Arsenic microbe in Mono Lake may reshape hunt for extraterrestrial life

The dotty aunts in "Arsenic and Old Lace" may finally have met their match.

A microbe that thrives in the muck of eastern California's Mono Lake is able to use arsenic, which is poisonous to a wide range of creatures, as one of a half dozen fundamental building blocks in biologically critical molecules such as proteins and DNA.

If the results hold up to further scrutiny, they could improve the prospects for finding at least simple forms of extraterrestrial life on other planets or moons, including Saturn's moon Titan, astrobiologists say.

Astrobiologists have been using life on Earth as a basis for hunting for potential habitats beyond the third rock from the sun. But most of the attention has focused on what researchers offhandedly refer to as "life as we know it." Until now, biological canon has held that life on Earth is mainly built around a mix of six chemical elements: hydrogen, oxygen, carbon, sulfur, nitrogen, and phosphorus.

But a small number of scientists have been pushing the idea of "life as we don't know it," says Dirk Schulze-Makuch, an astrobiologist at Washington State University in Pullman, Wash., who counts himself as one of this small band.

"There could be different building blocks used, different types of elements, or different types of energy sources," he says.

And now, along comes a terrestrial form of life that can replace phosphorus with arsenic and thrive.

Revising the 'recipe' for life

Other bacteria in effect "breathe" arsenic or use it as a food source, converting it into something less harmful. But the newly discovered bacteria incorporate it into the very fabric of their most basic biological structures.

"It's an exciting result that basically made my day," says Dr. Schulze-Makuch of the discovery, made by a team led by US Geological Survey biochemist Felisa Wolfe-Simon.

It's as though "the recipes to make the fundamental molecules of life are open for negotiation," adds James Elser, a biologist at Arizona State University who was not part of the group making the discovery.

Dr. Wolfe-Simon says the hunt for organisms that might be based on different groups of chemical elements began when she noticed that some of the elements organisms use in very small amounts – such as iron, zinc, and molybdenum – had ready substitutes. These substitutes are similar enough to the elements they would replace that many organisms can use them as stand-ins if the originals are unavailable.

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