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

The genetic relationships among bacteria nodulating Phaseolus vulgaris in a soil of Granada, Spain, were investigated by multilocus enzyme electrophor esis, restriction fragment length polymorphism and partial sequencing of th e 16S rRNA genes and restriction fragment length polymorphisms of symbiotic genes. Multilocus enzyme electrophoresis analysis of 39 isolates determine d 11 different electrophoretic types, clustered into three main genetic gro ups. Genetic distances between groups were above 0.8. Five different 16S rR NA gene alleles were identified in this population, corresponding to previo usly described rhizobial species, Rhizobium etli, Rhizobium fredii, Rhizobi um gallicum, Rhizobium giardinii and Rhizobium leguminosarum. Using R. etli strain CFN42 nifH and nodB genes as hybridization probes, identical restri ction fragment length polymorphism profiles were found among isolates belon ging to four different 16S rRNA gene species, indicative of interspecific g ene transfer. Most of the bean-nodulating strains carried three copies of n ifH and strongly hybridized to the nodB gene of R. etli CFN42, suggesting t hat their symbiotic plasmid genes are organized similarly. Combined data fr om multilocus enzyme electrophoresis and 16S allele characterization indica te 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. (C) 1999 F ederation of European Microbiological Societies. Published by Elsevier Scie nce B.V. All rights reserved.