Abstract
BACKGROUND: Bacteriophage Phi12 is a member of the Cystoviridae and is distinct from Phi6, the first member of that family. We have recently isolated a number of related phages and five showed high similarity to Phi12 in the amino acid sequences of several proteins. Bacteriophage Phi2954 is a member of this group. RESULTS: Phi2954 was isolated from radish leaves and was found to have a genome of three segments of double-stranded RNA (dsRNA), placing it in the Cystoviridae. The base sequences for many of the genes and for the segment termini were similar but not identical to those of bacteriophage Phi12. However, the host specificity was for the type IV pili of Pseudomonas syringae HB10Y rather than for the rough LPS to which Phi12 attaches. Reverse genetics techniques enabled the production of infectious phage from cDNA copies of the genome. Phage were constructed with one, two or three genomic segments. Phage were also produced with altered transcriptional regulation. Although the pac sequences of Phi2954 show no similarity to those of Phi12, segment M of Phi2954 could be acquired by Phi12 resulting in a change of host specificity. CONCLUSIONS: We have isolated a new member of the bacteriophage family Cystoviridae and find that although it shows similarity to other members of the family, it has unique properties that help to elucidate viral strategies for genomic packaging and gene expression.