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: Two loci putatively associated with O-antigen and LPS production have been identified in C. burnetii (fig. 4) (Seshadri et al. 2003). In the first locus, which is deleted in several phase II variants of C. burnetii, there is no similarity between the genes in CRt and C. burnetii (fig. 4A) even though several of the genes in CRt are also putatively associated with O-antigen biosynthesis and the flanking genes are homologous and conserved in order between the two genomes. As there are no orthologs in other Legionellales for the genes found at this locus in either of the two species (C. burnetii or CRt), it is not possible to determine whether either of them is ancestral, whether they were both independently gained by HGT, or whether the difference between them results from deletions in either or both of the two lineages. Additional database searches and phylogenetic reconstruction did not indicate any consistent and close relationships between the genes present at this locus in CRt and any particular taxon. Hence, it is not possible to draw any conclusion about the evolutionary scenario that generated these differences. Interestingly though, this locus is present within the large tandem duplication in CRt.Fig. 4.—
Affiliation: Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.