Six elements are known to be necessary for life: carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus. It may be time to a new one to the list: arsenic. At least, thats the case for a strain of bacteria called GFAJ-1 isolated from California’s Mono Lake. This unique bacteria species is able to use arsenic in place of phosphorus in its cell parts.
Mono Lake, an isolated body of water located in California’s eastern Sierras, is one of the oldest lakes in North America. Its waters are both alkaline–at a pH of 10–and very salty. The lakes waters are also rich in arsenic. Previous research at the lake indicated that photosynthetic bacteria were able to use arsenic to fuel the processes of photosynthesis and respiration. This finding made scientists wonder if perhaps arsenic played an even more important role in the life functions of these bacteria.
In their study, the scientists grew the bacteria in a lab setting on a diet rich in arsenic and low in phosphorus. They discovered that as the amount of phosphorus became more and more diluted–to the point where it was no longer present–the microbes continued to grow. In fact, the microbes grown in arsenic grew about 60 percent larger in size than microbes grown in phosphorus. However, much of the enlarged cell was made up of large, empty internal spaces.
In their experiment, the researchers used a slightly radioactive form of arsenic in order to track where it ended up in the cell. They found that the bacteria were able to use arsenic in place of phosphorus to build proteins, DNA, and ATP. Then again, the scientists also noted that the bacteria actually do have phosphorus in their DNA and additionally tend to grow better in the presence of phosphorus; its just that when push comes to shove, the bacteria are able to use arsenic as a replacement for phosphorus when absolutely necessary to survive.
This research has implications for a number of fields including evolutionary biology, organic chemistry, microbiology, and biochemistry, just to name a few. The results of this research raise a number of questions that the scientists are enthusiastic about pursuing, especially with regard to how arsenic is able to take the place of and apparently perform the function of phosphorus in these bacteria cells.
Collaboration was key to this research and included scientists from Arizona State University, Duquesne University, Lawrence Livermore National Lab, Stanford Synchotron Radiation Lightsource, United States Geological Survey (USGS), and the University of Pittsburgh. NASAs Astrobiology Program provided a significant amount of funding for this research.