Chlamydia trachomatis

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A Microbial Biorealm page on the genus Chlamydia trachomatis

Classification

Higher order taxa

Bacteria; Chlamydiae/Verrucomicrobia group; Chlamydiae; Chlamydiae (class); Chlamydiales; Chlamydiaceae; Chlamydia

Genus

Chlamydia

NCBI: Taxonomy

Description and significance

Describe the appearance, habitat, etc. of the organism, and why it is important enough to have its genome sequenced. Describe how and where it was isolated. Include a picture or two (with sources) if you can find them.

C. trachomatis is the leading cause of sexually transmitted disease worldwide--in the United States, alone, over 4 million cases are diagnosed each year. It is also the leading cause of preventable blindness (caused by a chlamydia infection called trachoma)in the world.

C. trachomatis is an obligate, aerobic, intracellular parasite of eukaryotic cells. It is a Gram-negative bacteria and has a coccoid or rod shape.

C. trachomatis require growing cells in order to remain viable since it cannot synthesize its own ATP. Without a host organism, C. trachomatis cannot survive on its own.

It is important to understand and sequence the genome of C. trachomatis because it would help us better understand its functions as a pathogen--the properties that allow it to live within its human host and its virulence and biological capabilities as a pathogen. Thus, an effort has been made to sequnce most of the C. trachomatis genome.


SDS - PAGE electrophoresis

Genome structure

Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence? Does it have any plasmids? Are they important to the organism's lifestyle?


Chlamydia trachomatis has a genome that consists of 1,042,519 base pairs and has approximately 894 likely protein coding sequences. C. trachomatis strains have an extrachromosomal plasmid, which was sequenced to be a 7493-base pair plasmid. Because there is less than 1% nucleotide sequnce variation, ll plasmids from human C. trachomatis isolates are considered to be very similar. All the isolates are about 7,500 nucleotides long and has eight open reading frames computer-predicted to code for proteins of more than 100 amino acids, with short non-coding sequences between some of them.

Interestingly, in their nucleotide sequence, chlamydial plasmids are more closely related than is the corresponding chromosomal DNA. The pasmid of C. trachomatis is a favored target for DNA-based diagnosis of C. trachomatis because there are approximately 7-10 copies of the plasmid present per chlamydial particle. Its sequence is highly conserved among different isolates of C. trachomatis. Some C. trachomatis strains lack these plasmids, and the consequences aid in detection of the C. trachomatis strain. Plaque purified C. trachomatis that do not contain the plasmids have unusual inclusion morphology, has no glycogen, and shows no alteration in antibiotic sensitivity . However, the fact that such strains exist shows that the plasmid is not essential for C. trachomatis survival.

Cell structure and metabolism

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

The life cycle of C. trachomatis consists of two stages: elementary body and reticulate body. The elementary body is the dispersal form and is analogous to a spore. It is approximately 0.3 um in diameter and induces its own endocytosis upon exposure to target cells. It is this form that prevents phagolysosomal fusion and hence allows for intracellular survival. Once inside the endosome, the glycogen produced causes the elementary body to "germinate" into the vegetative form, the reticulate body. This form divides by binary fission at approximately 2-3 hours per generation. It has an incubation period of 7-21 days in the host. It contains no cell wall and (when stained with iodine) is detected as an inclusion in the cell. After division, the reticulate body transforms back to the elementary form and is released by the cell by exocytosis. One phagolysosome usually produces 100-1000 elementary bodies.

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.

Chlamydiae replicate intracellularly, within a membrane-bound structure termed an inclusion. It is inside this inclusion, which somehow avoids lysosomal fusion and subsequent degradation, that the metabolically inactive "elementary body" (EB) form of chlamydia becomes the replicative "reticulate body" (RB). The multiplying RBs then become EBs again and burst out of the host cell to continue the infection cycle. Since Chlamydiae are obligate intracellular parasites, they cannot be cultured outside of host cells, leading to many difficulties in research.

Chlamydia is transmitted through infected secretions only. It infects mainly mucosal membranes, such as the cervix, rectum, urethra, throat, and conjunctiva. It is primarily spread via sexual contact and manifests as the sexually transmitted disease. The bacterium is not easily spread among women, so the STD is mainly transmitted by heterosexual or male homosexual contact. However, infected secretions from the genitals to the hands and eventually to the eyes can cause trachoma.

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

Kalman, Sue et al. 1999. Comparative genomes of Chlamydia pneumoniae and C. trachomatis. Nature, 21: 385-389.

chlamydiae.com

Stephens, Richard S. et al. Genome sequence of an obligate intracellular pathogen of humans: Chlamydia trachomatis. Science, 282: 754-759.

T.J. Clark Inc.: Chlamydia trachomatis

Byrne, Gerald I. 2003. Chlamydia uncloaked. PNSA 100:14. 2003

Mohit Singla & Bikram Bal: Infectivity Assays For Chlamydia Trachomatis: The Internet Journal of Microbiology. 2006; Volume 2, Number 2.

Wang, Y. 1999. Etiology of trachoma: a great success in isolating and cultivating Chlamydia trachomatis. Chinese Medical Journal 112, 938 - 941.

Edited by student of Rachel Larsen and Kit Pogliano