NASA researcher Felisia Wolfe-Simon reported today that her team found a bacteria, called GFAJ-1, in Mono Lake, California that is unlike any other known form of life on earth.
GFAJ-1 uses arsenic (which is poisonous to almost every other creature) instead of phosphorous in its DNA, RNA, proteins, and cell membrane.
This is a spectacular finding as it challenges our understanding of the tree of life as we knew it. Before the discovery of GFAJ-1, every organism on earth was connected to each other by using the same chemical building blocks to build DNA and RNA (forming a lineage of shared common ancestors).
The researchers conceded that the odd bacteria, in and of themselves, don't prove yet that there is a fundamentally different basis for life on Earth. "It is beginning to open the door a crack to possibilities," Ms. Wolfe-Simon said.
Several independent experts noted that these unusual organisms weren't so far out of the ordinary and that there might be more organisms to be found on earth that can use alternative chemical substances as building blocks. Some researchers critiqued the methodology of the study (see article here): The NASA researchers grew the bacteria in a broth of nutrients. When they gradually reduced the supply of phosphate and added arsenate, the bacteria still managed to grow. The scientists examined the DNA and inferred that it contained arsenic. There might be several flaws in that method: First, when the NASA scientists removed and washed the DNA, arsenic could still have stuck to the DNA without having been integrated. Second, the NASA scientists were feeding the bacteria salts which they freely admit were contaminated with a tiny amount of phosphate. It's possible, the critics argue, that the bacteria eked out a living on that scarce supply.
Future studies will show if these bacteria really used arsenic instead of phosphate. Many researchers did not rule out the possibility of arsenic-based lifeforms, but more thorough studies are needed.