New microbe defies “law” of life

California's Mono Lake

There was big news from NASA today.

A team of scientists from NASA’s Astrobiology Institute and the U.S. Geological Survey in Menlo Park, Calif., announced it has found a microbe that exists in a way that was never thought possible.

Felisa Wolfe-Simon

The group, led by Felisa Wolfe-Simon, has found a bacterium that “eats” and uses toxic arsenic,  substituting the arsenic for phosphorus in its essential functions, including building new cells.

In all lifeforms that scientists have studied so far, the “backbone” of DNA is made of sugar and phosphorus in the form of phosphate. In this microbe, arsenic bonds with the sugar to make a new type of DNA.

This is a really big deal. As most science students know, there are six elements that are thought of as the “building blocks” of life – carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. (Sometimes they are written like this: CHONPS.) When scientists consider whether other environments may be hospitable to life – like another planet, for example – one of the things they consider is the availability of CHONPS.

This new microbe was found in mud from the bottom of California’s Mono Lake. Mono Lake is located in the eastern part of the Sierras. The lake is volcanic in origin, and now a closed basin, meaning no rivers or streams feed it fresh water, and none carry water away from the lake. (Once upon a time, the lake had feeder streams, but they were diverted by the Los Angeles Department of Water and Power and the lake was left to dry up and die.) As a result, all of the minerals and substances naturally found in a lake are very concentrated there. Mono Lake is almost three times as salty as the ocean. It is highly alkaline and rich in carbonates, phosphorus, arsenic and sulfur. It is filled with shrimp, flies and algae that can survive the lake’s strange chemistry.

So what makes NASA so interested in stuff on the bottom of a lake? Well, think about it this way: When astrobiologists look for life on other planets, they usually look for planets with environments like Earth, that include CHONPS. Now they can now vastly expand their searches to include other places and planets.

“We’ve cracked open the door to what’s possible for life elsewhere in the universe,” said Wolfe-Simon. “What else might we find?”

Resources:

Here is a bigger story about the microbe’s discovery in the New York Times.

Here is a great website for learning more about Mono Lake, including its geological and human-influenced histories.

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