Genomic Islands and Phages in Bartonella Species
The 350-kbp difference in size between B. henselae and B. quintana is almost exclusively due to the presence of large genomic islands in B. henselae along with a higher extent of genetic redundancy in this genome. The four largest islands are a 55-kbp prophage and three genomic islands of size 72kbp, 34kbp, and 9kbp respectively. Additionally, there are 68 smaller unique regions in B. henselae (not found in B. quintana), referred to here as islets (A.C. Frank and S.G.E Andersson, unpublished results). These are 3.1 kb long on average. As many as 17 of 44 tRNAs in the B. henselae genome are associated with an island or islet, highlighting their role as anchors for foreign DNA.
There appears to be a close relationship between the prophage and the islands. All islands carry genes or remnants of genes that are present on the prophage, and there is also a high degree of repetition within and between the islands. In total, 46% of the genes from these regions belong to a repeat family, and 73% of the repeat families have a member from the phage or one of the islands. In addition, many of the repeated genes in the prophage and the islands have paralogs in pseudogenes or truncated copies within the islands themselves or in the islets.
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