Genome history in the symbiotic hybrid Euglena gracilis

Gene. 2007 Nov 1;402(1-2):35-9. doi: 10.1016/j.gene.2007.07.023. Epub 2007 Aug 2.


Euglena gracilis has a chimeric gene collection in which some genes were inherited from its heterotrophic host and others were acquired from a photoautotrophic endosymbiont during secondary endosymbiosis. The evolutionary reconstruction of such a hybrid genome poses a challenge for standard phylogenetic tools that produce bifurcating trees because genome evolution by endosymbiotic gene transfer is a non tree-like process. We sequenced 2770 ESTs from E. gracilis, of which 841 have homologues in a sample of other eukaryotes. Most of these homologues are found in all of the eukaryotes in our sample, but 117 of them are specific to photoautotrophic eukaryotes. A phylogenetic tree fails to account for this observation but the distribution of homologues and a phylogenetic network clearly show the common origin of E. gracilis from both kinetoplastid and photoautotrophic ancestors.

MeSH terms

  • Animals
  • Chimera / genetics*
  • Chimera / metabolism
  • DNA, Complementary / metabolism
  • Euglena gracilis / genetics*
  • Euglena gracilis / metabolism
  • Evolution, Molecular
  • Genome*
  • Humans
  • Phylogeny
  • Symbiosis / genetics*


  • DNA, Complementary