News Update: New Research Says 2010 NASA Finding of Arsenic-Based DNA Inconclusive



An arsenic-eating bacterium offering hope for life living on alien worlds was announced by NASA scientists in January of 2010. As reported then in the journal Science, a team led by Felisa Wolfe-Simon of the NASA Astrobiology Institute in Menlo Park, Calif., who has been conducting research at Mono Lake California for years and led the experiment, had discovered an "alien life-form" on Earth: bacteria that replaced a key building block in DNA –phosphorus–with arsenic.

"Biological dependence on the six major nutrient elements carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus is complemented by a selected array of other elements, usually metal(loid)s present in trace quantities that serve critical cellular functions, such as enzyme co-factors. There are many cases of these trace elements substituting for one another," reported the NASA study. "However, there are no prior reports of substitutions for any of the six major elements essential for life. Here we present evidence that arsenic can substitute for phosphorus in the biomolecules of a naturally-occurring bacterium."

The scientists said that they had trained a bacterium taken from the bottom of Mono Lake in California to eat and grow on a diet of arsenic, in place of phosphorus — one of six elements considered essential for life — opening up the possibility that organisms could exist elsewhere in the universe (or even here on Earth) using unknown alien biochemical powers.

Phosphorus is one of six chemical elements that have long been thought to be essential for all life on Earth until now. The others are carbon, oxygen, nitrogen, hydrogen and sulfur. Phosphorus chains are the backbone building block of DNA and its chemical bonds, particularly in a molecule known as adenosine triphosphate, the principal means by which biological creatures store energy.

While nature has been able to engineer substitutes for some of the other elements that exist in trace amounts for specialized purposes — like iron to carry oxygen — until now the NASA Mono Lake cliams, there has been no substitute for the basic six elements. * NASA scientists said the results, if confirmed, would dramatically extend our understanding of what life could be and where it could be.

Felisa Wolfe-Simon told the New York Times, “This is a microbe that has solved the problem of how to live in a different way.” This story is not about Mono Lake or arsenic, she added, but about “cracking open the door and finding that what we think are fixed constants of life are not.” * Arsenic sits right beneath phosphorus in the periodic table of the elements and shares many of its chemical properties -a chemical closeness is what makes it toxic, Dr. Wolfe-Simon said, "allowing it to slip easily into a cell’s machinery where it then gums things up, like bad oil in a car engine."

In an earlier paper in The International Journal of Astrobiology, Felisa Wolfe-Simon and Ariel Anbar and Paul Davies, both of Arizona State University, predicted the existence of arsenic-loving life forms.

According to the article in Science, a bacterium known as strain GFAJ-1 of the Halomonadaceae family of Gammaproteobacteria, proved to grow the best of the microbes from the lake, although not without changes from their normal development. The cells grown in the arsenic came out about 60 percent larger than cells grown with phosphorus along with large, empty internal spaces.

By labeling the arsenic with radioactivity, the NASA Astrobiology researchers concluded that arsenic atoms had taken up position in the microbe’s DNA as well as in other molecules within it. It was inconclusive, however, that there was arsenic in the backbone of working DNA.

The new studies, also published in Science, found that the bacterium did in fact grow in the conditions described in the 2010 study, but when the amount of phosphorous was reduced even further than in Wolfe-Simon's experiments, GFAJ-1 grow came to a halt. University of British Columbia iologist Rosemary Redfield writes in the new study, no signs of arsenic could be found in GFAJ-1's DNA.

The new studies concluded that the arsenic-loving extremeophile does need phosphorous to grow, but shockingly tiny amounts of it.

Wolfe-Simon, now with the Lawrence Berkeley National Laboratory, stands by her findings according to National Geographic. The new paper, she said, shows only that the arsenic doesn't show up in the DNA, not that the organism never uses it.

The Daily Galaxy via The New York Times, National Geographic and Science 


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