Chlamydiae
Encyclopedia
Chlamydiae is a bacterial phylum and class
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...

 whose members are obligate intracellular pathogens. Many Chlamydiae coexist in an asymptomatic
Asymptomatic
In medicine, a disease is considered asymptomatic if a patient is a carrier for a disease or infection but experiences no symptoms. A condition might be asymptomatic if it fails to show the noticeable symptoms with which it is usually associated. Asymptomatic infections are also called subclinical...

 state within specific hosts
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...

, and it is widely believed that these hosts provide a natural reservoir for these species.

All known Chlamydiae only grow by infecting eukaryotic host cells. They are as small or smaller than many virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

es. Chlamydiae replicate inside the host cells and are termed intracellular
Intracellular
Not to be confused with intercellular, meaning "between cells".In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".It is used in contrast to extracellular...

. Most intracellular Chlamydiae are located in an inclusion body or vacuole. Outside of cells they survive only as an extracellular
Extracellular
In cell biology, molecular biology and related fields, the word extracellular means "outside the cell". This space is usually taken to be outside the plasma membranes, and occupied by fluid...

 infectious form. Chlamydiae can grow only where their host cells grow. Therefore, Chlamydiae cannot be propagated in bacterial culture media in the clinical laboratory. Chlamydiae are most successfully isolated while still inside their host cell.

Cavalier-Smith
Thomas Cavalier-Smith
Professor Thomas Cavalier-Smith , FRS, FRSC, NERC Professorial Fellow, is a Professor of Evolutionary Biology in the Department of Zoology, at the University of Oxford...

 has postulated that the Chlamydiae fall into the clade Planctobacteria
Planctobacteria
Planctobacteria is a taxon created by Cavalier-Smith, specifically a division Historically bacteria were considered plants consequently the usage of "division" over "phylum" was brought over when the kindgom Monera was established. The bacteriological code has since imposed that the rank should be...

 in the larger clade Gracilicutes
Gracilicutes
Gracilicutes is a controversial taxon in Bacterial taxonomy.Traditionally Gram staining results were most commonly used as a classification tool, consequently until the advent of molecular phylogeny, the Kingdom Prokaryotae was divided into four divisions,*...

.

History

Chlamydia-like disease affecting the eyes of people was first described in ancient Chinese and Egyptian manuscripts. A modern description of Chlamydia-like organisms was provided by Halberstaedter and von Prowazek
Stanislaus von Prowazek
Stanislaus Josef Mathias von Prowazek, Edler von Lanow , born Stanislav Provázek, was a Czech zoologist and parasitologist, who along with pathologist Henrique da Rocha Lima discovered the pathogen of epidemic typhus.Prowazek had studied epidemic typhus in Serbia and Istanbul...

 in 1907. Chlamydial isolates cultured in the yolk sacs of embryonating eggs were obtained from a human pneumonitis
Pneumonitis
Pneumonitis or pulmonitis is a general term that refers to inflammation of lung tissue.Pneumonia is pneumonitis combined with consolidation and exudation...

 outbreak in the late 1920s and early 1930s, and by the mid-20th Century isolates had been obtained from dozens of vertebrate species. The term Chlamydia (a cloak) appeared in the literature in 1945, although other names continued to be used, including Bedsonia, Miyagawanella, ornithosis-, TRIC-, and PLT-agents.

Nomenclature

In 1966, Chlamydiae were recognized as bacteria and the genus Chlamydia
Chlamydia (bacterium)
Chlamydia is a genus of bacteria that are obligate intracellular parasites. Chlamydia infections are the most common bacterial sexually transmitted infections in humans and are the leading cause of infectious blindness worldwide....

was validated. The Order Chlamydiales
Chlamydiales
The bacterial order Chlamydiales includes only obligately intracellular bacteria that have a chlamydia-like developmental cycle of replication and at least 80% 16S rRNA or 23S rRNA gene sequence identity with other members of Chlamydiales. Chlamydiales live in animals, insects, and protozoa...

 was created by Storz and Page in 1971. Between 1989 and 1999, new families, genera, and species were recognized. The phylum Chlamydiae was established in Bergey's Manual of Systematic Bacteriology.

By 2006, genetic data for over 350 chlamydial lineages had been reported, four chlamydial families had been recognized (Chlamydiaceae
Chlamydiaceae
Chlamydiaceae is a family of bacteria that belongs to the Phylum Chlamydiae, Order Chlamydiales. All Chlamydiaceae species are Gram-negative and express the family-specific lipopolysaccharide epitope αKdo--αKdo--αKdo . Chlamydiaceae ribosomal RNA genes all have at least 90% DNA sequence identity...

, Parachlamydiaceae
Parachlamydiaceae
Parachlamydiaceae is a family of bacteria in the order Chlamydiales. Species in this family have a Chlamydia–like cycle of replication and their ribosomal RNA genes are 80–90% identical to ribosomal genes in the Chlamydiaceae. The Parachlamydiaceae naturally infect amoebae and can be grown in...

, Simkaniaceae
Simkaniaceae
Simkaniaceae is a family of bacteria in the order Chlamydiales, class Chlamydiae, phylum Chlamydiae, domain Bacteria. Species in this family have a chlamydia-like cycle of replication and their ribosomal RNA genes are 80–90% identical to ribosomal genes in the Chlamydiaceae...

, and Waddliaceae
Waddliaceae
Waddlia is a genus of bacteria in its own family, Waddliaceae. Species in this genus have a Chlamydia-like cycle of replication and their ribosomal RNA genes are 80–90% identical to ribosomal genes in the Chlamydiaceae....

), and another family had been proposed (Rhabdochlamydiaceae
Rhabdochlamydiaceae
Candidatus Rhabdochlamydia is a genus of intracellular bacteria; a separate family, Candidatus Rhabdochlamydiaceae, has been proposed for this genus. Candidatus Rhabdochlamydia species have not been cultured in vitro and have not been deposited in culture collections.Two Rhabdochlamydia species...

).

Genomics

Chlamydiae is a unique bacterial evolutionary group that separated from other bacteria approximately a billion years ago. Reports have varied as to whether Chlamydiae is related to Planctomycetales or Spirochaetes. Genome sequencing, however, indicates that 11% of the genes in Candidatus Protochlamydia amoebophila UWE25 and 4% in Chlamydiaceae
Chlamydiaceae
Chlamydiaceae is a family of bacteria that belongs to the Phylum Chlamydiae, Order Chlamydiales. All Chlamydiaceae species are Gram-negative and express the family-specific lipopolysaccharide epitope αKdo--αKdo--αKdo . Chlamydiaceae ribosomal RNA genes all have at least 90% DNA sequence identity...

 are most similar to chloroplast
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...

, plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

, and cyanobacterial genes. Comparison of ribosomal RNA
Ribosomal RNA
Ribosomal ribonucleic acid is the RNA component of the ribosome, the enzyme that is the site of protein synthesis in all living cells. Ribosomal RNA provides a mechanism for decoding mRNA into amino acids and interacts with tRNAs during translation by providing peptidyl transferase activity...

 genes has provided a phylogeny of known strains within Chlamydiae. The unique status of Chlamydiae has enabled the use of DNA analysis for chlamydial diagnostics.

There are three described species of chlamydiae that commonly infect humans:
  • Chlamydia trachomatis
    Chlamydia trachomatis
    Chlamydia trachomatis, an obligate intracellular human pathogen, is one of three bacterial species in the genus Chlamydia. C. trachomatis is a Gram-negative bacteria, therefore its cell wall components retain the counter-stain safranin and appear pink under a light microscope.The inclusion bodies...

    , which causes the eye-disease trachoma
    Trachoma
    Trachoma is an infectious disease causing a characteristic roughening of the inner surface of the eyelids. Also called granular conjunctivitis and Egyptian ophthalmia, it is the leading cause of infectious blindness in the world...

     and the sexually transmitted infection chlamydia;
  • Chlamydophila pneumoniae
    Chlamydophila pneumoniae
    Chlamydophila pneumoniae is a species of Chlamydophila, an obligate intracellular bacteria that infects humans and is a major cause of pneumonia....

    , which causes a form of pneumonia
    Pneumonia
    Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...

    ;
  • Chlamydophila psittaci
    Chlamydophila psittaci
    Chlamydophila psittaci is a lethal intracellular bacterial species that may cause endemic avian chlamydiosis, epizootic outbreaks in mammals, and respiratory psittacosis in humans. Chlamydophila psittaci is transmitted by inhalation, contact or ingestion among birds and to mammals...

    , which causes psittacosis
    Psittacosis
    In medicine , psittacosis — also known as parrot disease, parrot fever, and ornithosis — is a zoonotic infectious disease caused by a bacterium called Chlamydophila psittaci and contracted from parrots, such as macaws, cockatiels and budgerigars, and pigeons, sparrows, ducks, hens, gulls and many...

    .

Phylogeny

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LSPN) and the phylogeny is based on 16S rRNA-based LTP release 106 by The All-Species Living Tree Project 
Notes:

♠ Strains found at the National Center for Biotechnology Information
National Center for Biotechnology Information
The National Center for Biotechnology Information is part of the United States National Library of Medicine , a branch of the National Institutes of Health. The NCBI is located in Bethesda, Maryland and was founded in 1988 through legislation sponsored by Senator Claude Pepper...

 (NCBI) but not listed in the List of Prokaryotic names with Standing in Nomenclature (LSPN)

External links

  • Chlamydiae.com, a comprehensive information source from Dr. Michael Ward (Professor of Medical Microbiology in the University of Southampton)
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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