Felisa Wolfe-Simon wades into Mono Lake to gather arsenic loving bacteria. Photo Credit/Henry Bortman
Scientists have identified a surprising form of bacteria that incorporates toxic arsenic rather than traditional phosphorus into the backbone of its DNA, the microscopic genetic material found in the nucleus of cells.
The surprising finding re-defines under what conditions life might thrive, according to scientists who carried out the NASA-funded research.
While long considered an unstable component of DNA in Earth-like environments, arsenic would be a stable part of a DNA chain in a similar microbe on Titan, a moon of Saturn that resembles a primitive Earth. Titan’s extreme cold, temperatures of 290 degrees below zero, would make the arsenic laced DNA quite hardy.
“We found that not only did this microbe cope, but it grew and it thrived,” said Felisa Wolfe-Simon, a NASA astrobiology research fellow at the U. S. Geological Survey who led the study. “We have cracked the open the door to what is possible for life elsewhere in the universe. That is profound to understanding how life has formed and where life is going.”
The findings were based on a hunch that took Wolfe-Simon to Mono Lake, an isolated body of water in California east of the Sierra Mountains and south of Yosemite National Park. Though rich in toxic arsenic, the briny lake is teaming with life and serves as a stopover for migratory birds.
The research team gathered mud from the lake, took it to their labs and added nutrients and more arsenic to see what would happen to the newly discovered microbe, GFAJ-1. The microbe is a member of a common family of bacteria, the Gammaproteobacteria.
The elements carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur are the six basic building blocks of all known forms of life on Earth. In addition to its role in DNA, phosphorus is a central component of the energy-carrying molecule in all cells, adenosine tri phosphate, as well as the phospholipids that form cell membranes.
Arsenic, which is chemically similar to phosphorus, is poisonous for most life on Earth. It disrupts metabolic pathways because chemically it behaves similarly to phosphate, a molecular form of the element.
That makes the findings, which were published Thursday in the journal Science, all the more surprising.
Earlier this week, word of Thursday’s announcement became rich fodder on the Internet, with some bloggers suggesting NASA was prepared to reveal new evidence for extra-terrestrial life.
“The discovery of an extraterrestrial would be an incredible announcement,” acknowledged Mary Voytek, NASA’s director of astrobiology programs. She compared the revelation to a popular science fiction theme, a human encounter with an intelligent form of life based upon the silicon rather than the carbon atom.
“We feel from our perspective and our understanding of biology here on Earth that this is a phenomenal finding,” said Voytek. “This will require some paragraphs in the textbooks to be re-written.”
However, not all experts agree. NASA included a skeptic as part of its presentation.
Steven Benner, a scientist from the Foundation for Applied Molecular Evolution, was troubled by the instability of arsenic in DNA. He questioned the amount of energy and time it would take the arsenic-based DNA chains to rebuild their bonds as they deteriorate in an Earth-like environment.
“If you go to an exotic environment…in our solar system, there are places, and Titan, a moon of Saturn, is one of them, where a very reactive species of arsenate could be very useful,” said Brenner. “Just because they are too unstable to exist in many environments on Earth, doesn’t mean they are too unstable to exist in an environment like Titan.”