Sunday, December 5, 2010

Arsenic Bacteria

Well I guess my science education hasn't been as good as I thought; last Thursday it was reviled that a bacteria had been evolved in a lab that swaps arsenic for phosphorus. The media is hailing the as rewriting the building blocks of life as we know it. I feel like I should have learned how essential the building blocks of life are, unless it turns out they're not really that essential.

First off, on Wednesday morning I read that NASA was going to have a press release about alien life. So I was hoping for so news from deep space, not from earth. This bacteria not extraterrestrial at all!

The building blocks of life are considered to be oxygen, carbon, hydrogen, nitrogen, sulfur, and phosphorus. My question lies with anaerobic organisms. What role does oxygen play for them? Bacteria have been discovered that use arsenic instead of oxygen (though this is a very different process than replacing phosphorus with arsenic; phosphorus is a key component in the structure of DNA). So is oxygen considered a building block for anaerobic organisms? My intro-level biology course has me believing it isn't. Also, a google search of oxygen and anaerobic bacteria turns up mostly results of anaerobic bacteria not needing oxygen at all (but little is mentioned on if and how oxygen in any of its forms plays a role in their structure).

To anaerobes, oxygen gas can be lethal. However, oxygen is also a key part of water (H20),  and anaerobic organisms can live in it. The bacteria were originally found in a lake before being artificially introduced into a phosphorus free environment and forced to die or survive on arsenic. The individual bacteria grew larger, and more hollow. I find the increase in size unsurprising, since arsenic has a larger radius than phosphorus.

Let's consult our periodic tables. Phosphorus and arsenic are Group V elements (as is nitrogen), so they are similar in structure, but arsenic is bigger than nitrogen or phosphorus. Interestingly all the building blocks are non-metals while arsenic is a metalloid, that's about the most interesting thing that I've gathered from this.

Come on NASA, this is not alien life. This is some bacteria artificially induced into using arsenic. Bring me some silicon based lifeforms and then we'll talk.

We are too narrow in our idea of what life can be. Research in the past has been aimed at looking for environments similar to earth (hence looking for those building blocks) on other planets. But should we really be expecting extraterrestrial life to have evolved along the same path that life here has? Sure, all Earth life is built on DNA, but that isn't the universal code it's portrayed as (it's not even totally consistent in all discovered life). Can we expand our imaginations beyond looking for DNA based organisms? If our origin of life turns out to be earth based, the chances of other planets having an identical path of evolution is infinitely small. With research like this we're already showing that life isn't as strictly controlled as once believed. Will we even recognize extraterrestrial life if/when we find it? My expectation is that on the minute chance that any alien life is ever discovered in my lifetime (and I'm giving myself at about 60 more years) that it won't look like anything we know or could have imagined possible on earth.

Links to articles on arsenic swapping bacteria

R&D Magazine
NYTimes
The Daily Telegraph (on life before an oxygenated atmosphere)

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