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Biology and evolution of Apicomplexa

APICOMPLEXA is a diverse group of protists that includes thousands of obligate intracellular parasites. Members of this group are known to infect virtually every animal phyla, from land, sea and air. In many cases the relationship between the protist and its host is of relatively peaceful coexistence, but in others things go nasty and the consequences are serious, even fatal for the animal host.

Collectively, Apicomplexan parasites constitute a heavy burden for global health and essential resources such as cattle, poultry and other livestock. For example, members of this group are the causative of Malaria in humans (genus Plasmodium), which is responsible for nearly a million deaths each year worldwide. Toxoplasma causes serious congenital diseases and also infects immuno-compromised patients, and Cryptosporidium, causative agent of serious gastrointestinal disease.



We seek to improve our understanding of the apicomplexan parasites by using approaches from Evolutionary Biology: many characteristics of an organism are better understood if they are compared with the corresponding characteristics in evolutionary relatives. Some of the questions we are pursuing are:

  1. improve the resolution of the phylogenetic tree of Apicomplexa
  2. understand the origin and functionality of the mechanisms by which apicomplexan parasites penetrate and invade a host cell
  3. explore the relationships between the parasitic lifestyle, genome and metabolic plasticity
  4. discover “weak points” in their molecular circuits that we can exploit with drugs or vaccines to fight parasitic disease

Ongoing projects

  • We are analysing the transcriptome of Voromonas pontica, a Colpodellid. Colpodellids are free-living basal apicomplexans that feed on other protists by means of a mechanism known as myzocytosis. Because of their phylogenetic position and the characteristics of their feeding habit, colpodellids result of great importance to understand the origin and diversification of the components of the invasion apparatus.
  • We are also working on genomics of Gregarines. These protists are also relatives of colpodellids and apicomplexans and are known to parasitize many invertebrates such as insects and worms. We generated transcriptomic data of Lankesteria abotti, a gregarine that inhabits the digestive system of a small tunicate from the Canadian west coast. Postdoc Banoo Malik-Pightling collected L. abotti cells in Vancouver Island and generated the data.
  • In collaboration with Dr Mary-Beth Saffo (NSF) and Dr. Chris Lane (University of Rhode Island) we are generating and analyzing genomic data of Nephromyces, a particularly interesting protist that inhabits the renal sac of Molgulid tunicates from the east coast (USA and Canada). Unlike other apicomplexans, Nephromyces does not appear to be a pathogen to its host. Rather, protist and tunicate could have established a symbiotic relationship of mutual benefit. We expect to find in Nephromyces clues to understand the molecular basis of the limits between parasitism and mutualism.
  • We are now starting to use the ciliate model Tetrahymena thermophila to investigate the function of certain genes that are shared by the three lineages of alveolates (ciliates, apicomplexans and dinoflagellates) and could constitute good targets for drug discovery against malaria and other diseases caused by apicomplexan parasites.

Current view of the evolutionary relationships among alveolates, with emphasis on apicomplexans and their relatives.

Image from Obornik et al., 2012, Protist 163(2):306-323

Image from Obornik et al., 2012, Protist 163(2):306-323