Arsenic Based DNA: Science Fact or Fiction?
On December 2nd 2010 NASA held a press conference to discuss the breaking news that NASA funded researchers had discovered the first living organism on the planet able to build DNA out of something other than phosphorus, which is normally the ‘backbone’ of DNA. The element was arsenic, the organism a microbe known as GFAJ-1, a strain of the Halomonadaceae bacteria. This was heralded by NASA and the attendant media as a breakthrough in the search for extraterrestrial life and a reason to rewrite biology textbooks.
Felisa Wolfe-Simon collected the bacteria from Mono Lake in California. With no incoming fresh water tributaries the lake is very alkaline and has high levels of salt and arsenic making it a potential habitat for extremophile organisms that thrive in harsh environments. Back in the lab Wolfe-Simon and her colleagues grew the bacteria in a virtually phosphate free medium containing high levels of arsenic and then conducted tests to identify how the molecular processes of the bacteria reacted to the conditions. The results were published online by the journal Science along with a commentary by a journalist for Science at the same time as NASA was holding its press conference.
Surprisingly the bacteria that were placed in near phosphate free conditions with high levels of arsenic survived and even showed evidence of colony growth. This suggested that GFAJ-1 was using arsenic instead of phosphate to form important cellular molecules such as adenosine triphosphate, the energy source for cells, proteins, and DNA. The tests that they ran seemed to confirm this fact and provided evidence suggesting that indeed arsenic was being built into cellular macromolecules in place of phosphorus. The most notable of these observations was the fact that the bacteria were producing arsenic based DNA, something which is completely unique on Earth and opens up the possibility that life on other planets could be arsenic based as opposed to phosphorus based. It was this result that so completely captured the attention of the media.
Two days after the research appeared in Science, and NASA told the world about this new form of life, Dr. Rosie Redfield of the University of British Columbia wrote a post on her research blog regarding her concerns about the accuracy of the claims being made. From her analysis of the research report she suggests that the bacteria are not incorporating arsenic into their DNA as there was just enough phosphorus contamination in the media to support the slowly growing cells. In addition the techniques used to suggest that arsenic had been incorporated into the bacterial DNA did not directly prove this idea and the results could be due simply to arsenic being present in the cell in vacuoles or dissolved in the intracellular fluid without being incorporated into anything. Similar views were expressed by researchers interviewed by Science for the commentary on the report and by many others across the internet in the days following publication. The backlash against the research and NASA’s claims turned into quite a storm which reached both the scientific and mainstream press.
In the end the hype surrounding the announcement raises issues about the media and people’s relationship with science and obscures what is quite an interesting piece of research. In the artificial conditions of a lab GFAJ-1 is able to survive in a very toxic environment surrounded by high levels of arsenic. The bacteria may or may not be using the arsenic to help them survive but at least they are adapted to be able to cope, a fact which could shed light on how life developed on Earth. Unfortunately it may not be exactly what was claimed by some but time, further analysis and independent repetition by other researchers may show if this discovery was as important as it seemed on 2nd December.
About the author: Ruth Warre is scientific writer and editor based in Toronto. Her writing has covered many biomedical topics from Parkinson’s disease to aging. She has a PhD in Neuroscience and her research work has been published in several scientific journals.