A bacteriophage typing system for Rhizobium meliloti

Abstract

Fifteen specific bacteriophages, each active on particular strains of Rhizobium meliloti, have been selected from those isolated by enrichment of local soils. Variables affecting phage–host interaction have been examined and standardized. The differential susceptibility of individual R. meliloti strains to each phage produces a distinctive pattern of response which allows the segregation of each strain into one of the 80 different groups identified to date. Discrimination between strains with this typing system is reproducible with no change in phage type following extended subculture or plant infection and reisolation of strains from root nodules of alfalfa. The large number of different strains recognized by the system should make it very useful in experimentally controlled tests of selected strains in the nodulation of alfalfa plants.