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New bacteria tests the limits of life on Earth and beyond

Text by News Wires

Latest update : 2010-12-03

NASA's discovery of a bacteria that can use arsenic as a nutrient shows that life can exist beyond the confines of what is normally considered possible, according to a report in Science magazine. The bacteria was discovered in California's Mono Lake.

AP - Bacteria that thrive on arsenic have been scooped from a California lake, a discovery that redefines the building blocks of life and offers new hope in the search for other organisms on Earth and beyond.
Not only do the bacteria survive, they grow by swapping phosphorus for arsenic in their DNA and cell membranes, said the study funded by the US space agency NASA and published Thursday in the journal Science.
The findings add a new dimension to what biologists consider the necessary elements for life, currently viewed as six elements: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur.
"What we've found is a microbe doing something new -- building parts of itself out of arsenic," said scientist Felisa Wolfe-Simon, a fellow in NASA's astrobiology program who made the groundbreaking discovery at Mono Lake in eastern California.
"There's an organism on Earth doing something different," said Wolfe-Simon. "We've cracked open the door to what's possible for life elsewhere in the universe. And that's profound."
Ariel Anbar, a co-author of the study, explained how Wolfe-Simon was able to get the bacteria known as strain GFAJ-1 of the Halomonadaceae family of Gamoproteobacteria to grow under extreme toxic conditions in the lab.
"She takes this sediment, puts it in a bottle essentially where there is lots of arsenic and very little phosphorus, and she does it over and over so only organisms that are going to be happy in that environment survive," said Anbar.
"The organism came from nature," said Anbar, a scientist at Arizona State University's School of Earth and Space Exploration. "It is a known bacteria. It is not a brand new bug but nobody realized it could do this," he said.
Scientists have known for some time that some microbes can use arsenic for energy, much like humans do with oxygen or food.
"The way I like to put it is they smoke it but they don't inhale it," said Paul Davies, a co-author of the paper and British-born cosmologist at Arizona State University.
"So the big question we all wanted to know was where has the arsenic gone? Is the arsenic really in their innards?
"Eventually, bit by bit, the evidence accumulated that indeed the arsenic was in the DNA, the proteins, the lipid membranes and the metabolites, so it was everywhere where it is important."
A few years ago, Wolfe-Simon, Anbar and Davies began discussing the idea that different life forms could exist on Earth but by biological rules unlike ours, a notion known informally by scientists as "weird life."
The trio published in 2009 their hypothesis that arsenic, which is directly below phosphorus on the periodic table, could substitute for phosphorus in Earth life forms.
"We conjectured that maybe life started via the arsenic route and phosphorus was the later adaptation," said Davies, noting that they still are not sure which came first, or if this bacteria could be "like a living fossil, a hangover from an earlier arsenic epoch."
But the discovery has made him think about all the forms of life out there that scientists may have missed.
"This is going to open up a whole new line of inquiry. First of all this can't be the only arsenic organism on the planet, there is going to a be lot more, so this is a whole new domain of microbiology that it represents," said Davies.
"Who knows what else is out there if we take a harder look?"
The findings, leaked early in a vague but intriguing announcement by NASA that mentioned "extraterrestrial life," lit up the blogosphere and stunned many scientists.
Arizona State University professor James Elser said he has spent years telling students that phosphorus was a necessary part of DNA.
"The idea that I am sitting here today discussing the idea that this is not true is shocking," said Elser, a panelist at a NASA press conference on the discovery.
Caleb Scharf, a Columbia University astrobiologist, told The New York Times he was amazed.
"It's like if you or I morphed into fully functioning cyborgs after being thrown into a room of electronic scrap with nothing to eat," he said.
NASA has conducted numerous probes at eastern California's Mono Lake, an unusually salty body of water with high arsenic and mineral levels, as it is likely to reflect conditions under which early life evolved on Earth, or perhaps Mars.
"Sometimes you think something is not going to work, but then you go looking for it and sometimes you may find it," said Anbar.
"And then you realize, oh, I didn't understand things quite as well as I thought I did before. And that happens all the time in science. That's part of what makes it fun."AP - The discovery of a strange bacteria that can use arsenic as one of its nutrients widens the scope for finding new forms of life on Earth and possibly beyond.

While researchers discovered the unusual bacteria here on Earth, they say it shows that life has possibilities beyond the major elements that have been considered essential.
“This organism has dual capability. It can grow with either phosphorous or arsenic. That makes it very peculiar, though it falls short of being some form of truly ‘alien’ life,” commented Paul C. W. Davies of Arizona State University, a co-author of the report appearing in Thursday’s online edition of the journal Science.
Six major elements have long been considered essential for life -- carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur.
But the researchers found that the bacteria, discovered in Mono Lake, California, is able to continue to grow after substituting arsenic for phosphorous.
“It makes you wonder what else is possible,” said Ariel D. Anbar of Arizona State University, a co-author of the report.
The find is important in the search for life beyond Earth because researchers need to be able to recognize life, to know what life looks like, Anbar said.
The study focuses on a microbe found on Earth. However, the announcement of a news conference to discuss it, which did not disclose details of the find, generated widespread speculation on the Internet that the report would disclose the discovery of extraterrestrial life.
The discovery “does show that in other planetary environments organisms might be able to use other elements to drive biochemistry and that the ‘standard’ set of elements we think are absolutely necessary for life might not be so fixed,” commented Charles Cockell, professor at the Planetary and Space Sciences Research Institute, Open University, in Milton Keynes, Britain. Cockell was not part of the research team.
“This work is novel because it shows the substitution of one element for another in fundamental biochemistry and biochemical structure,” added Cockell.
It was not a chance discovery. Felisa Wolfe-Simon of NASA’s Astrobiology Institute, who led the study, targeted Mono Lake because it has high arsenic levels. Arsenic and phosphorous are chemically similar, so she speculated that a microbe exposed to both might be able to substitute one for the other.
“Arsenic is toxic mainly because its chemical behavior is so similar to that of phosphorus. As a result, organisms have a hard time telling these elements apart. But arsenic is different enough that it doesn’t work as well as phosphorus, so it gets in there and sort of gums up the works of our biochemical machinery,” explained Anbar.
The researchers collected the bacteria known as GFAJ-1 and exposed it to increasing concentrations of arsenic, which it was able to adapt to and grow.
The microbe does grow better on phosphorous, but showing that it can live with arsenic instead raises the possibility that a life form using arsenic could occur naturally, either elsewhere on Earth or on another planet or moon where arsenic is more common.
Jamie S. Foster, an assistant professor of microbiology at the University of Florida, said the idea that arsenic could be substituted for phosphorous is not new, but there has never been example where it was shown to work.
Arsenic was more common in the early times on Earth, she said, so researchers have speculated that early life forms might have used it.
“It does suggest that that there could be other ways to form life, not just how life formed on early Earth,” said Foster, who was not part of Wolfe-Simon’s research team.
The research was supported by NASA, the Department of Energy and the National Institutes of Health.


Date created : 2010-12-02