Poisoned life?

Remember the murder mystery "Arsenic and old lace" , where a couple of old ladies did away with guests using arsenic poisoning?  Researchers in California have found a life form that uses arsenic in place of phosphorus.  Big deal one might say.  But this is really interesting as phosphorus is one of the six elements that all living things that we know of use to build their basic molecules.

This discovery dates back to August 2008^[1] when Scientific American reported the use of arsenic in the photosynthetic processes of bacteria in Lake Mono in California.  This lake is rich in arsenic and the bacteria are one of the few organisms that can thrive there.  The bacteria use the energy of the sun to strip two electrons from the arsenic atoms instead of using water.  The electrons are passed along the electron transport chain driving the chemiosmosis process of pumping hydrogen ions across the mesosome membrane.  As the hydrogen ions accumulate, there is a concentration gradient and the hydrogen ions flow back and the process ATP is made from ADP and inorganic phosphorus.

A more recent report today in Scientific American^[2]  talks about how the bacteria replace the phosphorus with arsenic in the most important molecules of living things;  DNA, RNA, ATP and possibly phospholipids in membranes.  Arsenic is a respiratory poison in that it competitively inhibits the oxidative phosphorylation process of ATP production in the mitochondria.

These stories are relevant to IB Biology through the structure of DNA, ATP use and production, food chains of organisms that feed on these bacteria and of course the natural selection for such life forms.