-possessing (HRS) isolates, and their DNA hybridization profiles were easily distinguished from the normal patterns. Some HRS isolates from two field sites possessed extremely high numbers of RSalpha copies, ranging from 86 to 175 (average, 128), and showed shifts and duplications of nif- and hup-specific hybridization bands. The HRS isolates exhibited slower growth than normal isolates, although no difference in symbiotic properties was detected between the HRS and normal isolates. Nucleotide sequence analysis of 16S rRNA genes showed that HRS isolates were strains of B. japonicum. There was no difference in the spectra of serological and hydrogenase groupings of normal and HRS isolates. Some HRS isolates possessed a tandem repeat RSalpha dimer that is similar to the structure of (IS30)2, which was shown to cause a burst of transpositional rearrangements in Escherichia coli. The results suggest that HRS isolates are derived from normal isolates in individual fields by genome rearrangements that may be mediated by insertion sequences such as RSalpha .

* Corresponding author. Mailing address: Institute of Genetic Ecology, Tohoku University, Katahira, Aoba-ku, Sendai 980-77, Japan. Phone: 81-22-217-5684. Fax: 81-22-263-9845. E-mail: kiwamu{at}ige.tohoku.ac.jp.

Appl Environ Microbiol, May 1998, p. 1845-1851, Vol. 64, No. 5
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


This article has been cited by other articles:

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  • Isawa, T., Sameshima, R., Mitsui, H., Minamisawa, K. (1999). IS1631 Occurrence in Bradyrhizobium japonicum Highly Reiterated Sequence-Possessing Strains with High Copy Numbers of Repeated Sequences RSalpha and RSbeta. Appl. Environ. Microbiol. 65: 3493-3501 [Abstract] [Full Text]  


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