Off Topic: Odd bacteria may change definition of life itself


Odd bacteria may change definition of life itself



Scientists say they have found a bacterium that can exist without phosphorus, one of six elements assumed to be necessary for life on Earth.
Scientists say they have found a bacterium that can exist without phosphorus, one of six elements assumed to be necessary for life on Earth.
"We've cracked open the door to what's possible for what life looks like elsewhere in the universe," said Felisa Wolfe-Simon, a NASA astrobiology research fellow with the U.S. Geological Survey who led the study. Findings are reported in today's issue of the journal Science.
Working with colleagues at the U.S. Geological Survey and Arizona State University, Wolfe-Simon uncovered a bacterium in the briny, toxic waters of Mono Lake in California that was able to thrive and grow when the usually toxic element arsenic was substituted for phosphorus.
This bacterium, strain GFAJ-1 of thehalomonadaceae family of Gammaproteobacteria, incorporates arsenic into its genetic structure, according to the report.
The findings, if they hold up, will change the textbooks and the way we think about what constitutes life, said James Elser, a Regents professor of ecology, evolution and environmental science at ASU.
Elser and Wolfe-Simon made their comments in a NASA webcast Thursday.
"Every living thing uses phosphorus to build its DNA," Elser said. "The possibility that it's not true is shocking."
Phosphorus, carbon, hydrogen, nitrogen, oxygen and sulfur were thought to exist in the fats, proteins and DNA of all living things.
Finding an exception to that rule expands the potential habitats in which life might be found outside Earth, said astrobiologist Chris Impey, deputy head of the University of Arizona's Department of Astronomy, who is not connected with the study.
"You can take away what you thought was a critical ingredient, and it doesn't mean life is not there," said Impey.
Impey said the study is a "cautionary tale" for scientists planning space missions in search of life. "They'll only find the life they are looking for," he said. There may be life out there that doesn't need phosphorus - or one or all of the other six elements we think are needed for terrestrial life, Impey said.
Astrobiologists, who combine the expertise of a variety of sciences in the quest to discover how life developed and where it might be found outside our world, have long been interested in extreme habitats as places to find exceptions to the rules we have about what is necessary for life to exist.
They study microbes in caves, organisms that exist in the light-deprived steam vents beneath the ocean or in marooned ecosystems such as Mono Lake, east of the Sierras in California, whose tributaries were diverted in the 1940s to supply water to Los Angeles.
Wolfe-Simon said she thought Mono Lake, where already high arsenic concentrations rose and salt content tripled as its level fell more than 40 feet, might be a good place to look for organisms that might not follow the normal rules for life.
She took samples of Mono Lake sediment and then "selected for any organism that could tolerate an environment she created in a lab - an arsenic feast but starved of phosphorus," said Ariel Anbar, who directed Wolfe-Simon's research at ASU, where the idea was hatched.
Wolfe-Simon initially floated the idea at a 2006 conference on alternative forms of life, hosted by ASU's BEYOND Center, where she remains an adjunct faculty member.
She joined with center director Paul Davies and Anbar, director of ASU's astrobiology program, to propose the theory in a January 2009 paper in the International Journal of Astrobiology.
Anbar, in a telephone interview, said Wolfe-Simon's discovery "rocks the socks of the biological world."
She was a post-doctoral researcher in Anbar's lab when she proposed the experiment, said Anbar, "then she went off to really hunt this thing down." Anbar and Davies are co-authors of the paper, as is ASU's Gwyneth Gordon, who did analysis of arsenic and phosphorus in the samples.
"The big implication," said Anbar, "is that there are the six elements that are important to life and here we find that that assumption may not be quite right."
Steven Benner, of the Foundation for Applied Molecular Evolution, was skeptical of the results at the NASA webcast. He said it was the role of the chemist on the panel to throw a "wet blanket" on the excitement. Benner said the bacterium is certainly interesting, but did not yet merit pronouncement of a new form of life.
"An exceptional result requires exceptional evidence to support it," Benner said.
Anbar said results were tested and retested before the paper was published and he expects follow-up experiments will continue to prove the findings.
It will change the way we think about potential life forms, said Impey.
"I think it's a nice experiment to show that you shouldn't make any strong statement that says 'Life needs X, Y or Z,' " said Impey. "Astronomers can't say life can only exist in places X, Y or Z."
Contact reporter Tom Beal at tbeal@azstarnet.com 

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