Field of Science


NASA, You're Such a Tease.

When NASA announced that they were going to hold a press conference about "an astrobiology finding that will impact the search for extraterrestrial life," I was pretty excited--especially when I read that the details had been embargoed (that is, people at the journal publishing the paper weren't allowed to talk about it ahead of time). To make sure we got the hint, NASA reminded readers that "Astrobiology is the study of the origin, evolution, distribution and future of life in the universe."

What would the discovery be? The odds that SETI had finally received their alien phone call seemed slim. But maybe researchers had spotted solid evidence of alien bacteria on Saturn's moon Titan, or some other rock in the solar system. After all, there have been some tantalizing hints in that direction recently.

The press conference was schedule for 2:00 ET yesterday, but a few hours earlier, the story leaked all over the internet. According to Gizmodo (whose story has since been updated), astrobiologist Felisa Wolfe-Simon had discovered an exciting new bacteria species in a weird California lake. These bacteria, the story said, were not made of the same buildings blocks as the rest of Earth's life. While all other known life is made of six primary ingredients (carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur), these bacteria used arsenic instead of phosphorus.

Phosphorus is part of the backbone of DNA. The discovery of a life form that built its DNA out of different molecules would indeed be huge. Was it evidence that life had arisen on Earth not once, but twice? Or, since NASA was promoting this as an astrobiology story, did they believe that the bacteria had traveled to Earth from a meteorite--evidence for alien life?

When NASA released its own story a few hours later, the message was slightly different.

What Wolfe-Simon found was a bacterial strain called GFAJ-1, a member of a common bacterial family. Since the bacteria live in a lake that contains a lot of arsenic, and arsenic atoms are very similar to phosphorus (this is why arsenic is usually poisonous--it gets into the bodily pathways where phosphorus is supposed to be), she wondered whether these bacteria would be able to safely use arsenic as a substitute for phosphorus.

She cultured the bacteria (grew them in a lab) using sediment from their home lake and increasingly strong concentrations of arsenic. Over many generations of bacteria, she gradually replaced all the phosphorus in their food with arsenic. And they lived! She found evidence that the bacteria had successfully incorporated arsenic into their proteins, and even into the backbone of their DNA.

No one has ever shown before that a life form can swap out one of its vital building blocks (though arsenic-eating bacteria aren't new). But is this the earth-shaking discovery the headlines are claiming?

Wolfe-Simon did not show, and doesn't claim to have shown, that any bacteria function this way naturally. She did not demonstrate that bacteria in the lake actually substitute arsenic for phosphorus. To get her own plates of bacteria to work this way, she gradually weaned them off phosphorus and added arsenic. As writer Ed Yong points out, she may have artificially selected for arsenic-eating bacteria--that is, forced their rapid evolution by killing off the non-arsenic-eaters in each generation. And since the arsenic-users grew in exponentially lower amounts than the phosphorus-users, it seems impossible that any of them could exist in nature. They'd immediately be outcompeted by their phosphorus-using neighbors.

The link to alien life is tenuous, at best. "If something here on Earth can do something so unexpected, what else can life do that we haven't seen yet?" Wolfe-Simon says.

It's an interesting finding, but it's not about extraterrestrial life; it's about a quirky kind of bacteria created in a lab. It's too bad that NASA allowed the hype to drown out the reality.

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