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Appl. Environ. Microbiol., 08 1996, 2818-2825, Vol 62, No. 8
JT Sullivan, BD Eardly, P van Berkum and CW Ronson
Previously, we found that genetically diverse rhizobia nodulating Lotus
corniculatus at a field site devoid of naturalized rhizobia had symbiotic
DNA regions identical to those of ICMP3153, the inoculant strain used at
the site (J. T. Sullivan, H. N. Patrick, W. L. Lowther, D. B. Scott, and C.
W. Ronson, Proc. Natl. Acad. Sci. USA 92:8985-8989, 1995). In this study,
we characterized seven nonsymbiotic rhizobial isolates from the rhizosphere
of L. corniculatus. These included two from plants at the field site
sampled by Sullivan et al. and five from plants at a new field plot
adjacent to that site. The isolates did not nodulate Lotus species or
hybridize to symbiotic gene probes but did hybridize to genomic DNA probes
from Rhizobium loti. Their genetic relationships with symbiotic isolates
obtained from the same sites, with inoculant strain ICMP3153, and with R.
loti NZP2213T were determined by three methods. Genetic distance estimates
based on genomic DNA-DNA hybridization and multilocus enzyme
electrophoresis were correlated but were not consistently reflected by 16S
rRNA nucleotide sequence divergence. The nonsymbiotic isolates represented
four genomic species that were related to R. loti; the diverse symbiotic
isolates from the site belonged to one of these species. The inoculant
strain ICMP3153 belonged to a fifth genomic species that was more closely
related to Rhizobium huakuii. These results support the proposal that
nonsymbiotic rhizobia persist in soils in the absence of legumes and
acquire symbiotic genes from inoculant strains upon introduction of host
legumes.
Copyright © 1996, American Society for Microbiology
Four unnamed species of nonsymbiotic rhizobia isolated from the rhizosphere of Lotus corniculatus
Department of Microbiology, University of Otago, Dunedin, New Zealand.
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