Characterization of a spontaneously segregating Cf16-v1 lysogen of Xanthomonas campestris pv. citri

Filamentous phage Cf16 undergoes a unique neolysogenic infectious cycle in Xanthomonas campestris pv. citri and generates stable lysogens. In contrast, we have isolated a distinctive unstable lysogen, designated LW. This new lysogen segregated spontaneously into three nonparental types, each with a unique combination of colony morphology, phage-producing capacity, and phage genome content. In a given population of LW lysogens the segregation frequency of these types varied randomly with drastic fluctuations from experiment to experiment. Heat and UV treatment failed to increase the segregation frequency with a magnitude matching the sporadic intrinsic fluctuations. The characteristics of an LW lysogen were transmitted through the phage it released. Designated as Cf16-v1, this phage, which produced clear instead of turbid plaques as its progenitor Cf16, was exceedingly unstable in the host cell. Only 4% of the infected cells, rather than 95% as in the case of Cf16, retained the phage genome and completed the neolysogenization process. The prophage integration site on the host chromosome, however, appeared to be the same for both phages.