To test her hypothesis, Wolfe-Simon collected mud from Mono Lake, California, a desert body of water known for having high arsenic levels, and grew the microorganisms from it in increasing concentrations of arsenate. She didn't add any phosphate or other phosphorus-containing compounds to the growth medium, as is typically done to sustain microbes. Instead, she periodically transferred the growing cultures to a new dish to reduce the concentration of any original phosphorus to the point that any microbe making new DNA or other biomolecules would need to use the arsenic to survive.
------Science 3 December 2010