| Giardia | |
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| Giardia trophozoite, SEM | |
| Scientific classification | |
| Domain: | Eukaryota |
| (unranked): | Excavata |
| Phylum: | Metamonada |
| Order: | Diplomonadida |
| Family: | Hexamitidae |
| Genus: | Giardia Kunstler, 1882 |
| species | |
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Giardia agilis |
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Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" (named for the excavated groove on one side of the cell body) that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis. Their life cycle alternates between an actively swimming trophozoite and an infective, resistant cyst. The genus was named after French zoologist Alfred Mathieu Giard.
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Characteristics
Like other diplomonads, Giardia have two nuclei, each with four associated flagella, and lack both mitochondria and a Golgi apparatus. However they are now known to possess mitochondrial relics, called mitosomes. These are not used in ATP synthesis the way mitochondria are, but are involved in the maturation of iron-sulfur proteins.[1] The synapomorphies of genus Giardia include cells with duplicate organelles, absence of cytostomes, and ventral adhesive disc[2]
Systematics
About 40 species have been described from different animals, but many of them are probably synonyms[3]. Currently, five to six morphologically distinct species are recognised[4]. Giardia lamblia (=G. intestinalis, =G. duodenalis) infect humans and other mammals, G. muris is found from other mammals, G. ardeae and G. psittaci from birds, G. agilis from amphibians and G. microti from voles [5]. Other described, (but not certainly valid) species include:
- Giardia beckeri
- Giardia beltrani
- Giardia botauri
- Giardia bovis
- Giardia bradypi
- Giardia canis
- Giardia caprae
- Giardia cati
- Giardia caviae
- Giardia chinchillae
- Giardia dasi
- Giardia equii
- Giardia floridae
- Giardia hegneri
- Giardia herodiadis
- Giardia hyderabadensis
- Giardia irarae
- Giardia marginalis
- Giardia melospizae
- Giardia nycticori
- Giardia ondatrae
- Giardia otomyis
- Giardia pitymysi
- Giardia pseudoardeae
- Giardia recurvirostrae
- Giardia sanguinis
- Giardia serpentis
- Giardia simoni
- Giardia sturnellae
- Giardia suricatae
- Giardia tucani
- Giardia varani
- Giardia viscaciae
- Giardia wenyoni
[6]. Genetic and biochemical studies have revealed the heterogeneity of Giardia lamblia, which contains probably at least eight lineages or cryptic species[7].
Genome
A Giardia isolate (WB) was the first diplomonad to have its genome sequenced. It has a 11.7 million basepair genome is compact in structure and content with simplified basic cellular machineries and metabolism. Currently the genomes of several other Giardia isolates and diplomonads (the fish pathogens Spironucleus vortens and S. salmonicida) are being sequenced. [8]
See also
References
- ^ Tovar J. et al. (2003). "Mitochondrial remnant organelles of Giardia function in iron-sulphur protein maturation". Nature 13 (426 (6963)): 172-6. doi:. PMID 14614504.
- ^ Cepicka, Ivan. 2008. Fornicata. Version 02 September 2008 (under construction). http://tolweb.org/Fornicata/121182/2008.09.02 in The Tree of Life Web Project, http://tolweb.org/
- ^ Meyer E.A., Radulescu S. (1979). "Giardia and Giardiasis". Advances in Parasitology 17: 1-47. doi:. PMID 395833.
- ^ R.C.Brusca, G.J.Brusca. Invertebrates. Sinauer Associates, 2 ed.(2003)
- ^ Adam,R.D. Biology of Giardia. Clinical Microbiology Reviews, July 2001, p. 447–475
- ^ Tree of Life Web Project. 2008. Giardia Kunstler. Version 02 September 2008 (temporary). http://tolweb.org/Giardia/97370/2008.09.02 in The Tree of Life Web Project, http://tolweb.org/
- ^ R.C.A. Thompson and P.T. Monis, Variation in Giardia: implications for taxonomy and epidemiology. Advances in Parasitology 58, 69-137 (2004)
- ^ Andersson, JO et al. (2010). "The Genome of Giardia and Other Diplomonads". Anaerobic Parasitic Protozoa: Genomics and Molecular Biology. Caister Academic Press. ISBN 978-1-904455-61-5.
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