Arsenic or Phosphorus based DNA?

Just over a year ago, I wrote a blog "Arsenic based life forms?" a study was published suggesting that a bacterium could be using arsenic instead of phosphorus in building its DNA and other molecules.  This would be unique as arsenic is thought to be toxic to life forms.

Recently, another study has been put onto the Internet refuting the original claim.  This is how science works:

• Observations are made - life exists in waters with high levels of arsenic and other toxic elements.
• Hypotheses are created - If bacteria do not have phosphorus but are exposed to arsenic, will the arsenic be taken up and used?  Arsenic is in the same periodic table group as phosphorus so perhaps the similar chemical characteristics will work.
• Testing the hypothesis - controlled experiments are devised to test the ideas. Controls in the procedure ensure that the only change occurring would be due to the change of only one variable, in this case the amount of phosphorus available to the bacteria.
• Analysis of results - strict rules about how the data are treated so that little or no bias can enter into the analysis.  One way of doing this is with a double blind study which means that neither party analysing the data knows the exact content of the samples but return their reports to those who have marked the samples.
• Peer review and publishing - the traditional method involves having other scientists in the field review the work and critique the protocols and how the data were analysed. Scientific journals such as Nature, Science, The Lancet among others are recognised for their peer review process to publish scientific studies.

The recent study refuting the arsenic in DNA study was a Internet blog post from and not a peer reviewed journal article.  This is causing a stir in the scientific community about open source scientific research and writing as much as the reason for the study- whether DNA could contain arsenic or not.

This article could be read to generate discussions about the scientific process and ethical research in Biology as well as in TOK ( Natural Sciences as a Way of Knowing).

I will be following this story to see how things develop.