Arsenic Consuming Microbes: Life Not As We Know It.

I was just about to knock off one of the many RSS feeds I had a massive backlog on when I noticed an article about NASA making a pre-announcement about a press conference they were going to have today. Usually this stuff isn’t front page news but this one had just the right combination of words to send us space nuts (and a good chunk of regular people too) into wild speculation about what NASA might have found. Even more interesting was the fact that one of my friends sent me a rabid SMS directing me to the same article. Something told me that whilst this wouldn’t be your run of the mill NASA press conference there was something big on the horizon, leaving my mind to buzz around all the possibilities.

NASA was not one to disappoint on this occasion.

Researchers at NASA’s Astrobiology Institute have discovered a microbe, native to California’s Mono Lake (a highly inhospitable place), that can survive and thrive by replacing one of the essential building blocks of life with an element that’s highly toxic: arsenic. The bacteria, known as GFAJ-1, was known to be arsenic resistant but researchers took it one step further by depriving the microbes of all phosphorus and flooding their environment with arsenic. The result was that not only did the bacteria survive they thrived, continuing to multiply as if nothing had changed in their environment. Further analysis of the bacteria showed that they had incorporated the arsenic into their DNA where the phosphorus should have been. This throws so many things into question and will change the way we search for alien life out in the universe.

The space and science news sites are abuzz with the implications of the discovery and what it means for the future of astrobiology. The news was so big that it even made the morning news here in Australia something that even the shuttle launches struggle to accomplish. Whilst this announcement isn’t as fantastical as some had hoped for (first contact being amongst them) we’re still at a turning point in our understanding about how life formed here on earth and how it can form elsewhere in the universe.

The discovery is interesting as prior to finding these microbes all life on earth has needed to use 6 building blocks in order to survive: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. Arsenic is just below phosphorus on the periodic table so it shares quite a lot of properties with it and that similarity means it can be substituted into some biological reactions. However arsenic is far more reactive than phosphorous and this means that it is highly toxic to almost every life form on the planet. This bacteria however seems to have developed the ability to use arsenic when it is in a phosphorus poor environment and even has the ability to switch back to phosphorous should it become plentiful again (it actually seems to prefer it).

As with any big discovery this one is not without its critics. Steven Benner, a chemist from the Foundation for Applied Molecular Evolution, makes the point that whilst these bacteria were phosphorus starved there were traces of it available. Enough possibly to sustain these bacteria in the arsenic rich environment. Additionally should these bacteria be incorporating arsenic into their DNA it would be in the form of a arsenate, an ester of arsenic. Such a compound would hydrolyse in water making such arsenate based DNA unstable. He hypothesises that the arsenic is being used in some other fashion, possibly in a way that we do not yet understand. The research is of course continuing and will address these concerns.

We’ve known for a long time that life can develop in places we’d long thought it was impossible to do so but this discovery is something on a whole new level. Showing that a life form, even if it’s a simple one, can replace one of the fundamental building blocks of life with something thought to be toxic means we have to rethink the way in which we look for life here and out in the vastness of space. The prospect of finding life on other planets and moons here in our own solar system just got more possible as our understanding of how life can thrive undergoes a radical paradigm shift. I can’t wait to see how this develops and I’m sure this isn’t the only bacteria out there capable of feats like these. Who knows what kind of alien life we’ll find right here in our own little rock called earth.

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