Life, but not as we know it

 

Michaela Livingstone


A newly discovered bacterium uses the deadly arsenic to grow and live.


The only organism able to use a different chemical from the accepted fundamental building blocks of life has been found living in a lake in California, substituting phosphorus for the usually poisonous element arsenic, opening up questions on what other forms of life might be possible in the universe.


Until now, all life on Earth has been found to use the same basic building blocks for life, the elements carbon, hydrogen, oxygen, nitrogen, phosphorus and sulphur. These elements make up the various cellular parts and machinery from DNA to proteins and lipids.


The bacterial strain, named the not-so-exotic GFAJ-1, was isolated from mud samples collected from the shores of the briny Mono Lake in California, known to have high levels of arsenic, by NASA researcher Felisa Wolfe-Simon and was reported in a research article in this week’s issue of the journal Science.

Phosphorus is contained in a phosphate form (phosphorus and oxygen) in the backbone of DNA and RNA, as well as energy-carrying molecules such as ATP. There had been suggestions that arsenic in the form of arsenate could be used by life as it is chemically similar to phosphate, which is why it is usually deadly.


The bacterium was shown to have arsenate incorporated in to its DNA and other cellular parts when grown in media lacking phosphorus but containing a relatively high level of arsenic. The organism was however still able to grow faster in the presence of phosphorus.


Some researchers have hailed this as evidence that it is possible for life elsewhere in the universe to use different chemicals as their building blocks, opening up many possibilities for extraterrestrial environments where life could thrive, where before it was thought impossible. It suggests that anything is possible and that alien life may look very different from what we have assumed, if we ever come face to face with it.


Others say it opens up questions as to how, and how many times, life may have evolved here on Earth speculating that life may have evolved in harsh environments with high levels of arsenic such as volcanic vents on sea beds before later incorporating phosphorus.


Clara Chan, a geomicrobiologist from the University of Delaware, Newark was reported by the journal Science as saying that the strongly held belief is that the chemistry of life is so specific that any changes would not be tolerated, “The implication of this work is that life can be quite different from what we know.”


Other scientists are less convinced by the data, withholding belief that the organism really is able to use arsenate in place of phosphate until more data is produced to show that the arsenate isn’t simply being stored in the bacterium.


GFAJ-1 at least shows that is possible for life to exist in the absence of phosphorus. Wolfe-Simon hopes now to find bacteria growing naturally in high-arsenic but low phosphate-containing environments to find proof of life that depends on arsenic.

 

Find the original research article here:

http://www.sciencemag.org/content/early/2010/12/01/science.1197258