Arsenic(?) Bacteria

Recently, a strain of bacteria was identified in Mono Lake, CA that could supposedly use arsenic instead of phosphorous.  The media immediately jumped on this, reporting all sorts of miraculous sounding things.  I start this off with a list of things that the media misreported or misinterpreted:

1. The discovery wasn't an accident. It has been previously theorized that arsenic could be used. To test it, they found an environment with a lot of naturally occurring arsenic, scooped some stuff out, and looked to see if anything could grow on an arsenic diet.
2. Arsenic and phosphorous behave very similarly chemically. Arsenic compounds just tend to be less stable than the phosphorous ones.
3. It grows much faster with phosphorous than with arsenic. In other words, it prefers phosphorous.
4. It does not appear to be able to differentiate between arsenic and phosphorous.
5. It appears to create an internal microenvironment in which arsenic just happens to be more stable than it usually is. This microenvironment is characteristic of this bacterial species, including strains that are not known use arsenic. In other words, the arsenic usage ability is tagging along with something else it needs, so it's not all that different.

Assuming the bacteria really do use arsenic, I'm just not too impressed.  A quick glance at Wikipedia shows that Mono Lake formed about 760,000 years ago.  The lake has no outlet to the ocean, which has allowed dissolved materials to remain trapped in the lake.  This normally refers to salts and alkaline compounds, but the same goes for arsenic.  This bacterium did not suddenly grow accustomed to arsenic over a course of mere decades due to human pollution, but rather it was gradually exposed to slowly increasing levels of arsenic over a long period of time.  I'd be impressed if it were only such a short period, but given the amount of time this adaptation is not unreasonable. 

Again, this is all assuming that the bacteria really do use arsenic.  Quite frankly, the evidence is not too convincing, which has been pointed out elsewhere.  I don't have a deep background in chemistry, but I am familiar with a few of the techniques that were used in determining if the bacteria use arsenic.  One of these techniques is a phenol-chloroform extraction, which is commonly used to separate out different parts of cells based on polarity characteristics.  Portions with certain characteristics congregate into one of three portions of a solution.  It looks much like a mixture of oil and vinegar that has been allowed to sit for some time; there will be a distinct separation of the two.

After performing this separation on cells, they determined how much arsenic was in each portion (well, sort of.  More on this below).  Table 2 of the paper confidently says "Chloroform (lipids)", and says how much arsenic is in this portion.  However, many more things than lipids can dissolve in the chloroform layer.  Additionally, some of the numbers have extremely high standard errors, as with 1.5 +- 0.8 for the aforementioned value.  The use of this simple technique along with such high error suggests to me that the paper was rushed out the door, and further examination could reveal otherwise.

There is an additional problem with the phenol/chloroform extraction.  There is nothing to compare these values to.  These values measure the percentage of arsenic found in the given portion, not the actual amount.  Being that my own body contains trace amounts of arsenic, my own cells could very well have the same percentages.  In fact, being that both my own cells and these bacterial cells cannot differentiate between arsenic and phosphorous, they likely do have similar values!  It would be nice to have these values compared to some sort of control to see if there really is anything special going on.  There are some bacteria which can live in arsenic-contaminated environments by actively pumping out arsenic or otherwise detoxifying it, which would have made great candidates for controls.  After all, with such behavior one would expect different percentages for arsenic.

In conclusion, I'm just not impressed with either the bacteria or the paper's methods.  I can understand the need to publish a discovery like this ASAP, but I fear that someone jumped the gun before we can say for sure.  If these bacteria are not actually using arsenic but are merely very tolerant of it, then this could become a major embarrassment.  For such dramatic findings I would expect dramatically conclusive data, and I'm just not seeing it.