Arsenic Fueling Calif. Lake Bacteria

Aug. 14, 2008 -- A deadly toxin, arsenic is known for its ability to end life. But new organisms found floating in Mono Lake in California depend on the poison to survive, even using it along with sunlight to make food through photosynthesis.

Since the 1990s, scientists have discovered about 20 species of bizarre bacteria that "breathe" arsenic. They are typically found in environments where oxygen is scarce and have been forced to survive on whatever strange substance is easily available.

"Just like you and I inhale oxygen and breathe out carbon dioxide, these bugs breathe in Arsenic +3 and breathe out Arsenic +5," said Ronald Oremland of the United States Geological Survey in Menlo Park, Calif.

Arsenic +3 is the most poisonous form of the element, because it acts much like phosphorous. Most life on Earth needs phosphorous to build the molecule adenosine triphosphate (ATP), which supplies cells with energy. Arsenic can substitute for phosphorous and upset the ATP molecule, essentially starving cells to death.

In the arsenic-rich, oxygen-poor waters of Mono Lake, Oremland and a team of researchers found that bacteria turn the lethal toxin to their advantage through photosynthesis. With the help of sunlight, the microbes oxidize Arsenic +3 ions into Arsenic +5 ions, stripping away electrons in the process. The electrons are then used as the energetic push needed to build ATP.

The research will be published in the Aug. 15 issue of Science.