Mycobacteria: Biology


The bacterial genus Mycobacterium contains more than 120 members, several of which are extremely successful pathogens of man and animals including the agents of tuberculosis and leprosy. All mycobacteria are aerobic, nonmotile, nonspore forming, Gram‐positive bacteria with a high genomic guanine + cytosine (GC) content. They possess a thick cell wall that contains unique lipids, called mycolic acids, which confer a characteristic acid‐fast staining property and make the genus hardy and resistant to antimicrobials and host defences.

Keywords: mycobacteria; tuberculosis; leprosy; acid‐fast; Robert Koch

Figure 1.

A phylogenetic tree showing a selection of the mycobacteria. The tree was calculated based on the similarity of the mycobacterial 16s rRNA gene sequences. A clear separation of the fast and slow growers (grey shading) is apparent. Tree created using the tree builder tool and 16s rRNA gene sequences from the Ribosomal Database Project ( Strain name is followed by the strain designation (‘T’ indicates a Type Strain) and 16s rRNA gene accession numbers. The tree is rooted using Nocardia farcinica ATCC 3318 (X80595).

Figure 2.

The cell and colony morphology of M. smegmatis is typical of that of many mycobacteria. (a) depicts the characteristic rod shape of M. smegmatis shown expressing the (GFP), visualized using confocal microscopy. The cells are ∼10 μm long (Taken by B. Sidders, RVC). (b) depicts M. smegmatis colonies growing on solid agar and the differences that can be seen in colony morphology. Colonies shown are growing in the presence (left) and absence (right) of glycerol (Courtesy of S. Kendall, RVC).

Figure 3.

The mycobacterial cell wall. The mycobacteria possess a uniquely thick, lipid‐rich cell wall that forms a near impermeable barrier. Atop a typical Gram‐positive membrane is the MAP complex, consisting of (PG) linked to (AG) which acts to anchor the mycolic acids in place. Outside this are a layer of ‘free’ or covalently bound lipids including the (PDIMs), (PGLs), etc. The mycobacteria are also surrounded by a loosely attached capsule made of various polysaccharides. Interspersed through all of this are various cell wall proteins (porins, etc.) and components such as (LAM, shown) a major glycolipid that plays a key role in modulating the host–immune response.


Further Reading

Brosch R, Gordon SV, Marmiesse M et al. (2002) A new evolutionary scenario for the Mycobacterium tuberculosis complex. Proceedings of the National Academy of Sciences of the USA 99(6): 3684–3689.

Cole ST, Eisenach KD, McMurray DN, and Jacobs WR Jr (eds) (2005) All chapters. In: Tuberculosis and the Tubercle Bacillus. Washington, USA: ASM Press.

Madigan MT and Martinko J (eds) (2006) Actinobacteria: mycobacterium. In: Brock: Biology of Microorganisms, 11th edn, pp. 388–390. New Jersey, USA: Pearson Prentice‐Hall.

Pym AS, Gordon SV and Brosch R (2006) Pathogenomics: insights into tuberculosis and related mycobacterial diseases. In: Hacker J and Dobrindt U (eds) Pathogenomics: Genome Analysis of Pathogenic Microbes, pp. 211–230. Weinheim, Germany: Wiley.

Wayne LG and Kubica GP (1986) The mycobacteria. In: Sneath P and Holt J (eds) Bergey's Manual of Systemic Bacteriology, vol. 2, pp. 1435–1457. Baltimore, MD: Williams & Wilkins.

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Sidders, Ben, and Stoker, Neil G(Sep 2007) Mycobacteria: Biology. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0020389]