Arsenic and Old Space: The Possibilities of Life

Posted by: Mike Pallante on January 17, 2011 at 10:59AM
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On December 2nd 2010 NASA held a conference headed by geomicrobiologist Felisa Wolf-Simon on a discovery which may change how we search for extra terrestrial life. The panel revealed findings about a microbe, GFAJ-1, found in Mono Lake in Eastern California which Wolf-Simon described as, “life, but not as we know it.” The NASA funded research team found that GFAJ-1, under laboratory conditions, substituted Arsenic, a poison, for phosphorus, in life processes.

Life As We Know It, Alien or Otherwise

Biologists consider a handful of elements Carbon, Hydrogen, Nitrogen, Oxygen, Sulfur and Phosphorus necessary for life; however, Felisa Wolf-Simon describes herself as, “...interested in the exceptions to the rules.” To Wolf-Simon the most obvious exception was Arsenic. Arsenic and Phosphorus have a similar “atomic radius”, or size, and share certain other chemical properties. In truth these similarities are what make Arsenic such a deadly poison. Cells can't tell the difference between Arsenic and Phosphorus and will attempt to use Arsenic in chemical bonds. Unfortunately, as Arsenic decays quickly, the bonds formed by Arsenic fall apart resulting in death.

Wolf-Simons's research team began their search for an exception to the rule in Mono Lake, a curious body of water in Eastern California. Mono Lake's salt content is three times higher than sea water and the lake contains high levels of Arsenic. As inhospitable as any space environment, Mono Lake supports bacterial life.

Bacteria from Mono Lake was put in laboratory controlled conditions with startling results. Wolf-Simon's team provided everything needed for life except Phosphorus. Instead of Phosphorus the team provided GFAJ-1 with an excess of Arsenic. One would expect the bacterium to die like a human breathing CO₂ instead of oxygen. However, the microbe not only grew but thrived. When measuring the total Arsenic content the team found Arsenic in the bacterium's DNA. Isolating the DNA, the team found Arsenic wasn't simply “stuck in there” but performing functions analogous to Phosphorus.

Phosphorus is the “backbone” of our DNA, holding the double helix structure together. Without Phosphorus our DNA would simply drift about in the cell, never reproducing and incapable of directing cell functions. That the microbe could substitute a fundamental element like Phosphorus with a roughly similar poison like Arsenic flies in the face of everything we know about biology.

GFAJ-1: The Remarkable Microbe

GFAJ-1 substituting Arsenic for Phosphorus changes how we will define life in the future. This discovery, “Cracks open the doors for what we might find in the universe.” according to Wolf-Simon. The real importance has little to do with Arsenic or Phosphorus, the specific elements are incidental. GFAJ-1's behavior now allows us to ask, “What else might we find? What else should we look for?”

Chemist Dr. Stephen Benner contributed on the exceptional results of the experiment. Arsenate is a bad chemical link, a poison. A biosystem might either evolve knowing better than to try and use arsenate or it might adapt to use arsenate. The latter of these was considered impossible until Wolf-Simon's experiments. Benner paraphrased Caral Sagan in his praise for Wolf-Simon's team, saying, “Science begins when you distrust the experts... [this is] An exceptional claim that is against known chemical properties.”

The weakness of Arsenic based chemical bonds is a weakness at room temperature. Arsenics half life decay in average temperatures causes it to break down too quickly to sustain life processes. Wolf-Simon's experiments, however, were done in low temperature water. At lower temperatures, like those on Saturn's moon Titan for example, the half life decay slows substantially. This experiment demonstrates ways life might have adapted in space which differ from our previous expectations.

The new question, Benner stated, is, “What is life and where might we find it?”
As a planetary Scientist, panelist Dr. Pam Conrad thinks about predicting habitability of an environment off earth by looking at Earth environments. In the light of Wolf-Simon's GFAJ-1 discovery, Dr. Conrad has had to change what metrics she uses in determining habitability. Until now, an environment without Phosphorus, or any other essential element, would have seemed to be clearly uninhabitable to Dr. Conrad. She's not considering or looking for Arsenic in space, rather, she is expanding her view of “habitable” space. Wolf-Simon contributed, “we can [now] experimentally test and show evidence of what is possible.”

The Future of Astrobiology

Wolf-Simon, early in her career, plans future experiments to determine what substitutions are possible and better understand the time frame in which these substitutions occur. Wolf-Simon's work will change the way we look for life in space missions by extending our concept of what environments can sustain life. Certain chemical environments we previously didn't consider habitable may now get a second look. Also, Wolf-Simon's work gives us more tools to examine past life and what may have occurred in the chemical biology of a dead planet or even here on Earth. Future experiments will focus on other types of metabolism, looking at other ways a cell can function beyond substitution of basic elements.

The more we know about how life can survive on Earth the more we can guess at what type of life we may find in space. Wolf-Simon's work is a breakthrough in an understanding of life, Earth and ourselves.