Chlamydia trachomatis

Classification

Higher order taxa

Archaea; Euryarchaeota; Thermoplasmata; Thermoplasmatales; Thermoplasmataceae; Thermoplasma

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 an obligate intracellular parasite of eukaryotic cells. It is a Gram-negative bacteria, and has a coccoid or rod shape. It is important to understand and sequnece 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, nearly most of the C. trachomatis genome has been sequenced.

C. trachomatis require growing cells in order to remain viable since Chlamydia trachomatis cannot synthesize its own ATP.

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 chlamydial plasmid has great practical importance. It is a favoured target for DNA-based diagnosis of C. trachomatis infection for two reasons. Firstly, there are approximately 7-10 copies of the plasmid present per chlamydial particle. Its sequence is highly conserved among different isolates of C. trachomatis. There are authenticated examples of C. trachomatis strains lacking the plasmid and it does have effects. Plaque purified C. trachomatis free of the plasmid has unusual inclusion morphology, is glycogen free, 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.

round or occasionally pear shaped, electron-dense structures approximately 0.3 microns in diameter. The Elementary bodies is the only infectious stage of the chlamydial developmental cycle. It functions as a tough "spore-like" body whose purpose is to permit chlamydial survival in the non-supportive (to chlamydiae) environment outside the host cell. The EB is thought to be metabolically inert until it attaches to, and is endocytosed by, a susceptible host cell. It contains only small amounts of the usual bacterial cell wall strengthening substance, peptidoglycan. Instead it derives its strength, among other things, from cross links [-S-S- bridges] formed between the sulphur atoms of its sulphur amino acid rich proteins in the outer envelope.

The reticulate body is the stage of the chlamydial developmental cycle responsible for intracellular replication. Typically, reticulate bodies have a diameter of 1 micron or more and they are non infectious. Reticulate bodies are metabolically active, so their cytoplasm is rich in ribosomes, which are required for protein synthesis. Their nucleic acid appears diffuse and fibrillar. They are bounded by two sets of tri-laminar membranes, an inner cytoplasmic membrane and an external outer envelope, whose surface is covered with projections and rosettes similar to those seen on elementary bodies, but at higher density.

The chlamydial outer membrane complex is composed primarily of three proteins; the major outer membrane protein (MOMP) and two cysteine-rich proteins, the outer membrane complex B protein (OmcB) and the outer membrane complex A protein (OmcA). Chlamydial major outer membrane protein, which by reason of its importance is the most extensively studied, was discovered in 1981 by three independent laboratories

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.

Virulence Factors

There are numerous factors that contribute to the pathogenicity of Chlamydia trachomatis. Colonization of Chlamydia begins with attachment to sialic acid receptors on the eye, throat, or genitalia. It persists at body sites that are inaccessible to phagocytes, T-cells, and B-cells. It also exists as 15 different serotypes. These serotypes cause four major diseases in humans: endemic trachoma (caused by serotypes A and C), sexually transmitted disease and inclusion conjunctivitis (caused by serotypes D and K), and lymphogranuloma venereum (caused by serotypes L1, L2, and L3). Endemic trachoma leads to blindness, whereas inclusion conjunctivitis is associated with the sexually transmitted form and does not lead to blindness. Its unique cell wall structure is another virulence factor. Studies reveal that Chlamydia, because of its cell wall, is able to inhibit phagolysosome fusion in phagocytes. The cell wall is proposed to be gram-negative in that it contains an outer lipopolysaccharide membrane, but it lacks peptidoglycan in its cell wall. This lack of peptidoglycan is shown by the inability to detect muramic acid and antibodies directed against it. It may, however, contain a carboxylated sugar other than muramic acid. The proposed structure consists of a major outer membrane protein cross-linked with disulfide bonds. It also contain cysteine-rich proteins (CRP) that may be the functional equivalent to peptidoglycan. This unique structure allows for intracellular division and extracellular survival (Hatch 1996).

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.

Symptoms due to this contact are quite variable. In fact, 75% of women and 25% of men with Chlamydia show no symptoms at all. In women, symptoms include increased vaginal discharge, burning during urination, irritation of the area around the vagina, bleeding after sexual intercourse, lower abdominal pain, and abnormal vaginal bleeding. Infection in women usually begins at the cervix. In men, non-gonococcal urethritis is the main symptom. This includes clear, white, or yellow discharge from the urethra, burning and pain during urination, and tingling or itching sensations. Another infection caused by C. trachomatis, lymphogranuloma venereum, is characterized by a swelling of the lymph nodes in the groin area. In men, this can lead to proctitis and in women, it can lead to rectal narrowing. The primary stage is detected as small ulcers or vesicles which usually heal without scarring. The secondary stage, called "supperative lymphadenopathy", is characterized by chills, fever, and arthralgais. The large area of swelling in the groin is called a bubo. Finally, the tertiary stage is when rectal narrowing or draining of the sinuses occurs.

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.

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Edited by student of Rachel Larsen and Kit Pogliano