Phage-induced Alterations of Cell Disposition, Phage Adsorption and Sensitivity, and Virulence in Xanthomonas citri

Abstract

Temperate phage PXC7 was isolated from smooth strain XCJ18 and propagated on smooth strain XCJ19 of Xanthomonas citri. It produced small turbid plaques with irregular borders. It was inactivated when heated at 77°C for 10min, exposed to chloroform for 1min, or irradiated under ultraviolet light (National GL-15) at the distance of 40cm for 75 seconds.
When phage PXC7 lysogenized XCJ19, the genetic characteristics of this bacterium were modified by an alteration of colony types from smooth to dwarf. Reversion occurred in the lysogenic dwarf clones to produce smooth colonies. Some of these revertant clones were lysogenic and the others non-lysogenic, either resistant or sensitive to phage PXC7. Both lysogenic and resistant smooth revertants were incapable of adsorbing phage PXC7. The receptor sites for PXC7 were suggested to be same as to those for virulent phage CP₂. Such a modification, therefore, may provide a safeguard in both lysogenic and resistant smooth revertants preventing lysis by CP₂ infection. In connection with these modifications, both lysogenic and resistant smooth revertants grew some of their cells in the form of chains. All of these alterations had not been found with the sensitive smooth revertant. Both lysogenization and persistency with lysogeny or resistance were, therefore, concluded to be ressonsible for these alterations.
The lysogenic dwarf convertant, after developing from its smooth original strain XCJ19, continued to liberate phage PXC7 spontaneously at the frequency considerably higher than its lysogenic smooth revertant. The resistant smooth revertant did not liberate the phage. They did so even after haing entered their susceptible host. As a result, the lysogenic dwarf convertant did not grow sufficiently to developving canker lesions as the lysogenic, resistant, and sensitive smooth revertants and smooth original strain XCJ19. Moreover, the lysogenic dwarf convertant also reverted in the leaf tissue in some of its cells to produce smooth colonies, which consisted of either lysogenic or sensitive cells.