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Journal Club:”A Bacterium That Can Grow by Using Arsenic Instead of Phosphorous”

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Since the previous journal club where we covered an article that looked at the microbial synthesis of alkanes, another a curious observation made the rounds in the science world. In the latest Science Journal, Felisa Wolfe-Simon et. al. report their successful isolation of a bacteria that can use arsenic instead of phosphorous.

The group isolated the bacterial strain called, GFAJ-1, by inoculating synthetic media containing glucose, vitamins and trace metals and varying concentrations of AsO43- with sediments from Mono Lake which naturally contains high concentrations of dissolved arsenic (200 M) and performing many serial dilutions. GFAJ-1 was identified to belong to Halomonadaceae family of Gammaproteobacteria.


Various tests were performed to verify that these organisms could not only live but procreate in this environment. Among the remarkable features of this organism is the observation that arsenic can get incorporated into macromolecules most notably DNA where it replaces the need for phosphorous in the backbone. Despite similar chemical properties of AsO43-and PO43- down-stream processes can be affected by the presence of AsO43-explaining the toxic effects of arsenate. It is even more remarkable that this bacterium can switch between the use of AsO43- and PO43-although it has to be noted that the organisms grow much faster in media containing phosphate instead of arsenate. Details on how arsenic was incorporated into macromolecules and how the organism can deal with varying concentrations of arsenic and phosphorus are currently unknown but will surely be part of future publications.


Why is this so important?


There has been the long-standing view that life on earth is mostly based on carbon, hydrogen, nitrogen, oxygen sulfur and phosphorus. The observation that phosphorus which builds the backbone of DNA can be replaced by arsenic expands the view of possible biochemistry that can take place in other parts of the universe.


From an environmental point of view, dissolved arsenic is toxic to most life due to the similar but but not quite identical properties of arsenic which allows some reactions to take place while inhibiting others. Could bio accumulation of arsenic by used to clean up arsenic contamination sites? 


P.S (2011-02-18).: The journal club would not be complete if I did not mention that some people remain skeptical of the claim that arsenate can replace phosphate in these organisms. The criticicsm centers around some of the assumptions underlying some of their indirect methodologies. An alternative hypothesis was suggested: Rather than arsenate incorporation, some scientists hypothesize that arsenate is rather sequestered. Great claims require great proofs which in the minds of these scientists had not been brought forward. In response to the criticism the author decided to submit the strain to two publically available culture collection centers (the American ATCC and the German DSMZ) to allow for their more widespread studies.
 
Literature Cited:


Felisa Wolfe-Simon et. al. "A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus."
Science Express, December 2, 2010, pp 1-9
Link: http://www.sciencemag.org/content/early/2010/12/01/science.1197258.full.pdf
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