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HindustanTimes Thu,21 Aug 2014

NASA claim of arsenic life disproved
PTI
Washington, July 11, 2012
First Published: 16:09 IST(11/7/2012)
Last Updated: 18:19 IST(11/7/2012)
A NASA TV grab shows the space shuttle Endeavour with Earth in the background, after undocking from the International Space Station.

The claim by NASA scientists that they have discovered a new form of bacteria which thrive on arsenic has been disapproved by two new studies, which say the bugs can't substitute arsenic for phosphorus to survive.

Two scientific papers, published in the journal Science, refuted the 2010 NASA finding that bacterium called GFAJ-1 not only tolerates arsenic but actually incorporates the poison into its DNA, swapping out phosphorus.

"Contrary to an original report, the new research clearly shows that the bacterium, GFAJ-1, cannot substitute arsenic for phosphorus to survive," the journal said.

"If true, that finding would have important implications for our understanding of life's basic requirements since all known forms of life on Earth use six elements: oxygen, carbon, hydrogen, nitrogen, phosphorus and sulphur," it said.

If an organism on Earth were found to survive without one of these building blocks, it could mean that life on other planets (as well as our own) is more adaptable than expected. Felisa Wolfe-Simon, who led the NASA study, acknowledged very low levels of phosphate within their study samples; but, they concluded the contamination would've been insufficient to allow GFAJ-1 to grow.

Now, the two separate studies find that Wolfe-Simon's medium did contain enough phosphate contamination to support GFAJ-1's growth, LiveScience reported.

It's just that GFAJ-1, a well-adapted extremophile living in a high-arsenic environment, is thrifty, and is likely capable of scavenging phosphate under harsh conditions,helping to explain why it can grow even when arsenic is present in its cells, the new studies claimed.

Wolfe-Simon and her colleagues discovered the bacteria in desolate Mono Lake in California, finding evidence the extremophiles could munch on arsenic to survive in the absence of phosphorus, an element long established as a critical building block of life.

The finding soon spurred a lively debate, with outside researchers criticising the paper's methods. "The basics, growing the bacteria and purifying the DNA, had a lot of contamination problems," said microbiologist Rosie Redfield of the University of British Columbia, in February. Redfield is the author of one of the newly published Science papers.


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