In response to Malcolm McCallum's post on the NASA-funded study on bacteria that live off arsenic in place of phosphorus, I agree that the media has greatly hyped up its conclusions. Furthermore, I want to bring attention to the strong criticisms of the study among many microbiologists, one scientist from the University of Colorado going as far as to say that the paper should never have been published (see http://www.slate.com/id/2276919/pagenum/all/).
Among several issues identified with the study, a couple notable ones are: 1. When the authors stopped feeding phosphorus to the bacteria and replaced it with arsenic, the bacteria kept growing, implying that the bacteria were living off the arsenic. However, they were also feeding the bacteria a salt that had been contaminated with phosphorus. Granted, it was a very tiny amount of phosphorus, but many other bacteria species have been known to live off so little phosphorus, so this bacterium could have been eking out a living from the contaminated salts. 2. The study gives evidence for the bacteria incorporating arsenic compounds in their DNA. Arsenic compounds break down in water, so if there was arsenic in the DNA, when submerged in water the DNA should have broken into many small fragments. Instead of this, however, the DNA remained in a small number of large chucks, suggesting that the DNA was composed of more stable phosphorus compounds. Rosie Redfield, a microbiologist at the University of British Columbia, posted a much more extensive and detailed review of the arguments against the study's findings at: http://rrresearch.blogspot.com/2010/12/arsenic-associated-bacteria-nasas.html Regards, Briana Abrahms
