Distinctive Genome Reduction Rates Revealed by Genomic Analyses of Two Coxiella-Like Endosymbionts in Ticks.
Bottom Line: Genome reduction is a hallmark of symbiotic genomes, and the rate and patterns of gene loss associated with this process have been investigated in several different symbiotic systems.However, in long-term host-associated coevolving symbiont clades, the genome size differences between strains are normally quite small and hence patterns of large-scale genome reduction can only be inferred from distant relatives.The CRt genome is an extreme example of a symbiont genome caught in the act of genome reduction, and the comparison between CLEAA and CRt indicates that losses of particular genes early on in this process can potentially greatly influence the speed of this process.
Affiliation: Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.Show MeSH
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Mentions: The second locus in C. burnetii has not been associated with phase variation but contains several genes normally associated with O-antigen biosynthesis (fig. 4B). Although several of the genes as well as the gene order is conserved between C. burnetii and CRt at this locus, nine of the genes contained in this locus in C. burnetii are missing or pseudogenized in CRt and instead the CRt genome contains four nonorthologous genes and one pseudogene. Phylogenetic analysis of the four genes shows that all of them consistently group together with various members of the alpha- and beta-proteobacteria (fig. 5). Although it is not possible to pinpoint the exact evolutionary origin of these genes, the phylogenetic reconstructions together with a conserved gene order of the locus in the genome of the alpha-proteobacterium Holospora obtusa, a macronuclear symbiont of the ciliate Paramecium caudatum (figs. 4B and 5), suggest that this region might have been horizontally transferred between these distantly related bacteria, although not very recently.Fig. 5.—
Affiliation: Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.