Classification of bacteria nodulating Lathyrus japonicus and Lathyrus pratensis in northern Quebec as strains of Rhizobium leguminosarum biovar viciae

Abstract

The diversity of two populations of rhizobia isolated from Lathyrus japonicus (30 strains) and Lathyrus pratensis (49 strains) growing in northern regions of Quebec, Canada, was determined on the basis of phenotypic characteristics, multilocus enzyme electrophoresis, DNA-DNA homology, and 16S ribosomal DNA sequencing. According to numerical analysis of phenotypic characteristics, strains were divided into four groups. Strains isolated from L. pratensis fell in groups I to III; the latter included reference strains of Rhizobium leguminosarum. All strains isolated from L. japonicus were included in group IV. All strains had nodulation characteristics similar to those of R. leguminosarum bv. viciae. Strains isolated from L. japonicus originating from an arctic region were usually able to grow at 5 degrees C and were more likely to be tolerant to copper (CuCl2.H2O, 100 micrograms/ml) and lead [Pb(CH3COO)2, 500 micrograms/ml] than strains isolated from L. pratensis from a boreal zone. However, both populations of Lathyrus strains were adapted to the cold in comparison to reference strains from temperate regions. Each population had similar genetic diversity (H = 0.45), determined by multilocus enzyme electrophoresis of the loci encoding eight enzymes, but the diversity obtained by analyzing all strains including the reference strains (H = 0.58) was higher. Representative strains of both populations showed high levels of DNA homology among themselves and with R. leguminosarum. Partial sequences of the 16S ribosomal RNA genes were similar to those reported for R. leguminosarum bv. viciae. We conclude that the strains isolated from L. japonicus and L. pratensis belong to R. leguminosarum bv. viciae but are distinguishable by growth at 5 degrees C, which is a characteristic related to their geographic origin.