Scientists Uncover Frozen Tricks Behind Ice-Seeding Bacteria

Some bacteria can harness frozen water as a weapon, using special proteins embedded in their outer membranes to help ice crystals form. Triggering frost formation, the bacteria then invades through the damaged tissues of plants. Now, scientists have observed this bacteria's ability for the first time, step-by-step, at a microscopic level. This could reveal new insights into ice crystal formation.

The bacteria in question are Pseudomonas syringae. In fact, dried ice-nucleating bacteria like these are often used as additives in snowmakers. Yet when these bacteria die, many of the proteins are wafted up into the atmosphere where they can alter the weather by seeding clouds and precipitation.

Although scientists discovered ice-nucleating proteins decades ago, still very little is known about how they actually work. In order to learn a bit more about them, the researchers employed spectroscopy in order to decipher patterns in the interaction between light and matter in order to visualize the freezing process in layers of materials only a few molecules thick.

More specifically, 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 then probed the interface between the bacterial proteins and the water with two laser beams.

So what did they find? As the temperatures approached freezing, the water molecules at the ice-nucleating protein surface suddenly became more ordered and the molecular motions more sluggish. They also found that thermal energy was very quickly removed from the surrounding water. This seemed to show that the protein has a specific mechanism for heat removal.

"We were very surprised by these results," said Tobias Weidner, one of the researchers, in a news release. "When we first saw the dramatic increase of water order with lower temperatures we believed it was an artifact."

These proteins are some of the most effective promoters of ice particle formation, so understanding what happens at a molecular level is important for future research. In fact, these proteins have the potential to significantly influence weather patterns. Learning a bit more about this bacteria triggers frost could allow scientists to understand how ice particle formation occurs in the upper atmosphere.

The findings will be presented at the AVS 60^th International Symposium & Exhibition in California.