Arsenic is an element that naturally is found in rocks and some soils, and in this insoluble state, it is not harmful to humans or most other forms of life. However, when arsenic is exposed to the air and is oxidized, it forms the toxic compound arsenite which can be further oxidized to the less-toxic arsenate, but in a very slow naturally occurring process.( A New Chemolithoautotrophic…”). Due to medical, agricultural, and industrial uses of arsenic, contamination of drinking water with arsenite throughout the world is a major problem, especially in India, Bangladesh, and the American Midwest (“Aussie Arsenic-eating Bacteria…” and “Genes and Enzymes…”). Fortunately, scientists of Melbourne, Australia have recently discovered Centibacterium arsenoxidans in a gold mine of the Northern Territory of Australia. The particular bacteria is able to oxidize arsenite to arsenate, which will hopefully be able to help purify arsenic-contaminated drinking water (“A New Chemolithoautotrophic…”).
Microorganisms able to oxidize arsenite were first discovered in 1918, but were heterotrophic, as they require the presence of organic matter for growth. In these organisms, the oxidation is probably a detoxification mechanism rather than one that can support growth, even though the reaction is exergonic. However, C. arsenoxidans, discovered in 1999, can grow chemolithoautotrophically with arsenite, oxygen, and carbon dioxide, meaning it can use the energy produced by the oxidation reaction for growth. The doubling time reported for growth of this organism is 7.6 hours, which is much faster than the 2 days doubling time of Pseudomonas arsenitoxidans, the only other known chemolithoautotrophic organism to oxidize arsenite. C. arsenoxidans is able to use arsenite as the electron donor in respiration, oxygen as the terminal electon acceptor, and carbon dioxide or bicarbonate as the carbon source.
C. arsenoxidans is a small microorganism with its size approximately 0.5 by 1.0 micrometers. It a gram-negative rod, motile by two subterminal flagella.
*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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