Debate over Arsenic Bacteria: A Skeptic’s Viewpoint
December 9, 2010 Leave a comment
Probably all of you have received the news of newly discovered so called ‘Arsenic Bacterium’ that replaced phosphorus with highly toxic Arsenic. 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.
[Image Details: This scanning electron micrograph shows a strain of the arsenic-eating bacterium called GFAJ-1. Credit: Science/AAAS.]
This finding of an alternative biochemistry makeup will alter biology textbooks and expand the scope of the search for life beyond Earth. Carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur are the six basic building blocks of all known forms of life on Earth. Phosphorus is part of the chemical backbone of DNA and RNA, the structures that carry genetic instructions for life, and is considered an essential element for all living cells. Phosphorus is a central component of the energy-carrying molecule in all cells (adenosine triphosphate) and also the phospholipids that form all cell membranes. Arsenic, whichis chemically similar to phosphorus, is poisonous for most life on Earth. Arsenic disrupts metabolic pathways because chemically it behaves similarly to phosphate.
The newly discovered microbe, strain GFAJ-1, is a member of a common group of bacteria, the Gammaproteobacteria. In the laboratory, the researchers successfully grew microbes from the lake on a diet that was very lean on phosphorus, but included generous helpings of arsenic. When researchers removed the phosphorus and replaced it with arsenic the microbes continued to grow. Subsequent analyses indicated that the arsenic was being used to produce the building blocks of new GFAJ-1 cells. The key issue the researchers investigated was when the microbe was grown on arsenic did the arsenic actually became incorporated into the organisms’ vital biochemical machinery, such as DNA, proteins and the cell membranes. A variety of sophisticated laboratory techniques was used to determine where the arsenic was incorporated.
This was big news, since scientists had regarded phosphorus as one of six key ingredients — along with carbon, hydrogen, nitrogen, oxygen and sulfur — that all life on Earth needs to survive. But over the weekend, some outside scientists began to question the team’s findings. Some aren’t convinced that GFAJ-1 actually takes arsenic up into its DNA, saying that the researchers may have just detected arsenic stuck to the outside of the microbe’s DNA. Other researchers contend that the growth medium contained enough phosphorus — as a contaminant — for GFAJ-1 to scratch out a living without having to swap it out for arsenic. Microbes are known to subsist on minuscule amounts of phosphorus elsewhere, such as the Sargasso Sea, critics said. And other scientists pointed out that arsenate compounds are extremely unstable in water, breaking down in minutes without some kind of compensatory stabilizing mechanism, such as special molecules to keep the compound intact. Wolfe-Simon and her teamdunked GFAJ-1 in water during the analysis process, yet the microbe’s DNA didn’t get sliced into many tiny pieces — it remained in large chunks.
This further hints that the microbe’s DNA contained the”normal” phosphate rather than arsenate, some said. I don’t know how skeptical they are. Why to flourish your mind just into possibility? Critics need to repeat the experiment themselves and challenge the findings reported in journal. It is how really science works rather making vague arguments and airing absurd speculations even after declaring the specifications. Some also argued that it is however, not so possible as it would be disintegrated immediately in presence of water.
“I think we had enough to get the point out,” Oremland said.”Certainly the [paper’s] reviewers liked it, and now the community is going to judge.”
He also said the small amount of phosphorus present in the growth medium as a contaminant wasn’t as big a dealas the paper’s critics have alleged.
“There’s a smidgen of phosphorus in the medium,” he said. “We didn’t do anything fancy to get rid of it. But it’s not enough to sustain growth. That’s very clear.”
“They may prove us wrong, or they may reproduce the results and find new stuff,” he said. “It’s the way the process works.”
I’m agree with Oremland’s view. Skeptics need to repeat experiment and should repeat their findings rather airing dubious speculations. If they can prove their results wrong, it would be welcomed.
[Credit: Nasa and LiveScience]