Remember arsenic life? In 2010 NASA researchers thought they'd found evidence that certain bacteria could use arsenic in their DNA where all other forms of life on Earth use phosphate. Then it turned out their research was really flawed. Then it turned out they were wrong. In general, there was a to-do.
Fast forward to this month, when scientists from the Weizmann Institute of Science in Rehovot, Israel published a study in which they were trying to figure out how bacteria can tell the difference between phosphate and arsenate and "know" to prefer the phosphate. They used phosphate-collecting proteins from four different species of bacteria in their research, including the one that had been at the center of the arsenic life controversy. And along the way, they discovered a fun twist to that story.
This new study suggests that "arsenic life" bacteria is, indeed, able to survive in arsenate-heavy solutions where other bacteria fail. But, the Weizmann researchers say their data shows that success isn't due to a preference for arsenic, or even an ability to use it. Instead, "arsenic life" is probably just much, much, much, much better at collecting and using every tiny trace of phosphate it can get its metaphorical paws on.
The researchers looked at five types of phosphate-binding protein — which bind phosphate in a molecular pathway that brings it into the cells — from four species of bacteria. Two of the bacterial species were sensitive to arsenate and two were resistant to it. To test how effective these proteins were at discriminating between phosphate and arsenate, the researchers put them in solution with a set amount of phosphate and different concentrations of arsenate for 24 hours, and then checked which of the molecules the proteins would bind to.
Their threshold for when ‘discrimination’ broke down was when 50% of the proteins ended up bound to arsenate — indicating that the ability to discriminate had been overwhelmed. Even in solutions containing 500-fold more arsenate than phosphate, all five proteins were still able to preferentially bind phosphate. And one protein, from the Mono Lake bacterium, could do so at arsenate excesses of up to 4,500-fold over phosphate.
... The latest paper shows that the “arsenic monster” GFAJ-1 goes to a huge amount of effort, “even more than other life”, to avoid arsenate, says Wolfgang Nitschke from the Mediterranean Institute of Microbiology in Marseilles, France, who co-authored a commentary questioning the conclusion that GFAJ-1 could replace phosphate with arsenate.
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