Do aliens eat arsenic for breakfast?

Artist's impression of an exoplanet

The discovery of weird, arsenic-eating life on Earth raises questions about what varieties of life might exist elsewhere in the cosmos. Artist's impression, courtesy G. Bacon / STScI / AVL.

  • Micro-organism found to live on deadly arsenic
  • Raises the stakes on what potential alien life could be like
  • Scientists think there could be more “weird” life here on Earth

CAN YOU IMAGINE eating toxic waste for breakfast? Researchers have discovered a bacterium that can live and grow entirely off arsenic, reports a new study.

The findings point for the first time to a micro-organism that is able to use a toxic chemical (rather than the usual phosphate) to sustain growth and life.

Arsenic is normally highly toxic to living organisms because it disrupts metabolic pathways, but chemically it behaves in a similar way to phosphate.

Scientists have previously found organisms that can chemically alter arsenic; and these organisms have been implicated in ground water poisoning events in Bangladesh and other places in Asia when people have shifted to using borehole or well water to avoid cholera.

Felisa Wolfe-Simon and Ronald Oremland

Felisa Wolfe-Simon, right, a NASA astrobiology research fellow, and Ronald Oremland, an expert in arsenic microbiology, examine sediment from Mono Lake. Photo by Henry Bortman.

Now, Felisa Wolfe-Simon, a NASA astrobiology research fellow in residence at the US Geological Survey, and colleagues have found a bacterium able to completely swap arsenic for phosphorus to the extent that it can even incorporate arsenic into its DNA.

“Life as we know it requires particular chemical elements and excludes others,” says Arizona State University (ASU) professor Ariel Anbar, a biogeochemist and astrobiologist who directs the astrobiology program at ASU.

“But are those the only options? How different could life be?” Anbar and Wolfe-Simon are among a group of researchers who are testing the limits of life’s chemical requirements.

The salt-loving bacteria, a member Halomonadaceae family of proteobacteria, came from the toxic and briny Mono Lake in California.

In the lab, the researchers grew the bacteria in Petri dishes in which phosphate salt was gradually replaced by arsenic, until the bacteria could grow without needing phosphate, an essential building block for various macromolecules present in all cells, including nucleic acids, lipids and proteins.

Using radio-tracers, the team closely followed the path of arsenic in the bacteria; from the chemical’s uptake to its incorporation into various cellular components.

Arsenic had completely replaced phosphate in the molecules of the bacteria, right down to its DNA.

Weird life could be all around us

Cosmologist and ASU professor Paul Davies has previously speculated that forms of life different from our own, dubbed “weird life,” might even exist side-by-side with known life on Earth, in a sort of “shadow biosphere.”

Halomonadaceae proteobacteria

Halomonadaceae proteobacteria have been found to eat deadly arsenic. Image courtesy of Science/AAAS.

The particular idea that arsenic, which lies directly below phosphorous on the periodic table, might substitute for phosphorus in life on Earth, was proposed by Wolfe-Simon and developed into a collaboration with Davies and Anbar.

Their hypothesis was published in January 2009, in a paper titled “Did nature also choose arsenic?” in the International Journal of Astrobiology.

Davies predicts that the new organism “is surely the tip of a big iceberg, and so has the potential to open up a whole new domain of microbiology.”

It is not only scientists, however, who will be interested in this discovery.

“Our findings are a reminder that life-as-we-know-it could be much more flexible than we generally assume or can imagine,” says Wolfe-Simon, noting that because microbes are major drivers of biogeochemical cycles and disease this study may open up a whole new chapter in biology textbooks.

“Yet, this story isn’t about arsenic or Mono Lake,” Wolfe-Simon says. “If something here on Earth can do something so unexpected, what else can life do that we haven’t seen yet? Now is the time to find out.”

Adapted from information issued by Arizona State University / Science / AAAS / Henry Bortman.

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