The B. henselae Prophage

The prophage is an evolutionary mosaic, flanked on one side by a gene coding for tRNA and on the other side by an integrase gene. Only a few of the phage genes have homologues in other a-proteobacteria; these include the integrase gene which has homologues in all sequenced close relatives, two blocks of genes with similarity to a putative prophage in Wolbachia pipientis [60, 61], and a gene coding for single-stranded DNA-binding protein. Although there are a number of unknown genes, most genes encoded by the prophage have an assigned phage-related function. For instance, there are 12 copies of a phage antirepressor and some phage-related proteins. Taken together, this suggests that the inserted prophage may be able to direct the synthesis of a functional phage particle.

Interestingly, phage-like particles have been detected in several Bartonella species including B.quintana, B. henselae, and B.bacilliformis [61-63]. The particles contained 14-kbp linear segments of double-stranded heterologous DNA, and it seems likely that the structural proteins of the phage particles should be encoded by the prophage. However, the reported presence of a 14-kbp fragment also in B. quintana [63] is surprising since B. quintana does not carry the prophage. It remains to be determined whether the phage particles and the 14-kbp fragment are related to the B. henselae prophage.

The presence of the integrase in other a-proteobacteria and the similarities to Wolbachia prophage genes suggest that the common ancestor of the modern a-proteobacteria was infected by a phage, or possibly that the phages infecting Bartonella and Wolbachia species have access to a common gene pool. Interestingly, Bartonella, Wolbachia, and Rickettsia have all been identified in French cat fleas by polymerase chain reaction (PCR) using species-specific primers [64]. Thus, the cat flea may be involved in the horizontal transmission of sequences from Rickettsia, Wolbachia, and Bartonella via phage infections.

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