Two new reports show that a bacterium, known as GFAJ-1, requires small amounts of phosphate to grow—and that it cannot substitute arsenic for phosphorus to survive, as a 2010 report in Science had suggested.

The GFAJ-1 bacterium, which was discovered in the arsenic-rich sediments of California’s Mono Lake, became the center of a controversy last year after Felisa Wolfe-Simon of the NASA Astrobiology Institute and the U.S. Geological Survey and colleagues reported that the microorganism could incorporate arsenic into its DNA when phosphorus wasn’t available.

In a study published online at Science Express on 2 December 2010, Felisa Wolfe-Simon and colleagues described a bacterium from Mono Lake, California, which they claimed substitutes arsenic for a small amount of the phosphorus in its DNA and other molecules. If true, this finding would raise important questions about life’s basic requirements, since only six elements—carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus—make up the bulk of living matter.

Researchers have discovered a bacterium that can live and grow off arsenic, a new study reports. The findings point for the first time to a microorganism that is able to use a toxic chemical (rather than the usual phosphate) to sustain growth and life.

The study is being published online 2 December at the ScienceExpress Web site.