Repeated replacement of an intrabacterial symbiont in the tripartite nested mealybug symbiosis

Filip Husnik, John P. McCutcheon

Research output: Contribution to journalArticlepeer-review

156 Scopus citations


Stable endosymbiosis of a bacterium into a host cell promotes cellular and genomic complexity. The mealybug Planococcus citri has two bacterial endosymbionts with an unusual nested arrangement: the aγ-proteobacterium Moranella endobia lives in the cytoplasm of the β-proteobacterium Tremblaya princeps. These two bacteria, along with genes horizontally transferred from other bacteria to the P. citri genome, encode gene sets that form an interdependent metabolic patchwork. Here, we test the stability of this three-way symbiosis by sequencing host and symbiont genomes for five diverse mealybug species and find marked fluidity over evolutionary time. Although Tremblaya is the result of a single infection in the ancestor of mealybugs, the aγ-proteobacterial symbionts result from multiple replacements of inferred different ages from related but distinct bacterial lineages. Our data show that symbiont replacement can happen even in the most intricate symbiotic arrangements and that preexisting horizontally transferred genes can remain stable on genomes in the face of extensive symbiont turnover.

Original languageEnglish (US)
Pages (from-to)E5416-E5424
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number37
StatePublished - Sep 13 2016
Externally publishedYes


  • Horizontal gene transfer
  • Organelle
  • Scale insect
  • Sodalis

ASJC Scopus subject areas

  • General


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