Like the Marvel Comics superhero Iceman, some bacteria have harnessed frozen water as a weapon. Species such as Pseudomonas syringae have special proteins embedded in their outer membranes that help ice crystals form, and they use them to trigger frost formation at warmer than normal temperatures on plants, later invading through the damaged tissue. When the bacteria die, many of the proteins are wafted up into the atmosphere, where they can alter the weather by seeding clouds and precipitation.
Now scientists from Germany have observed for the first time the step-by-step, microscopic-level action of P. syringae's ice-nucleating proteins locking water molecules in place to form ice. The team will present their findings at the AVS 60th International Symposium and Exhibition, held Oct. 27 Nov. 1 in Long Beach, Calif.
"Ice nucleating proteins are the most effective ice nucleators known," said Tobias Weidner, leader of the surface protein group at the Max Planck Institute for Polymer Research. The proteins jump-start the process of ice crystal formation so well that dried ice-nucleating bacteria are often used as additives in snowmakers.
Although scientists discovered ice-nucleating proteins decades ago, little is known about how they actually work. Weidner and his team tackled the mystery with a powerful tool called spectroscopy that can decipher patterns in the interaction between light and matter to visualize the freezing process in layers of materials only a few molecules thick.
The researchers prepared a sample of fragments of P. syringae bacteria that they spread over water to form a surface film. As the temperature was lowered from room temperature to near freezing levels the scientists probed the interface between the bacterial proteins and the water with two laser beams. The beams combined within the sample and a single beam was emitted back, carrying with it information about how the protein and
|Contact: Catherine Meyers|
American Institute of Physics