A study of Rhizobium leguminosarum biovar trifolii populations from soil extracts using randomly amplified polymorphic DNA profiles

This study has shown that isolates of Rhizobium leguminosarum biovar trifolii can be grouped on the basis of their randomly amplified polymorphic DNA (RAPD) fragment patterns. Evidence is presented that these groups are not entirely arbitrary but are consistent with other genetic and phenotypic characteristics. RAPD analysis has been used to assess the efficiency of a dispersion and differential centrifugation procedure used to extract bacteria from soil. Whilst the major groups of Rhizobium isolates in soils were also found in the extracts, some of the others were missing. This is also reflected in the finding, made by measuring abundance of organisms, that as many Rhizobium isolates are left in the residue as appear in the supernatant; more dispersion steps, possibly with different dispersants, are needed to maximize extraction. The technique has also demonstrated that dispersing soil by simply shaking it in water not only underestimates the numbers of Rhizobium isolates present but also masks much of their diversity.