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December 8, NASA: Life with arsenic December 7, Last week, in a much publicized news conference, NASA announced the discovery of a bacterium that can use arsenic instead of phosphorus.
The news media covered it with a flourish -- and produced much nonsense. The paper was posted at the Science magazine web site, so we can look at what was really shown.
Whatever the hype that the news media added, it is an interesting -- but incomplete -- story. The figure at left shows a key experiment; this is Figure 1B of the paper.
The graph shows the growth of the bacteria under different conditions. Number of cells on the y-axis log scale ; time on the x-axis. The three conditions are, from the top: Importantly, if there is no addition, the bacteria grow very little, if at all lower curve. Then, arsenic in the form of arsenate does indeed stimulate growth middle curve.
So does phosphate; in fact, it is better upper curve. The above experiment along with other measurements does seem to establish the basic point: But now let's look at some of the limitations of the story -- as we have it so far.
First, the bug prefers P to As: You can see this in the graph above. They explicitly do not claim that the bug requires or prefers As, merely that it can use it. Second and more importantly, the growth medium with no added P contains a trace level of P.
This probably comes from low levels of P contaminating other chemicals they use. It's not enough to support growth alone lower curve in the graphbut it does mean that when the bugs are growing on As, they also have a small amount of P available.
In fact, analysis of the bacteria grown on As shows a weight ratio of about 7 As: On a mole basis, the ratio would be about half that. Thus there still is considerable P in the bacteria. They cannot claim a total replacement of As for P. The paper recognizes this limitation, but some of the news coverage does not.
This may be interesting, too. So, where is the As in the cell? This becomes particularly important since the replacement is incomplete. And this is where the paper gets rather weak.
They hand-wave that it is everywhere, but there is little specific information. Where did this bacterium come from? It was isolated from Mono Lake -- a highly alkaline lake in the Sierras of eastern Californiawith a high As level.
Thus it is likely that the starting bug was quite resistant to As. All the reported work was done under lab conditions. There has been an opportunity for both physiological and genetic adaptation. Thus we do not know whether the bug uses As in nature.
This does not minimize the importance of the work as a proof of principle.MCAS Cherry Point MILITARY RELOCATION Welcome to Craven County Home of Marine Corps Air Station Cherry Point MARCOA Media, LLC Black Mountain Road San Diego. Phoenix HRM Final Exam Answers (Fall ) 1. The Age Discrimination in Employment Act of states that: 2.
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