-

Separation of plasmid genom from chromosomal genom among rhizobial bacteria containing megaplasmids is very difficult. It is possible to separate plasmid genom and study common plasmids among bacteria through making a gene library, and using hybridization technique. In this study 200 isolates of Rhizobium leguminosarum bv. viciae were isolated from different areas and characterized by their plasmid profile patterns. Different plasmid profiles were studied by plasmid probes which had been detected from gene library. The results of hybridization technique showed that strain 7131 and 7 isolates of Rhizobium leguminosarum bv. viciae isolated form sewage sludge contaminated area had common plasmid. Isolates from noncontaminated aera didn’t have any common plasmid. This indicates that making gene library is a good technique in these kinds of studies.