Defensive bacteriome symbiont with a drastically reduced genome

Curr Biol. 2013 Aug 5;23(15):1478-84. doi: 10.1016/j.cub.2013.06.027. Epub 2013 Jul 11.


Diverse insect species harbor symbiotic bacteria, which play important roles such as provisioning nutrients and providing defense against natural enemies [1-6]. Whereas nutritional symbioses are often indispensable for both partners, defensive symbioses tend to be of a facultative nature [1-12]. The Asian citrus psyllid Diaphorina citri is a notorious agricultural pest that transmits Liberibacter spp. (Alphaproteobacteria), causing the devastating citrus greening disease or Huanglongbing [13, 14]. In a symbiotic organ called the bacteriome, D. citri harbors two distinct intracellular symbionts: a putative nutrition provider, Carsonella_DC (Gammaproteobacteria), and an unnamed betaproteobacterium with unknown function [15], for which we propose the name "Candidatus Profftella armatura." Here we report that Profftella is a defensive symbiont presumably of an obligate nature with an extremely streamlined genome. The genomes of Profftella and Carsonella_DC were drastically reduced to 464,857 bp and 174,014 bp, respectively, suggesting their ancient and mutually indispensible association with the host. Strikingly, 15% of the small Profftella genome encoded horizontally acquired genes for synthesizing a novel polyketide toxin. The toxin was extracted, pharmacologically and structurally characterized, and designated diaphorin. The presence of Profftella and its diaphorin-biosynthetic genes was perfectly conserved in the world's D. citri populations.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacterial Toxins / chemistry
  • Bacterial Toxins / genetics
  • Bacterial Toxins / metabolism
  • Bacterial Toxins / toxicity
  • Betaproteobacteria / genetics*
  • Biological Evolution
  • Cell Line / drug effects
  • Citrus
  • Gammaproteobacteria / genetics*
  • Gene Transfer, Horizontal
  • Genome, Bacterial*
  • Hemiptera / microbiology*
  • Molecular Sequence Data
  • Polyketides / metabolism
  • RNA, Ribosomal, 16S
  • Rats
  • Symbiosis / genetics*
  • Toxicity Tests


  • Bacterial Toxins
  • Polyketides
  • RNA, Ribosomal, 16S

Associated data

  • GENBANK/CP003467
  • GENBANK/CP003468
  • GENBANK/CP003469