Subsisting on Arsenic, a Microbe May Redefine Life

THE NEW YORK TIMES:
Scientists said Thursday that they had trained a bacterium to eat and grow on a diet of arsenic, in place of phosphorus — one of six elements considered essential for life — opening up the possibility that organisms could exist elsewhere in the universe or even here on Earth using biochemical powers we have not yet dared to dream about.

...The results could have a major impact on space missions to Mars and elsewhere looking for life. The experiments on such missions are designed to ferret out the handful of chemical elements and reactions that have been known to characterize life on Earth. The Viking landers that failed to find life on Mars in 1976, Dr. Wolfe-Simon pointed out, were designed before the discovery of tube worms and other weird life in undersea vents and the dry valleys of Antarctica revolutionized ideas about the evolution of life on Earth.