B. quintana Harbors Remnants of the B. henselae Islands

B.quintana contains 26 islets with a total size of 79 kbp [37]. Very few genes in B. quintana lack a gene or pseudogene homologue in B. henselae, and only two of them show similarity to other organisms. One of them is a homologue to yopP from Yersinia enterocolitica, which is located between a prophage lysozyme homologue and tRNA gene. YopP is encoded on a virulence plasmid [67] that codes for a secreted effector molecule causing apoptosis in macrophages [68, 69]. The other is a putative toxin/hemolysin secretion transporter, present in Sinorhizobium loti, that is located adjacent to tRNAGln. The location of these two genes next to tRNAs and the association with phage remnants strongly suggest that they were transferred horizontally to B. quintana. However, it is not known whether this happened before or after the divergence of B. henselae and B. quintana.

The breakpoints for rearrangements between B. henselae and B. quintana coincide with long repeated sequences that consist of both genes and noncoding sequences located at the genomic islands in B. henseale. About half of the B. quintana islets contain remnants of the prophage or the B. henselae islands, and many are located at the breakpoint positions, indicating that the islands were present in a common ancestor of the two species. Comparison with B. melitensis suggests that recombination at repeated sequences on the islands mediated excision of sequence fragments and rearrangements in B. quintana [37].

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