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Why Those Cool Arsenic Bacteria Are Not A New Form Of Life
Dec. 3 2010 - 11:09 am | 4,289 views | 1 recommendation | 2 comments
By MATTHEW HERPER
We're still a long way from Mos Eisley Image by popculturegeek.com via Flickr
The world is atwitter about the discovery of a strain of bacteria called GFAJ-1 that can build its DNA and proteins with poisonous arsenic instead of phosphorus. This is a stunning discovery, a triumph for Felisa Wolfe-Simon, the astrobiologist who led the work, and a big step forward for scientists who are trying to imagine what life is like on other worlds. But I think that a lot of the discussions that call this a completely new form of life are getting completely ahead of themselves.
Astrobiologists like the idea that life can be built with a completely different set of chemical building blocks because it means that life could then exist in all sorts of places that Earth-based living things would find intolerable. This is Arthur C. Clarke territory. He populated his book 201o "“ the sequel to the more famous 2001 "“ with all sorts of life forms that lived on Jupiter and its moons, some with alternate chemistry. And it would be undeniably cool if the building blocks of living things could differ.
The arsenic-eating bacterium, written up in the current issue of Science, provides a muted proof of concept for this idea. It's not so much a new form of life as evidence that you can teach the old form of life new tricks.
Wolfe-Simon and her colleagues found the critter in a lake in eastern California with high arsenic concentrations. They guessed that arsenic might be able to replace phosphorus in the microbe's body chemistry, and tried to grow it either in a solution with lots of phosphorus, or one with lots of arsenic.
Both approaches worked, and the bacteria grown in arsenic have high levels of arsenic in their DNA and also in their proteins and other structures. Moreover, they don't have phosphorus, considered a fundamental DNA building block. This is the first example of a life form that can live with a different set of basic chemicals.
But what's clear from Wolfe-Simon's publication in Science, but not from a lot of the press coverage, is that these bacteria didn't really like growing in arsenic. They grew 50% bigger because they suddenly developed big empty chambers in their cells, and the researches said they also became more fragile. It's possible that life first evolved with an arsenic-laced DNA molecule, and these bacteria are essentially switching back, but it seems far more likely that the GFAJ-1 are proof of life's amazing ability to adapt to even the most difficult conditions.
Gerald Joyce, of the Scripps Research Institute in La Jolla, puts this really well in the New York Times, telling science reporter Dennis Overbye that these critters are stuck on the same tree of life as dinosaurs, plants, and yeast. "œIt's a really nice story about [the] adaptability of our life form," Joyce told Overbye. "œIt gives food for thought about what might be possible in another world."
The big question is how life gets going in the first place. We don't really have answers here. Some scientists have speculated that life on Earth started in an "œRNA world" in which the chemical our cells now use only as a messenger served the roles of both genetic material (like DNA) and structure (now served by proteins.) Synthetic biologists have created alternative DNA- and RNA-like molecules. Could life have really started in some completely different soup of chemicals with different building blocks? It's hard to know without understanding how things got started here.
Answers are only going to come from further explorations for a "œshadow biosphere" by scientists like Wolfe-Simon and by the continuing efforts to engineer existing living things and to understand how they work. The field of custom-engineering microbes has become one of the hottest areas of alternative energy, with investments by tiny startups like Amyris and LS9 and giants such as Exxon and BP. This field, though not those companies, could be a source of more information. A synthetic organism that works by different chemicals entirely might actually be just as important as the new arsenic-eating GFAJ-1 bacterium.
Why Those Cool Arsenic Bacteria Are Not A New Form Of Life
Dec. 3 2010 - 11:09 am | 4,289 views | 1 recommendation | 2 comments
By MATTHEW HERPER
We're still a long way from Mos Eisley Image by popculturegeek.com via Flickr
The world is atwitter about the discovery of a strain of bacteria called GFAJ-1 that can build its DNA and proteins with poisonous arsenic instead of phosphorus. This is a stunning discovery, a triumph for Felisa Wolfe-Simon, the astrobiologist who led the work, and a big step forward for scientists who are trying to imagine what life is like on other worlds. But I think that a lot of the discussions that call this a completely new form of life are getting completely ahead of themselves.
Astrobiologists like the idea that life can be built with a completely different set of chemical building blocks because it means that life could then exist in all sorts of places that Earth-based living things would find intolerable. This is Arthur C. Clarke territory. He populated his book 201o "“ the sequel to the more famous 2001 "“ with all sorts of life forms that lived on Jupiter and its moons, some with alternate chemistry. And it would be undeniably cool if the building blocks of living things could differ.
The arsenic-eating bacterium, written up in the current issue of Science, provides a muted proof of concept for this idea. It's not so much a new form of life as evidence that you can teach the old form of life new tricks.
Wolfe-Simon and her colleagues found the critter in a lake in eastern California with high arsenic concentrations. They guessed that arsenic might be able to replace phosphorus in the microbe's body chemistry, and tried to grow it either in a solution with lots of phosphorus, or one with lots of arsenic.
Both approaches worked, and the bacteria grown in arsenic have high levels of arsenic in their DNA and also in their proteins and other structures. Moreover, they don't have phosphorus, considered a fundamental DNA building block. This is the first example of a life form that can live with a different set of basic chemicals.
But what's clear from Wolfe-Simon's publication in Science, but not from a lot of the press coverage, is that these bacteria didn't really like growing in arsenic. They grew 50% bigger because they suddenly developed big empty chambers in their cells, and the researches said they also became more fragile. It's possible that life first evolved with an arsenic-laced DNA molecule, and these bacteria are essentially switching back, but it seems far more likely that the GFAJ-1 are proof of life's amazing ability to adapt to even the most difficult conditions.
Gerald Joyce, of the Scripps Research Institute in La Jolla, puts this really well in the New York Times, telling science reporter Dennis Overbye that these critters are stuck on the same tree of life as dinosaurs, plants, and yeast. "œIt's a really nice story about [the] adaptability of our life form," Joyce told Overbye. "œIt gives food for thought about what might be possible in another world."
The big question is how life gets going in the first place. We don't really have answers here. Some scientists have speculated that life on Earth started in an "œRNA world" in which the chemical our cells now use only as a messenger served the roles of both genetic material (like DNA) and structure (now served by proteins.) Synthetic biologists have created alternative DNA- and RNA-like molecules. Could life have really started in some completely different soup of chemicals with different building blocks? It's hard to know without understanding how things got started here.
Answers are only going to come from further explorations for a "œshadow biosphere" by scientists like Wolfe-Simon and by the continuing efforts to engineer existing living things and to understand how they work. The field of custom-engineering microbes has become one of the hottest areas of alternative energy, with investments by tiny startups like Amyris and LS9 and giants such as Exxon and BP. This field, though not those companies, could be a source of more information. A synthetic organism that works by different chemicals entirely might actually be just as important as the new arsenic-eating GFAJ-1 bacterium.
