Rhizobium population genetics: Enzyme polymorphism in isolates from peas, clover, beans and lucerne grown at the same site

Abstract

Isolates of Rhizobium meliloti and of R. leguminosarum biovars viceae, trifolii and phaseoli were obtained from a single site in Norfolk, England, and examined by enzyme electrophoresis of glucose-6-phosphate dehydrogenase, superoxide dismutase, β-galactosidase and esterases. All the enzymes had mobility variants, but the variation of the different enzymes was highly correlated, so that only a restricted number of combinations (electrophoretic types, ETs) were found. Some ETs were confined to a single biovar, but others were shared amongst R. leguminosarum biovars viceae, trifolii and phaseoli. Most R. meliloti isolates were quite distinct from those of R. leguminosarum. Electrophoresis of total soluble protein in the presence of sodium dodecyl sulphate revealed variation that correlated with the ET rather than with the host range. It is suggested that the Rhizobium isolates from this site comprise a number of genetically distinct lineages, some of which may carry any of several different host-range determinants, and which therefore appear in more than one biovar.