Mycobacterium tuberculosis: Difference between revisions

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''Mycobacterium tuberculosis''is 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)
''Mycobacterium tuberculosis''is 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.  
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).
''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).

Revision as of 09:07, 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.

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).

M. tuberculosis could be isolated in labs, and the most commonly used strain of M. tuberculosisis the H37Rv strain.

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 G+C content is about 65% (NCBI).

The genome of M. tuberculosis was studied generally using the strain M. tuberculosis H37Rv. The genome contains about 4000 genes. Genes that code for lipid metabolism are a very important part of the bacterial genome, and 8% of the genome is involved in this activity. (2919)

The different 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 the speices. So some scientists suggest that they should be grouped as a single species while others argue that they should be grouped as varieties or subspecies of M. tuberculosis. ()

Plasmids in M. tuberculosis is important in transferring virulence because genes on the plasmids are more easily transferred than genes located on the chromosome (plasmid), one such 18kb plasmid in the M. tuberculosis H37Rv strain was proven to conduct gene transfers.

Cell structure and metabolism

The M. tuberculosis cell wall contains three classes of mycolic acids: alpha-, keto- and methoxymycolates. The cell wall also contains lipid complexes including acyl glcolipids and other complex such as 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. (1475)

M. tuberculosis pathogenesis involves genes used for biosynthesis of the mycobacterial cell envelope. The mycobacterial cell envelope consists of a lipids and glycolipids that forms a hydrophobic barrier, in which specific cell envelope lipids activates or represes host innate immune response. (166) For example colvalently linked to the mycolic acids are Glycolipid trehalose dimycolate (TDM), which is composed of nonreducing sugar trehalose. The structure differences of the TDM influence the host animal biological response.(1475)

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. To survive for a prolonged period in the host, M, tuberculosis had learned to adapt to the environment by allowing or inhibiting transcription according to its surroundings (6449).

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