New Bacteria Widens Search For Extraterrestrial Life

A new arsenic-munching bacteria changes scientists views about life on other planets.
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arsenic-munching bacteria
Carrie Arnold, Contributor
WASHINGTON (ISNS) -- A species of bacteria found in California might be able to live like life from another planet. It can nosh on arsenic as if the poison is cheese and crackers.
 
Arsenic is a notorious poison that has featured prominently in mystery novels and plays like "Arsenic and Old Lace." Yet a new study shows that this bacterium can not only tolerate the metallic toxin, it can harmlessly incorporate arsenic into its DNA and proteins.
 
"It's a very exciting and novel study," said biochemist Barry Rosen of Florida International University in Miami who was not involved in the study. "No other organism that has been identified can do this." 
 
Plenty of other bacteria can turn arsenic into harmless chemicals, Rosen said, but this is the first microbe that actually incorporates arsenic into its biomolecules.
 
All life -- from microbes to mammals to what one day may be found on Mars -- needs six elements: carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. Without these elements, biologists believe, life cannot exist. 
 
Yet arsenic is chemically very closely related to phosphorus. So closely related that some astrobiologists -- scientists who study the origin and evolution of life in the universe -- have wondered whether some organisms could use arsenic in place of phosphorus for their biochemical reactions. 
 
The bacteria living in the briny, arsenic-laden depths of Mono Lake in eastern California had clearly evolved to tolerate arsenic, but the team of scientists led by Felisa Wolfe-Simon of the NASA Astrobiology Institute in Menlo Park, California, went one step further. Because arsenic is toxic to humans precisely because our bodies use it as a chemical stand-in for phosphorus, Wolfe-Simon argued that some organisms might be able to adapt to this substitution.
 
Their research, published online today in Science, introduced the world to a type of salt-loving Halomonadaceae bacteria named GFAJ-1 that can use arsenic just as it would phosphorus, with no apparent ill effects. 
 
Wolfe-Simon and colleagues took mud samples from the bottom of Mono Lake and attempted to grow the bacteria in a phosphorus-free environment. Without the ability to form phosphates, no organisms should have grown. But Wolfe-Simon found that GFAJ-1 did in fact grow in the phosphorus-free media.
 
"To be honest, I thought I messed up," Wolfe-Simon said. Repeated experiments showed Wolfe-Simon that she hadn't made a mistake. The bacteria really were growing without phosphorus.
 
Wolfe-Simon's initial results indicated that GFAJ-1 didn't require arsenic for growth -- it actually grew 1.6 times faster when it could use phosphorus instead of arsenic -- but it also didn't require phosphorus. 
 
The researchers next grew GFAJ-1 in radioactive arsenic to see if it was actually using arsenic in place of phosphorus. In normal cells, phosphate groups are attached to proteins to turn them on or off, which affects the cell's metabolism. Fat molecules with phosphate groups form the cell membrane, and the backbone of the DNA molecule is made out of sugars and phosphates.
 
After GFAJ-1 had time to incorporate the radioactive arsenic, Wolfe-Simon isolated and separated the bacteria into proteins, lipids, and nucleic acids. The researchers found radiation in each of the three fractions, indicating that GFAJ-1 was using arsenic in its biomolecules.
 
According to Rosen, more work still needs to be done to show that arsenic was actually used in place of phosphorus.
 
"They haven't demonstrated that any specific molecule has arsenic in it, and if it does have arsenic in it, is it still active and functional," Rosen said. "It has a lot of implications for extraterrestrial life that uses a different kind of chemistry than what we have on Earth."
 
Astrobiologists typically look for signs of life on other planets by looking for chemical traces of the six elements required for life. These findings may mean scientists need to broaden their search for chemical signatures of life. Although more work needs to be done to verify that arsenic was used in place of phosphorus, both Rosen and Wolfe-Simon said that the implications are huge.
 
"[This study] is about changing the way we think about science and changing the way we think about life," Wolfe-Simon said. "If we know so little about life here on Earth, how are we going to find it elsewhere?"
 
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