Scientists have found the first known living organism that incorporates arsenic into the working parts of its cells. What's more, the arsenic replaces phosphorus, an element long thought essential for life. Staff scientist Sam Webb led the research undertaken at the Stanford Synchrotron Radiation Lightsource located at SLAC National Accelerator Laboratory.
The latest discovery is all about a bacterium – strain GFAJ-1 of the Halomonadaceae family of Gammaproteobacteria – scooped from sediments of eastern California's Mono Lake, which is extremely salty with naturally high levels of arsenic. In the laboratory, the researchers successfully grew microbes from the lake on a diet that was very lean on phosphorus, but included generous helpings of arsenic. Key issues that the researchers needed to address were the levels of arsenic and phosphorus in the experiments and whether arsenic actually became incorporated into the organisms' vital biochemical machinery, such as DNA, proteins and the cell membranes. A variety of sophisticated laboratory techniques was used to nail down where the arsenic went, including mass spectrometry measurements by Gordon at the W.M. Keck Foundation Laboratory for Environmental Biogeochemistry at ASU. Commenting on the significance of the discovery, Davies says: “This organism has dual capability. It can grow with either phosphorous or arsenic. That makes it very peculiar, though it falls short of being some form of truly 'alien' life belonging to a different tree of life with a separate origin. However, GFAJ-1 may be a pointer to even weirder organisms. The holy grail would be a microbe that contained no phosphorus at all.”