Sensitivity of four phages to host bacterium Ralstonia solanacearum and analysis of their receptors

Objective  To investigate the lysis abilities of different phages mixtures against Ralstonia solanacearum, study their effects on the generation of phage-resistant strains, and clarify the receptors of four types of phages.

Method  Four types of phages, including P1556-1, P1556-2, P7-1 and P1521, were mixed in pairs. The sizes of plaques on R. solanacearum plates were determined. The resistance of R. solanacearum to phages was measured by co-culture of R. solanacearum and phages. Adsorption tests using phages, lipopolysaccharide (LPS) and membrane protein were conducted to determine the receptors of phages.

Result  Phage P1556-1 produced the largest plaque, indicating a strong lytic ability against R. solanacearum. The plaque sizes from the mixtures of two types of phages did not significantly differ from those of individual phages, while mixing two types of phages could slow down the generation of phage-resistant strains. Phage P1556-2 could be adsorbed by LPS of R. solanacearum, phage P1521 could be adsorbed by both LPS and membrane protein, while phage P1556-1 and P7-1 could be adsorbed by neither LPS nor membrane protein.

Conclusion  Mixing different phages can not improve the lysis ability against R. solanacearum, but can delay the generation of resistant host strain. The receptors of different phages are different.