The endosymbiotic bacteria have a very small genome. Examine the genome of an en

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One very good example for bacterial endosymbiont is the Carsonella ruddii, endosymbiont of the psyllium, Pachypsylla Venusta. It is considered to be the most smallest bacterial endosymbiont consisting of a small genome size and was sequenced successfully. It's genome contains only 182 ORFs ( Open Reading Frame), less than 3% intergenic DNA and has a GC content of 16.5%.

Another example for obligately intracellular bacteria is Blochmannia Pennsylvanicus, an obligate endosymbiont of Camponotus pennsylvanicus, helps to trace evolutionary changes through bacterial - ant interaction. B.pennsylvanicus genome consists of 792 kb, 654 bp circular chromosome was sequenced. This is AT rich genome has a relatively low percentage of coding DNA of 76.7 %, Ribosomal binding sites ( RBS) for 479 of 610 ORFs, but only 42 has canonical AGGAG motif. It largely reflects differential gene loss. Gene loss in the B. pennsylvanicus lineage is approximately ~6.5 times slower with loss or inactivation of one ORF per 4.0-5.0 Myr.

Endosymbionts have revealed convergent patterns of genome evolution, including genome reduction and a trend toward AT richness, also covers challenge assumptions about evolution within host cells.

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