The discovery of bacteria that grows using deadly arsenic as fuel instead of phosphorus, a chemical building block of most earth organisms, may point seekers of extraterrestrial life in a new direction.
The bacteria, from Mono Lake in California, was grown in lab dishes where phosphate was slowly replaced with arsenic, which is poison for most creatures, until the bacteria began to thrive on arsenic alone, according to a study published online by the journal Science. Mono Lake, located at the edge of the Sierra Mountains, is a 760,000-year-old salt lake with no fish.
All other known life requires phosphorus, according to research cited by the paper. The discovery of arsenic-eating bacteria may give scientists searching for extraterrestrial life a new sign to follow, said Steven Benner, a distinguished fellow of the Westheimer Institute at the Foundation for Applied Molecular Evolution in Gainesville, Florida.
“We’ve cracked open the door for what’s possible,” said the study’s lead author, Felisa Wolfe-Simon, in a news conference today. “This will inform us about life on our own planet, and will help inform us of life -- we will find it one day -- elsewhere in the universe.”
The elements currently thought to be essential for life are carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur, according to the paper.
“We’re going to have to look at a microbe and decide whether it is life or not,” Benner said in a telephone interview. Right now, one of the things to look for is phosphorus, and if today’s finding is confirmed, then a probe to look for arsenic may also hint at life, said Benner, who was not a study author.
Mono Lake, from which the arsenic-eating bacteria were culled, is salty, alkaline and contains heavy arsenic deposits, according to the paper. Scientists cultured the bacteria in the lab, slowly switching its “feed” into arsenic. Using radio- tracers, the team tracked the uptake of the arsenic.
“This result is delightful because I have to expand my notions” of what environments might allow life, said Pamela Conrad, an astrobiologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This opens our perspective to understand what else might be tolerated or essential that we presently haven’t thought of.”
The research indicates that arsenic even replaced phosphate in the bacteria’s genetic code, a strange finding that will need replication, said Benner. Arsenic in the DNA isn’t compatible with other things chemists currently know about the poison, he said.
“It’s not obviously wrong, it’s perplexing,” said Benner. “If this is true, there’s something we fundamentally don’t understand on the chemistry side.”
Phosphate helps provide energy to cells, and powers many functions in living creatures. Arsenic, which is directly below phosphorus on the periodic table, does many of the same things less well, and is poisonous to most living things for that reason, according to a press release from Arizona State University.
Wolf-Simon started the research while a postdoctoral scientist at the Arizona university and is now at the NASA Astrobiology Institute and the U.S. Geological Survey in Menlo Park, California.
The study was funded in part by the National Aeronautics and Space Administration’s astrobiology program.
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