Insertion sequence (IS) hybridization supports classification of Rhizobium meliloti by phage typing


  • This paper is the result of collaborative work between Agriculture Canada scientists at the Plant Research Centre and the Ste Foy Research Station. Les Barran and Eden Bromfield carry out research on R. meliloti population ecology and competition for nodulation of the legume host. Roger Wheatcroft is interested in the role of IS sequences in Rhizobium and the detection of microorganisms in the environment. Serge Laberge studies the molecular genetics of rhizobia originating from the high Arctic.

Fax +1 613 992 7909. Plant Research Centre Contribution No. 1516, Ste Foy Research Station Contribution No. 471.


Sixty-one isolates of Rhizobium meliloti from two field sites which had been previously classified into 15 phage types on the basis of sensitivity to 16 typing phages, were subjected to insertion sequence (IS) hybridization using DNA probes for ISRm3 and ISRm5. Isolates from all but one phage type contained ISRm3 (apparent copy no. 1–11) and all isolates contained ISRm5 (apparent copy no. 3–11). The isolates were placed into 24 IS classes based on differences in their respective ISRm3 and ISRm5 hybridization profiles. At either field site, isolates representing different phage types possessed IS hybridization profiles that differed from each other, while those comprising a specific type had identical or closely related profiles. Isolates from one phage type were unusual since they did not react with any of the typing phages and were shown by IS hybridization to constitute a heterogeneous group. Evidence for spatial effects were provided by isolates from two of six types present at both sites which fell into separate IS classes on the basis of their site of origin. These data have ecological implications and suggest that for a particular site, phage typing may be employed for the rapid assessment of the genetic diversity among field isolates.