Why the Arsenic-Eating Microbe is a Huge Deal

"NASA has found a new form of life? Neat. Call me when it's got heat vision, wears blue pajamas, and flies."

So one wisenheimer tweeted in reaction to the official word out of NASA that no, researchers had not made contact with an extra terrestrial. But let's not get blase' in the face of history: the discovery of a microbe that can use arsenic as one of its nutrients is a mind-blowing event.

Maybe the disappointment of some was is understandable given the hype and excitement around NASA's announcement earlier in the week that it planned a Thursday announcement connected to "an astrobiology finding that will impact the search for evidence of extraterrestrial life."

And so it was - even if the day's agenda did not include a walk-on by a google-eyed alien.

For starters, the discovery of an arsenic-eating microbe will surely force some heavy editing of scientific textbooks. The assumption has been that there are six major elements considered essential for life: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. Thursday's announcement replaces that coda with a question mark.

If phosphorus is not necessarily needed as a central component of the energy-carrying molecule in all cells, then what about the others?

"This cracks open the door," said Felisa Wolfe-Simon, whose team found evidence of the weird bacteria on the remote shores of 10 Mile Beach at Mono Lake in California.

Wolfe-Simon and a clutch of scientific colleagues, who assembled at a NASA-sponsored event in Washington Thursday afternoon to discuss the finding, were bubbling over with excitement as they discussed the findings. Whether it strikes the same chord among laymen is still unclear - though it should.

Geobiologist Pamela Conrad pointed out that the microbe in question acts very differently from "life as we knew it" in its ability to substitute arsenic for phosphorous."

To be sure, this dual ability to grow using either element qualifies as a first in the annals of science. Even though this doesn't qualify as a textbook example of a life form from another planet, it will force scientists to recalibrate their assumptions as they search for other forms of life.

Ecologist James Elser of Arizona State University disposed of understatement when he said the discovery basically shakes the heretofore bedrock assumption that organisms cannot grow without needing phosphorous.

"Every living thing uses phosphorus," he said. "To say that it's not true is shocking."

Horta Today, ET Tomorrow?

During the Q&A, one scientist recalled a "Devil in the Dark" "Star Trek" episode from 1967 which featured a silicon-based creature called the Horta. In a similar way, today's announcement challenges science's concepts about the fundamental building blocks of 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, United Kingdom. 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 wasn't a chance discovery.

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 isn't 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.

(The Associated Press contributed to this report)

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