Arsenic-loving Bacteria

NASA-funded astrobiology research has changed the fundamental knowledge about what comprises all known life on Earth.

Researchers conducting tests in the harsh environment of Mono Lake in California have discovered the first known microorganism on Earth able to thrive and reproduce using the toxic chemical arsenic. The microorganism substitutes arsenic for phosphorus in its cell components.

"The definition of life has just expanded," said Ed Weiler, NASA's associate administrator for the Science Mission Directorate at the agency's Headquarters in Washington. "As we pursue our efforts to seek signs of life in the solar system, we have to think more broadly, more diversely and consider life as we do not know it." ¹

The discovery of an organism that thrives on otherwise poisonous arsenic broadens our thinking about the possibility of life on other planets, and begs a rewrite of biology textbooks by changing our understanding of how life is formed from its most basic elemental building blocks. ²

In a bombshell that upends long-held assumptions about the basic building blocks of life, scientists have discovered a whole new type of creature: a microbe that lives on arsenic. It is unlike every other lifeform on the planet - from the simplest plant to the most complex mammal. ³

The discovery of such odd life in our own backyard is a big boost for those searching the skies for extraterrestrials.

Such research findings prove that "shadow" creatures live in extreme environments previously thought uninhabitable. So here are the provocative questions posed by this finding: Are there other microbes than can do this? And could such creatures evolve into intelligent life, elsewhere? ⁴

This finding is important because it adds an extra criterion for the search of life on other planets. Historically, astronauts on space missions looked for evidence of life on other planets by seeing if their samples had the basic chemical elements of life.  Arsenic was not one of those elements until this recent discovery.  This means that there may have been samples they found that actually had signs of sustaining life. ⁵

So, theoretically speaking, life could exist on Venus which is extremely hot and acidic, or, it can exist on Mars where it’s extremely cold and gaseous. ⁶

A cryptic announcement from NASA in November said that the agency had important astrobiology news, leading many to speculate that it was set to unveil extraterrestrial life. Instead, during a media conference on 2 December, researchers announced the discovery of ordinary earthly bacteria from Mono Lake in California that seemed to do something extraordinary — use arsenic as a building block for DNA and proteins, in place of the phosphorus relied on by other organisms. But as soon as the unprecedented finding was made public, it drew sharp criticism from the scientific community. Biochemists took to the blogosphere, attacking the methodology and assumptions of the original research and provoking a flurry of articles in the media. Further work will be needed to settle whether the bacteria actually do use arsenic in their biochemistry as opposed to just cleverly thwarting its toxic effects. ⁷

In December, the bullets were flying furiously over a report about a microbe converted into an arsenic-loving, alien-like species proving that life on other worlds can be very different from Earth’s.

Oh wait. That was the hype. NASA’s clever PR machine leaked just enough information about the announcement for this new study to compete for media attention with celebrity divorces and athlete arrests. … it turned out to be a simple case of an earthly species learning to substitute arsenic for phosphorus in its diet, as Rachel Ehrenberg describes in this issue (Page 5). ⁸

NASA's Astrobiology Program in Washington contributed funding for the research through its Exobiology and Evolutionary Biology program and the NASA Astrobiology Institute. NASA's Astrobiology Program supports research into the origin, evolution, distribution, and future of life on Earth. ⁹

Among the goals of these programs is determining the evolution of genes, metabolic pathways, and microbial species on Earth in order to understand the potential for life on other worlds. Wolfe-Simon’s discovery represents the first time in the history of biology that an organism has been found to use a different element to build one of its most basic structures. ¹⁰