Isolation and biological characterization of virulent phage infecting Ralstonia solanacearum

To utilize phage therapy in tobacco bacterial wilt controlling, R. solanacearum strain TB15-15 was used as a host bacterium to screen a phage from tobacco soil. Phage titer, multiplicity of infection (MOI), one-step growth curve and phage sensitivity to temperature and pH were measured by a two-layer plating method. The results showed that a virulent phage infecting TB15-15 strain was isolated from soil of a long-term tobacco planting field and named as RS-PII-1. The MOI, phage latent period, burst phase and burst size of RS-PII-1 were 1, 10 min, 100 min, 1 411, respectively. The lytic activity and burst size of RS-PII-1 was the highest at 40℃. When temperature was higher than 40℃, the activity of RS-PII-1 decreased gradually until it was lost at 60℃. Phage had a certain tolerance to pH change, RS-PII-1 showed a good lytic activity in the pH range of 4-8. The lytic activity was reduced when pH < 4 or >8, and the phage completely lost lytic activity at pH>11. These results suggested that using RS-PII-1 in an alkaline solution was not suitable.