The 160-Kilobase Genome of the Bacterial Endosymbiont <i>Carsonella</i>

TLDR

Previous studies suggest the minimal cellular genome could be as small as 400 kb. The psyllid symbiont Carsonella ruddii has a 159,662‑bp circular chromosome with 16.5% GC, making it the smallest and most AT‑rich bacterial genome known, characterized by 97% coding density, overlapping genes, reduced gene length, retained translation and amino‑acid biosynthesis genes, but lacking many essential genes, implying an organelle‑like status.

Abstract

Previous studies have suggested that the minimal cellular genome could be as small as 400 kilobases. Here, we report the complete genome sequence of the psyllid symbiont Carsonella ruddii, which consists of a circular chromosome of 159,662 base pairs, averaging 16.5% GC content. It is by far the smallest and most AT-rich bacterial genome yet characterized. The genome has a high coding density (97%) with many overlapping genes and reduced gene length. Genes for translation and amino acid biosynthesis are relatively well represented, but numerous genes considered essential for life are missing, suggesting that Carsonella may have achieved organelle-like status.