At least five rhizobial species nodulate Phaseolus vulgaris in a Spanish soil

Abstract

The genetic relationships among bacteria nodulating Phaseolus vulgaris in a soil of Granada, Spain, were investigated by multilocus enzyme electrophoresis, restriction fragment length polymorphism and partial sequencing of the 16S rRNA genes and restriction fragment length polymorphisms of symbiotic genes. Multilocus enzyme electrophoresis analysis of 39 isolates determined 11 different electrophoretic types, clustered into three main genetic groups. Genetic distances between groups were above 0.8. Five different 16S rRNA gene alleles were identified in this population, corresponding to previously described rhizobial species, Rhizobium etli, Sinorhizobium fredii, Rhizobium gallicum, Rhizobium giardinii and Rhizobium leguminosarum. Using R. etli strain CFN42 nifH and nodB genes as hybridization probes, identical restriction fragment length polymorphism profiles were found among isolates belonging to four different 16S rRNA gene species, indicative of interspecific gene transfer. Most of the bean-nodulating strains carried three copies of nifH and strongly hybridized to the nodB gene of R. etli CFN42, suggesting that their symbiotic plasmid genes are organized similarly. Combined data from multilocus enzyme electrophoresis and 16S allele characterization indicate that more than five bacterial species compose this rhizobial population, as almost identical 16S rDNA alleles were identified in isolates belonging to deeply divergent multilocus enzyme electrophoresis lineages.