Giardia lamblia: Difference between revisions

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G. lamblia possess two equal-sized nuclei, each contains an entire genome of equal sizes (Yu et al, 2002). Both nuclei are transcriptionally active and are replicated simultaneously during cell division. (Adam, 2001).  
G. lamblia possess two equal-sized nuclei, each contains an entire genome of equal sizes (Yu et al, 2002). Both nuclei are transcriptionally active and are replicated simultaneously during cell division. (Adam, 2001).  


The G. lamblia genome consists of 1.2 million base pairs, distributed among five linear chromosomes, each are flanked by the telomere sequence (5’TAGGG3’) comparable to other eukaryotes (Le Blancq et al, 1991). Chromosome packing is done by core histones, but the mechanism is slightly different from other eukayotes (Yee et al, 2007). [See also [[Current Research||Current Research]]].
The G. lamblia genome consists of 1.2 million base pairs, distributed among five linear chromosomes, each are flanked by the telomere sequence (5’TAGGG3’) comparable to other eukaryotes (Le Blancq et al, 1991). Chromosome packing is done by core histones, but the mechanism is slightly different from other eukayotes (Yee et al, 2007). [See also [[Current Research|Current Research]]].
   
   
The genome has an average GC content of 46% (<a href="www.mbl.edu/Giardia">Giardia lamblia genome project</a>). Complete mapping of the G. lamblia genome (WB strain) is in progress (95% complete, as of 2007 August), using shotgun sequencing. So far 6488 open reading frames (ORF) are predicted, of which 4746 are transcribed.  
The genome has an average GC content of 46% ([http://www.mbl.edu/Giardia Giardia lamblia genome project]). Complete mapping of the G. lamblia genome (WB strain) is in progress (95% complete, as of 2007 August), using shotgun sequencing. So far 6488 open reading frames (ORF) are predicted, of which 4746 are transcribed.  


Nevertheless, studies have been conducted based on the partial genome. Its comparison among other eukaryotic species has provided new perspective in the evolution of this species.
Nevertheless, studies have been conducted based on the partial genome. Its comparison among other eukaryotic species has provided new perspective in the evolution of this species.

Revision as of 08:41, 29 August 2007

A Microbial Biorealm page on the genus Giardia lamblia

Classification

Higher order taxa

Domain Eukaryota
(Unspecified rank) Diplomonadida group
(Unspecified rank) Diplomonadida
Family Hexamitidae
Sub-family Giardiinae
Genus Giardia

Species

Species: Giardia lamblia
Other names: Giardia intestinalis, Giardia duodenalis

NCBI: [1]


Description and significance

Giardia lamblia is a flagellated, microaerophilic microorganism, first discovered by Van Leeuwenhoek in 1681, who found it in his own diarrheal stool. The G. lamblia trophozite, vegetative, motile form of G. lamblia is pear-shaped and have unique morphology such as two identical nuclei, a ventral disc for adhesion to the host intestine, and flagella [see also Structure]. The cyst is the reproductive form, and consists of a protective cyst wall as well as four nuclei.

The genus Giardia has been isolated from more than 40 species. The species G. lamblia is known to infect human, mammals, reptiles, and birds, cows, sheeps and pigs, depending on the strain (Adam 2001).

G. lamblia is one of the major cause of waterborne diseases worldwide (CDC, 2004), and infection results in giardiasis (characterized by malabsorption and severe diarrhea). Giardia-induced intestinal infection is particularly severe in developing world, where giardiasis occurrence relates heavily to water source contamination. In the united states, G. lamblia has been found in both drinking and recreational water. Due to the high prevalence of giardiasis, G. lamblia is of significant interest in the clinical research community. However the pathogenic mechanisms are not completely understood. [See also Pathology].

G. lamblia is also significant in evolutionary biology. Due to its lack of mitochondria, G. lamblia is believed to be diverged from one of the earliest lineages of eukaryotes before the endosymbiotic relationship of mitochondria began (the kingdom name “Archezoa” has been proposed). However, this theory is currently under debate. Emerging proofs in genetics, for example, by comparison of the gene encoding valyl-tRNA synthetase (Hashimoto et al, 1998) and discovery of complex cellular machineries, (such as localized, mitochondria-like electron-transport machinery, (Lloyd, 2002)) suggest they may be more advanced organisms, who were once mitochondria-bearing but lost them ever since. Sequencing of the complete genome of G. lambdia is current in progress, but results so far have already provided much insight into its evolutionary history.

Genome structure

G. lamblia possess two equal-sized nuclei, each contains an entire genome of equal sizes (Yu et al, 2002). Both nuclei are transcriptionally active and are replicated simultaneously during cell division. (Adam, 2001).

The G. lamblia genome consists of 1.2 million base pairs, distributed among five linear chromosomes, each are flanked by the telomere sequence (5’TAGGG3’) comparable to other eukaryotes (Le Blancq et al, 1991). Chromosome packing is done by core histones, but the mechanism is slightly different from other eukayotes (Yee et al, 2007). [See also Current Research].

The genome has an average GC content of 46% (Giardia lamblia genome project). Complete mapping of the G. lamblia genome (WB strain) is in progress (95% complete, as of 2007 August), using shotgun sequencing. So far 6488 open reading frames (ORF) are predicted, of which 4746 are transcribed.

Nevertheless, studies have been conducted based on the partial genome. Its comparison among other eukaryotic species has provided new perspective in the evolution of this species.

Studies by comparing upstream sequence to cytoskeletal protein-coding genes have found several consensus sequence, for example, an AT-rich region 5’AATTAAAAA3’ found between –30 and –70 upstream. These sequences have been proposed as promoter regions for G. lamblia, although they are relatively shorter than that of other eukaryotes. The AT-rich region shown above has been found to be essential for transcription. In addition, recent studies have shown that G. lamblia promoters, in particular, the AT-rich, “TATA”-like regions, cause the production of sterile anti-sense transcripts (Teodorvic et al, 2007).

Genes coding for homologs of mitochondrial proteins such as heat shock protein 70 and chaperonin 60 (cpn60) have been identified in the G. lamblia genome (Roger et al, 1998) and the expression has been found throughout the entire life cycle except during excystation. This suggests that the Gardia was not pre-mitochondrial, but incorporated the mitochondrial ancestor but lost them ever since. In the same context, genes encoding for valy-tRNA synthetase (ValRS), which are believed to be originated from the mitochondria, have also been found in the G. lamblia genome (Hashimoto et al, 1998).

Cell structure and metabolism

Describe any interesting features and/or cell structures; how it gains energy; what important molecules it produces.

Ecology

Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.

Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

Current Research

Enter summaries of the most recent research here--at least three required

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by student of Rachel Larsen