Morphology and general characteristics of lytic phages infective on strains of Bradyrhizobium japonicum.

Biological characteristics of three isolated phages (SR1, SR2, and SR3) lytic against three Bradyrhizobium japonicum strains were studied. These phages had no cross-infectivity among the host strains. Phage morphology indicates that they belonged to Siphoviridae (long noncontractile tail; SR1 and SR2) and Podoviridae (short tail; SR3) classes of bacteriophages. Lytic cycle of phages studied under identical conditions showed a distinct adsorption rate (67.3-99.1%), latent period (150-300 min), rise period (60-150 min), and burst size (110-200 pfu/cell). Stability in liquids and inactivation by osmotic shock, thermal, and ultraviolet irradiation were also distinct in this heterogeneous phage group. Influence of soil factors such as temperature, soil moisture, soil pH, and degree of phage adsorption to the soil on phage survival was determined. Major percent of free infective phages were obtained after desorption of phages from soil. Overall, temperature appeared to be the most important parameter affecting rhizobiophage survival in the soil.