Answer Happy

Two days after the paper was released on the Science website, Rosie Redfield, a microbiologist at the University of British Columbia, posted her critique of the paper on her blog (Redfield, 2010). Her tweet announcing this new post did not mince words: Follow Rosie Redfield Rosedeld I've posted a full analysis of NASA's arsenic bacteria paper at http://rrresearch.blogspot.com. Bottom line: it's shamefully bad science. Reply Faw 20 ETT VOTED 9:07FM-410 Here are some of the highlights of Rosie's critique of the paper's methodologies and conclusions: A. Felisa's team claims that the cells grown in a medium with no added phosphate or arsenate failed to grow. A closer inspection of the data shows this to be inaccurate; the cells did grow, albeit more slowly. Also, Rosie calculated that the trace amount of phosphorus contaminating the medium ingredients was sufficient to sustain growth of the bacteria in the "no phosphate condition. B. A bacterial genome composed of 2 x 10^6 base pairs (a midrange genome size for bacteria) contains 4 x 10^6 phosphorus atoms. Using "back of the envelope calculations," the data available in Table 2, and the known ratio of phosphorus and carbon in a DNA molecule, Rosie calculates that the genome of a GFAJ-1 bacterium grown in the presence of arsenate contains 400 atoms of arsenic while bacteria grown in the presence of phosphate have 200 atoms of arsenic in their genome. C. Using agarose pieces to calculate the arsenic-to-carbon ratio is a mistake, because agarose (a carbohydrate) contains many atoms of carbon, and therefore the arsenic-to-carbon ratio will depend on factors such as the size of the agarose chunk used in the experiment. D. Rosie brings up the chemical instability of arsenate compared to phosphate. The bonds between the phosphorus atoms and the oxygen atoms in phosphate are very stable and break down in timescales measured in thousands of years (300,000 years is the half-life of that bond). Meanwhile, arsenate is known to be much less stable and to break down in less than a second (0.06 seconds is the half-life) (Fekry et al., 2011). Rosie presented a few other criticisms, but these should suffice for the purpose of this discussion. QUESTION - Concerning point C, propose a proper control for this experiment. Explain the reason?