Imagine you fell asleep now and woke up again 250 million years later. Science fiction? In fact, it might be possible for bacteria. Researchers from Pennsylvania and Texas claim to have revived such ancient organisms from a salt crystal, pushing the age for the oldest living creature back at least twofold. As the three scientists report in this weeks Nature,the validity of their assertion rests on two conditions: proving the age of the salt crystal and demonstrating that the bacteria are actually from within crystal, not the environment.
The salt crystals they examined came from the Waste Isolation Pilot Plant (right). Certain features of the crystals indicated they had not recrystallized since Salado formed, suggesting they could be as old. And the researchers rejected any crystals that seemed damaged, trying to avoid the chance that any bacteria had leaked in through cracks over the millennia. They then went to a lot of trouble to make sure no bacteria from the outside world could contaminate the crystals before their analysis: they washed the crystals with a strong base and acid, and sterilized all equipment. When they poured liquid collected from a crystal inclusion into a bacterial culture medium, they found a bacterium of the Bacillusvariety.
Under unfavorable environmental conditions, these bacteria are known to enter durable states in which they are called spores--and so it is conceivable that in this part of their life cycle, the bacteria might be able to survive much longer than is normal. A comparison of an RNA sequence from the bacterium with that of other bacteria showed that its closest cousin is a species called Bacillus marismortui;the two are 99 percent identical in that gene. The case these authors make seems convincing, but they haven't solved what is perhaps the biggest mystery about the bacteria: How on earth (and in salt) did they survive for so long and why don't they differ more from present day bacterium?