XANTHOMONAS-CAMPESTRIS PV CITRI INFECTED WITH FILAMENTOUS PHAGE CF1 - PLAQUE TURBIDITY, VIRAL-DNA INTEGRATION, AND IMMUNITY

Filamentous phage Cfl isolated from Xanthomonas campestris pv. citri normally forms turbid plaques, and contains the integration life cycle. Genomic maps of Cfl, however, are still poorly defined. We show the localization of the plaque turbidity (pt) gene and of the integration-required region in the Cfl phage genome. The involvement of pt gene in the regulation of Cfl phage DNA synthesis was identified by substituting alternate DNA fragments between wild type and clear-plaque forming mutants. The functionally required region for integration of Cflt were identified by analyzing the site-specific integration of plasmids containing different phage DNA fragments in the absence of any functional origin of replication. In the present study, a new phage mutant producing smaller plaques was obtained. This phage can infect Cfl lysogens, and hence was named Cfltv. Host cells infected by Cfltv can release large numbers of phage particles. Furthermore, the ability to integrate Cfltv DNA into the host chromosome is lost. Sequence data revealed that an alteration of one base pair occurred in the Cfltv genome.