The recent announcement by NASA scientists and their collaborators that the GFAJ-1 strain of the Halomonadaceae bacteria provides hints into the potential biology of alien life-forms and the response of the media and scientific community to this claim have revealed several disturbing trends. These include the desperation of a government-funded science agency to generate publicity at a time when its financial support is in jeopardy; the inadequacy of the experiments by these researchers to support their conclusions; the relatively poor peer-review by one of the most prestigious of scientific journals; and the extra-hype added by the mass media. One rather positive aspect of this affair is the rapid response of the scientific community to question and challenge the most poorly supported and far reaching claims. It is likely that they will be disregarded much faster than the previous announcement by NASA of petrified Martian life in an Antarctic meteorite.
A few of my colleagues as well as numerous bloggers have noted that the NASA publicity machine has been coincidently cranked up at a time when the next US budget, including the funding for NASA, is under question. The discovery of the model organism described in the Wolfe-Simon et al. paper in Science is actually not new. Since the mid-nineties, the ongoing study of various strains of Halomonadaceae bacteria and their respiration of arsenic at Mono Lake, the Aberjona Watershed and elsewhere has been reported by Dr. Ronald Oremland (the senior author of the Wolfe-Simon et al. paper) and independently by others.
The central claim of the new Wolfe-Simon et al. study is that arsenic can substitute for phosphorus to sustain the growth of the GFAJ-1 bacterial strain, and some evidence is offered that the arsenic is incorporated into macromolecules such as nucleic acids and proteins. The GFAJ-1 cells were cultivated in the near absence of phosphorus in the growth media in the presence of arsenic. However, the media used in the study apparently had about 3 M phosphorus, and one wonders whether phosphorus may have also been introduced with the culture plates that may have been pre-washed with phosphate-containing detergents. In any event, the cultured GFAJ-1 cells were still observed to contain phosphorus at about 1% of the levels seen in cells grown in the presence of high phosphorus. Even under these conditions, bathing in medium containing arsenic, these cells still featured 100-times more phosphorus than arsenic. Moreover, the levels of arsenic incorporated into the phosphorus-depleted bacteria was not that much different from phosphorus-supplemented GFAJ-1 cells grown without arsenic. Ideally, a synchrotron X-ray analysis of arsenic in biomolecules should have been undertaken for both the phosphorus-fed and starved populations of the bacteria rather than just the phosphorus-depleted cells as was performed in the study.
Despite the speculations offered in the Wolfe-Simon et al. paper, no conclusive evidence was provided that any arsenic actually replaced phosphorus in the DNA backbone of the GFAJ-1 cells. To incorporate arsenic into nucleotides and proteins, the arsenic would have to be presented with the arsenic-containing equivalent of adenosine tri-phosphate (ATP), i.e. adenosine tri-arsenate (ATAs). No evidence was obtained for the presence of ATAs in the GFAJ-1 bacteria. In fact, I have been unable to find any reports of ATAs in any life-form from PubMed or Google searches.
While arsenic and phosphorus are highly related in the periodic table of elements, the arsenic atom is slightly more than double the molecular mass of phosphorus. As atoms get larger, the electronic structure of the atom, particularly those parts that participate in chemical bonds, become increasingly diffuse. Consequently, arsenate esters are very unstable and hydrolyze markedly faster than phosphate esters. This instability of arsenate ester linkages really restricts their utility in the synthesis of macromolecules like DNA. Furthermore, the instability of arsenylation of proteins, would preclude
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The recent announcement by NASA scientists and their collaborators that the GFAJ-1 strain of the Halomonadaceae bacteria provides hints into the potential biology of alien life-forms and the response of the media and scientific community to this claim have revealed several disturbing trends. These include the desperation of a government-funded science agency to generate publicity at a time when its financial support is in jeopardy; the inadequacy of the experiments by these researchers to support their conclusions; the relatively poor peer-review by one of the most prestigious of scientific journals; and the extra-hype added by the mass media. One rather positive aspect of this affair is the rapid response of the scientific community to question and challenge the most poorly supported and far reaching claims. It is likely that they will be disregarded much faster than the previous announcement by NASA of petrified Martian life in an Antarctic meteorite. A few of my colleagues as well as numerous bloggers have noted that the NASA publicity machine has been coincidently cranked up at a time when the next US budget, including the funding for NASA, is under question. The discovery of the model organism described in the Wolfe-Simon et al. paper in Science is actually not new. Since the mid-nineties, the ongoing study of various strains of Halomonadaceae bacteria and their respiration of arsenic at Mono Lake, the Aberjona Watershed and elsewhere has been reported by Dr. Ronald Oremland (the senior author of the Wolfe-Simon et al. paper) and independently by others. The central claim of the new Wolfe-Simon et al. study is that arsenic can substitute for phosphorus to sustain the growth of the GFAJ-1 bacterial strain, and some evidence is offered that the arsenic is incorporated into macromolecules such as nucleic acids and proteins. The GFAJ-1 cells were cultivated in the near absence of phosphorus in the growth media in the presence of arsenic. However, the media used in the study apparently had about 3 M phosphorus, and one wonders whether phosphorus may have also been introduced with the culture plates that may have been pre-washed with phosphate-containing detergents. In any event, the cultured GFAJ-1 cells were still observed to contain phosphorus at about 1% of the levels seen in cells grown in the presence of high phosphorus. Even under these conditions, bathing in medium containing arsenic, these cells still featured 100-times more phosphorus than arsenic. Moreover, the levels of arsenic incorporated into the phosphorus-depleted bacteria was not that much different from phosphorus-supplemented GFAJ-1 cells grown without arsenic. Ideally, a synchrotron X-ray analysis of arsenic in biomolecules should have been undertaken for both the phosphorus-fed and starved populations of the bacteria rather than just the phosphorus-depleted cells as was performed in the study. Despite the speculations offered in the Wolfe-Simon et al. paper, no conclusive evidence was provided that any arsenic actually replaced phosphorus in the DNA backbone of the GFAJ-1 cells. To incorporate arsenic into nucleotides and proteins, the arsenic would have to be presented with the arsenic-containing equivalent of adenosine tri-phosphate (ATP), i.e. adenosine tri-arsenate (ATAs). No evidence was obtained for the presence of ATAs in the GFAJ-1 bacteria. In fact, I have been unable to find any reports of ATAs in any life-form from PubMed or Google searches. While arsenic and phosphorus are highly related in the periodic table of elements, the arsenic atom is slightly more than double the molecular mass of phosphorus. As atoms get larger, the electronic structure of the atom, particularly those parts that participate in chemical bonds, become increasingly diffuse. Consequently, arsenate esters are very unstable and hydrolyze markedly faster than phosphate esters. This instability of arsenate ester linkages really restricts their utility in the synthesis of macromolecules like DNA. Furthermore, the instability of arsenylation of proteins, would preclude