ISOLATION AND CHARACTERIZATION OF BACTERIOPHAGES SPECIFIC FOR RHIZOBIUM-LEGUMINOSARUM BIOVAR PHASEOLI

Two lytic phages, designated as H3V and R2V, specific for Rhizobium le guminosarum biovar phaseoli, were isolated and characterized. Phage H3 V was active against four indigenous isolates (HURR-3, HURR-21, HURR-3 5, and HURR-56) and two standard strains (RCR-3605 and USDA-2669) wher eas R2V was specific to one indigenous (Raj-2) and one standard (USDA- 2676) strain; there was no cross infectivity. Both phages had distinct morphology; phage H3V had an oblate polyhedral head (58 x 76 nm) and a flexible noncontractile tail (120 x 10 nm), while phage R2V had a he xagonal head (56 nm wide) and a very short tail (11 x 10 nm). The lyti c cycle of phage R2V requires Ca2+ ions (1 mM), which considerably red uce its latent period and burst size. Adsorption and one-step growth e xperiments of phages revealed that H3V had a slower adsorption rate (0 .56 x 10(-9) cm3/min), a longer latent period (255 min), and a higher burst size (240 plaque-forming units/cell) than R2V, which had an adso rption rate of 0.94 x 10(-9) cm3/min, a 210-min latent period, and a b urst size of 200 plaque-forming units/cell. Inactivation of these phag es by heat, osmotic shock, and uv irradiation showed that phage H3V wa s comparatively more sensitive than R2V. These phages were frequently detected in healthy nodules of French beans (Phaseolus vulgaris) at tw o different field locations and no correlation between phage titer and nodule size or colour was observed. Phage titer varied from 2.8 x 10( 2) to 1.2 x 10(6) plaque-forming units/nodule.