Mycobacterium tuberculosis: Difference between revisions

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==Genome structure==
==Genome structure==
''Mycobacterium tuberculosis'' has a circular DNA about 4,200,000 nucleotides long. The GC content is about 65%.  
''Mycobacterium tuberculosis'' has a circular chromosomes of about 4,200,000 nucleotides long. The GC content is about 65%.  
 
The genome of M. tuberculosis was studied generally using the straing M. tuberculosis H37Rv. The genome contains about 4000 genes. Lipid metabolism is important and 8% of the genome is involved in this activity. (2919)


The four speices of the ''mycobacterium tuberculosis'' complex show a 95-100% DNA relatedness based on studies of DNA homology, and the sequence of the 16S rRNA gene are exactly the same for all five species. So some scientists should be grouped as a single speices while others argue that they should be grouped as varieties or subspecies of ''M. tuberculosis''.
The four speices of the ''mycobacterium tuberculosis'' complex show a 95-100% DNA relatedness based on studies of DNA homology, and the sequence of the 16S rRNA gene are exactly the same for all five species. So some scientists should be grouped as a single speices while others argue that they should be grouped as varieties or subspecies of ''M. tuberculosis''.

Revision as of 08:46, 5 June 2007

A Microbial Biorealm page on the genus Mycobacterium tuberculosis

Classification

Higher order taxa

Domain: Bateria; Phylum: Actinobacteria; Class: Actinobacteria; Order: Actinomycetales; family: Mycobacteriaceae; Genus: Mycobacterium

Species

The mycobacterium tuberculosis complex (MTC) consists of Mycobacterium africanum, Mycobacterium bovis, Mycobacterium canettii, Mycobacterium microti, Mycobacterium tuberculosis.

Description and significance

Mycobacterium tuberculosisis acid fast bacteria, which can form acid-stable complexes when certain arylemtahne dyes are added (217). All species of mycobacteria has ropelike structures of peptidoglycan that are arranged in such a way to give them properties of a acid fast bacteria (217) Mycobacteria are abundant in soil and water, but it is mainly identified as a pathgoen that lives in the host, and some species in its Mycobacterium tuberculosis complex had adapted its genetic structure to be specific to infect human populations. The Mycobacterium tuberculosis forms a complex with other higher related bacteria called the M. tuberculosis complex that consists of 6 members: M. tuberculosis and Mycobacterium africanmum, which infect humans; Mycobacterium microti, which infects vole; Mycobacterium bovis, which infects other mamlian species as well as humans; M. bovis BCG, a variant of Mycobacterium bovis and Mycobacterium canettii, a pathogen that infects humans. (2919)

M. tuberculosis have very simple growth requirements and are able to grow slowly in harsh conditions. Their acid-fast property is the strongest when there is glycerol around. However, when glucose is the main source of nutrient, the utilization of glycerol by M. tuberculosis is inhibited. Therefore, it’s been shown that glutatmate, and not glucose, is actually the main source of nutrient for initating growth (217).

Since as many as 32% of the human population is affected by Tubercolsis (TB), a disease caused by infection of M. tuberculosis in one way or another, and about 10% of them becomes ill per year (3707), it is not hard to see the significance in understanding the genomes of the pathogen to develop and improve strategies for treatment by developing specific drugs that target the genes products of M. tuberculosis.

Genome structure

Mycobacterium tuberculosis has a circular chromosomes of about 4,200,000 nucleotides long. The GC content is about 65%.

The genome of M. tuberculosis was studied generally using the straing M. tuberculosis H37Rv. The genome contains about 4000 genes. Lipid metabolism is important and 8% of the genome is involved in this activity. (2919)

The four speices of the mycobacterium tuberculosis complex show a 95-100% DNA relatedness based on studies of DNA homology, and the sequence of the 16S rRNA gene are exactly the same for all five species. So some scientists should be grouped as a single speices while others argue that they should be grouped as varieties or subspecies of M. tuberculosis.

Cell structure and metabolism

The M. tuberculosis cell wall contains three classes of mycolic acids: -, keto-, and methoxymycolates, where -Mycolates are the most abundant form in M. tuberculosis. The cell wall also contains lipid complexes include acyl glcolipids and other complext free lipids and sulfolipids. There are porins in the membrane to facilitate transport. Beneath the cell wall, there are layers of arabinogalactan and peptidoglycan that lie just above the plasma membrane.

The M. tuberculosis genomes encodes about 190 transcriptional regulators, including sigma factors. Several regulators have been found to respond to environmental distress, such as extreme cold or heat, iron starvation, and oxidative stress.

Ecology

Mycobacterium tuberculosis has been found in early hominids origniated in East-Africa. Therefore, studying the population structure of the species might provide insights about homo sapiens's migratory and emographic history. Mycobacterium tuberculosis has also been known to be drug resistance. Understanding the biology of drug resistance enables researchers to predict and prevent furture spread of resistant strains.

Pathology

Mycobacterium tuberculosis infects both human and non-human primates as well as other animals such as dogs, cats, pigs birds and wild animals by producing pili that are recognized by IgG antibodies. Once inside the host cell, it is able to survive and replicate within the macrophages of the host by avoidng lysosomal fusion with the mycobacteria-containing phagosome. However, most of the host-microbe interaction is unknown.

Application to Biotechnology

Gene for histone-like protein (hupB [Rv2986c]) of Mycobacterium tuberculosis had been used to dinstinguishing members of the MTB complex from other mycobaacterial species and differentiating between members within the complex.

In addition, in vivo complementation in mycobacterium tuberculosis strain H37Ra can be used to identify genomic fragment associated with virulence.

Current Research

Since the pathogen-host interaction of Mycobacterium tuberculosis is still unknown, much of the current research is geared towards the understanding of the mechanism of virulence. For example, one such research showed that prokaryotic- and eukaryotic-like isoforms of the glyozxylate cycle enzyme isocitrate lyase (ICL) are jointly required for fatty acid catabolism and virulence in Mycobacterium tuberculosis. This discovery provide insight such as drugs that are glycoxylate cycle inhibitors could be used to treat tuberculosis.

References

Christopher J. A., Juan ., Sonja Hess, Guillermo C., Jorge A. G., and Richard L. F. Mycobacterium tuberculosis produces pili during human infection.Proc Natl Acad Sci U S A. 2007;104(12): 5145–5150.

Ernesto J. M. and John D. M. Lee W. R. M. tuberculosis isocitrate lyases 1 and 2 are jointly required for in vivo growth and virulence. Nat Med. 2005 June; 11(6): 638–644.

Of mice, men, and elephants: Mycobacterium tuberculosis cell envelope lipids and pathogenesis. J. Clin. Invest., Jun 2006; 116: 1475 - 1478.

Pascopella L, Collins FM, Martin JM, Lee MH, Hatfull GF, Stover CK, Bloom BR, Jacobs WR Jr. Use of in vivo complementation in Mycobacterium tuberculosis to identify a genomic fragment associated with virulence. Infect Immun. 1994;62:1313–1319. [PubMed]


Edited by Ying Liu of Rachel Larsen and Kit Pogliano