• Open Access

Dynamics of genome evolution in facultative symbionts of aphids

Authors

  • Patrick H. Degnan,

    Corresponding author
    1. Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA.
    Search for more papers by this author
  • Teresa E. Leonardo,

    1. Howard Hughes Medical Institute and Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.
    Search for more papers by this author
    • Present address: US Agency for International Development, Bureau of Economic Growth, Agriculture, and Trade, Office of Environment and Science Policy, Washington DC 20523, USA. This whole Genome Shotgun project has been deposited at DDBJ/EMBL/GenBank under the accession ACYF00000000. The version described in this paper is the first version, ACYF01000000.

  • Bodil N. Cass,

    1. Center for Insect Science, University of Arizona, Tucson, AZ 85721, USA.
    Search for more papers by this author
  • Bonnie Hurwitz,

    1. Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA.
    Search for more papers by this author
  • David Stern,

    1. Howard Hughes Medical Institute and Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.
    Search for more papers by this author
  • Richard A. Gibbs,

    1. Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX 77030, USA.
    Search for more papers by this author
  • Stephen Richards,

    1. Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX 77030, USA.
    Search for more papers by this author
  • Nancy A. Moran

    1. Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA.
    Search for more papers by this author

E-mail pdegnan@email:.arizona.edu; Tel. (+1) 520 626 8344; Fax (+1) 520 621 9190.

Summary

Aphids are sap-feeding insects that host a range of bacterial endosymbionts including the obligate, nutritional mutualist Buchnera plus several bacteria that are not required for host survival. Among the latter, ‘Candidatus Regiella insecticola’ and ‘Candidatus Hamiltonella defensa’ are found in pea aphids and other hosts and have been shown to protect aphids from natural enemies. We have sequenced almost the entire genome of R. insecticola (2.07 Mbp) and compared it with the recently published genome of H. defensa (2.11 Mbp). Despite being sister species the two genomes are highly rearranged and the genomes only have ∼55% of genes in common. The functions encoded by the shared genes imply that the bacteria have similar metabolic capabilities, including only two essential amino acid biosynthetic pathways and active uptake mechanisms for the remaining eight, and similar capacities for host cell toxicity and invasion (type 3 secretion systems and RTX toxins). These observations, combined with high sequence divergence of orthologues, strongly suggest an ancient divergence after establishment of a symbiotic lifestyle. The divergence in gene sets and in genome architecture implies a history of rampant recombination and gene inactivation and the ongoing integration of mobile DNA (insertion sequence elements, prophage and plasmids).

Ancillary