Thermoplasma acidophilum occurs in self-heating coal refuse piles in southern Indiana and western Pennsylvania. It is found in region of the piles where temperature range from 32 to 80°C and pH ranges from 1.17 to 5.21. As far as is known, this is the only natural habitat. Their cells appear as spheres varying in size from 0.3 to 2.0 µm and, in occasional large cells, up to 5 µm in diameter. T. acidophilum’s cells lack a true cell wall and are surrounded by a single triple layer membrane about 5-10 nm thick. Also, T. acidophilum is gram-negative and its cells are generally immotile. Its optimum temperature for growth is 59°C (max 62°C – min 40°C) and optimum pH 2 (max 4 – min 1).
When grown in liquid medium, basal salt solution is adjusted to pH 2 and supplemented with 0.1% yeast extract and 1.0% glucose. Hydrogen ions are specifically required for maintenance of cellular stability because cells undergo lysis at neutral pH. T. acidophilum requires oxygen and has an absolute requirement for yeast extract for growth and thus far no other compound have been found to substitute it. In the nature, T. acidophilum gets nutrients from the decomposition of organisms killed by the acidity.
T. acidophilum caught the attention of researches because it lives in a particularly harsh environment – hot and acidic – without the protection of a rigid cell wall which is used by other microbes living in similar environments. The genome of T. acidophilum are large chunks of DNA which have been borrowed from other species of microbe and incorporated into the chromosomes. The genes are believed to come from microbes and bacteria that share the same habitat, like the soil near hydrothermal sites. T. acidophilum is used mainly for mineral biooxidation. Mineral biooxidation is a microbial process in which iron sulfide minerals, such as pyrite and arsenopyrite, are degraded by bacteria and precious metals (gold and silver) are liberated for recovery by conventional metallurgical techniques.
References:
Williams, S.T., M.E. Sharpe and J.G. Holt (Editors). 1989. Bergey’s Manual of Systematic Bacteriology. Williams and Wilkins, Baltimore.
Balows, A., H.G. Truper, M. Dworkin, W. Harder and K.H. Schleifer (Editors). 1992.The Prokaryotes, second edition. Springer-Verlag, New York.
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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