Nature Reviews Microbiology 10, 13-26 (January 2012) | doi:10.1038/nrmicro2670

Extreme genome reduction in symbiotic bacteria

John P. McCutcheon1 & Nancy A. Moran2  About the authors


Since 2006, numerous cases of bacterial symbionts with extraordinarily small genomes have been reported. These organisms represent independent lineages from diverse bacterial groups. They have diminutive gene sets that rival some mitochondria and chloroplasts in terms of gene numbers and lack genes that are considered to be essential in other bacteria. These symbionts have numerous features in common, such as extraordinarily fast protein evolution and a high abundance of chaperones. Together, these features point to highly degenerate genomes that retain only the most essential functions, often including a considerable fraction of genes that serve the hosts. These discoveries have implications for the concept of minimal genomes, the origins of cellular organelles, and studies of symbiosis and host-associated microbiota.

Author affiliations

  1. University of Montana, Division of Biological Sciences, 32 Campus Drive, HS104, Missoula, Montana 59812, USA.
  2. Yale University, Department of Ecology and Evolutionary Biology, 300 Heffernan Drive, West Haven, Connecticut 06516, USA.

Published online 8 November 2011