A lifeform built from poison?
On December 2, 2010, NASA announced a discovery from the arsenic mud of Mono Lake. A team led by NASA astrobiology fellow Felisa Wolfe-Simon reported they had found a bacterium that did something previously thought impossible. The microbe, a strain of Halomonadaceae named GFAJ-1, appeared to be able to substitute the toxic element arsenic for phosphorus in its most essential molecules, including its DNA.
All known life on Earth is built from six essential elements: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. Phosphorus is the "P" in the ATP that powers our cells and forms the structural backbone of DNA. Arsenic sits directly below phosphorus on the periodic table, giving it a similar chemical structure, which is also why it is typically poisonous to living cells. The claim that GFAJ-1 could use arsenic in place of phosphorus suggested a second type of life on Earth, expanding the fundamental requirements for what life is. The findings, published in the journal Science, had implications for the search for extraterrestrial life, suggesting organisms could exist on worlds with very different chemistry from our own.
Science corrects itself
The extraordinary claim was met with immediate and intense skepticism from the scientific community. Microbiologists and biochemists raised concerns about the methods used in the original study. Critics, including microbiologist Rosie Redfield, argued that the researchers had not sufficiently purified the DNA samples and that trace amounts of phosphate contamination in the lab experiments could account for the bacteria's survival. Chemists also pointed out that any DNA built with an arsenate backbone would be incredibly unstable in water.
In 2012, two independent research groups published papers in Science that refuted the original findings. After successfully cultivating the GFAJ-1 strain, they found no evidence of arsenic being incorporated into its DNA. Their research showed that GFAJ-1 is a highly arsenic-resistant organism, but it remains dependent on phosphorus for survival. It is exceptionally good at scavenging any tiny amount of phosphate from its environment, which is what allowed it to grow in the phosphate-starved, arsenic-heavy conditions of the lab. The bacterium does not represent a new form of life. After years of debate, the original 2010 paper was officially retracted by Science in 2025. The story of GFAJ-1 is now seen as an example of the scientific process in action: a provocative hypothesis is proposed, rigorously tested by peers, and ultimately corrected.