Characterization of a New Filamentous Phage Cf from Xanthomonas citri

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Abstract
We have isolated a new filamentous phage from Xanthomonas citri, a pathogenic bacterium of citrus canker. This phage, designated as Cf, measures 10075 ± 985 × 10-1 nm in length and forms an unusually clear but tiny plaque on the host within 12 h p.i. Infection by Cf neither killed nor drastically prevented host cells from propagation. However, the rate of host cell division was severely retarded. This phage exhibited an exceedingly narrow host range and was unstable in conventional tris buffer and synthetic medium routinely used for the preparation of other filamentous phages. Based on nucleotide composition analysis (which also revealed that Cf contains an unusual nucleotide), thermal denaturation characteristics and the hydroxyapatite column elution pattern, the genome of Cf was shown to be single-stranded (ss) DNA. During phage multiplication in host cells single-stranded virus DNA, replicative form I and replicative form II were detected. As shown by acrylamide gel electrophoresis, the size and conformation of the virus, RFI and RFII DNA species, were the same as their counterparts of another filamentous phage Xf.