The bacteria known as Geobacter sulfurreducens, when exposed to uranium, pretty much just die. But under certain conditions, they can grow appendages that can literally make uranium drop out of water like a stone. Scientists have found a way to get them to grow the right way, and may even be able to recreate them artificially.
Bacteria are very misunderstood organisms. Usually we only pay attention to them when they hide on spinach in an attempt kill us. Occasionally we thank them for helping us digest food or keep our skin from letting in viruses. But it may be time to really pay attention, because one species can drop uranium straight out of water. Geobacter sulfurreducens are little bacteria that produce electrons as part of their metabolism. The bacterium needs to jettison these electrons quickly, and so it shoves them off onto anything it can force them onto.
One of the objects onto which the bacteria tend to dump the electrons is uranium atoms. These atoms are soluble in water, meaning that they can dissolve in groundwater, sea water, and drinking water. The atom goes wherever the water goes, including into the bodies of people. It does this because it weakly interacts with water through the quantity and placement of its protons and electrons. When the bacteria dumps its extra electron on the uranium atom, it disrupts this interaction by changing the atom's charge. The uranium is no longer interacting with the water and 'precipitates' - drops out of the water and down to the ocean (or lake, or river) floor.
The bacterium generally doesn't come out of this interaction well. It has to absorb the uranium atom into its body in order to transfer the electron, and in ingesting the atom it poisons itself. Under certain conditions, though, the bacteria grow 'hair'. The tiny hairs, called pili, serve as small wires that conduct the electron out of the bacterium's body and into the uranium atom. The uranium isn't absorbed, the electron is transferred efficiently, the bacterium lives, and the uranium ends up on the ground.
These appendages let the bacteria live long happy lives while taking out uranium atoms like they're extras in a James Bond movie. It was thought that these bacteria would be useful in helping purify water, especially after spills at nuclear plants. Up until recently, Geobacter sulfurreducens has stubbornly refused to grow hair in the lab. After some testing, lab technicians realized they were making life too easy on the bacteria. Lab conditions are meant to help bacteria thrive all on their own, so extra hair growth was a wasted expenditure of energy. The researchers dropped the temperature of the Geobacter sulfurreducens samples, the bacteria obligingly grew a heavy pelt. The researchers were able to measure the amount of uranium precipitated, and hopes are high to use bugs, or even non-organic robo-bugs, to take out future hazardous material spills.
Via Scientific American.