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Appl. Environ. Microbiol., Feb 1995, 507-512, Vol 61, No. 2
BD Eardly, FS Wang, TS Whittam and RK Selander
Evolutionary genetic relationships among 146 bean-nodulating Rhizobium
strains, including 94 field isolates from three localities in Colombia and
36 strains from Mexico, were examined by multilocus enzyme electrophoresis
and restriction fragment length polymorphism analysis of a PCR-amplified
260-bp segment of the 16S rRNA gene. Seventy-five electrophoretic types
(ETs), corresponding to multilocus enzyme genotypes, were identified,
including a genotypically diverse group of 18 ETs in Colombia that is
strongly differentiated from the ETs of R. etli, which occur in Mexico,
Colombia, and Brazil. Most strains of the distinctive Colombian ETs carried
the same 16S rRNA allele as did strains of R. etli, but, surprisingly, 17
isolates of two of these ETs had the allele that is characteristic of R.
leguminosarum, and strains of two other divergent groups of ETs were also
polymorphic for the two alleles. No fully satisfactory explanation for the
occurrence of the R. leguminosarum 16S rRNA allele in three distantly
related groups of strains is available, but horizontal transfer and
recombination of the gene, in whole or in part, would seem to be more
plausible than convergence in nucleotide sequence.
Copyright © 1995, American Society for Microbiology
Species limits in Rhizobium populations that nodulate the common bean (Phaseolus vulgaris)
Penn State Berks Campus, Reading 19610, USA.
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