Pseudomonas syringage is known for its ice nucleating properties — promoting freezing of the water molecules. It acts as a seed, around which water molecules can arrange themselves in a way which lets them crystalize at a relatively high temperature of -2ÂșC.
It is a biological near-counterpart to Vonnegut’s Ice-nine, a substance – invented in his “Cat’s Cradle” – which promotes ice nucleation at room temperature.

Here’s the excerpt from Cat’s Cradle talking about Ice-nine (one of the best explanations of ice nucleation):

“There are several ways,” Dr. Breed said to me, “in which certain liquids can crystallize–can freeze–several ways in which their atoms can stack and lock in an orderly, rigid way.”
That old man with spotted hands invited me to think of the several ways in which cannonballs might be stacked on a courthouse lawn, of the several ways in which oranges might be packed into a crate. “So it is with atoms in crystals, too; and two different crystals of the same substance can have quite different physical properties.” He told me about a factory that had been growing big crystals of ethylene diamine tartrate. The crystals were useful in certain manufacturing operations, he said. But one day the factory discovered that the crystals it was growing no longer had the properties desired. The atoms had begun to stack and lock–to freeze–in different fashion. The liquid that was crystallizing hadn’t changed, but the crystals it was forming were, as far as industrial applications went, pure junk.

How this had come about was a mystery. The theoretical villain, however, was what Dr. Breed called “a seed.” He meant by that a tiny grain of the undesired crystal pattern. The seed, which had come from God-only-knows-where, taught the atoms the novel way in which to stack and lock, to crystallize, to freeze.
“Now think about cannonballs on a courthouse lawn or about oranges in a crate again,” he suggested. And he helped me to see that the pattern of the bottom layers of cannonballs or of oranges determined how each subsequent layer would stack and lock. “The bottom layer is the seed of how every cannonball or every orange that comes after is going to behave, even to an infinite number of cannonballs or oranges.”

“Now suppose,” chortled Dr. Breed, enjoying himself, “that there were many possible ways in which water could crystallize, could freeze. Suppose that the sort of ice we skate upon and put into highballs–what we might call ice-one–is only one of several types of ice. Suppose water always froze as ice-one on Earth because it had never had a seed to teach it how to form ice-two, icethree, ice-four…? And suppose,” he rapped on his desk with his old hand again, “that there were one form, which we will call ice-nine–a crystal as hard as this desk–with a melting point of, let us say, one-hundred degrees Fahrenheit, or, better still, a melting point of one-hundred-and-thirty degrees.”

There he said to me, “Where were we? Oh yes!” And that old man asked me to think of United States Marines in a Godforsaken swamp.
“Their trucks and tanks and howitzers are wallowing,” he complained, “sinking in stinking miasma and ooze.” He raised a finger and winked at me. “But suppose, young man, that one Marine had with him a tiny capsule containing a seed of ice-nine, a new way for the atoms of water to stack and lock, to freeze. If that Marine threw that Seed into the nearest puddle…?”
“The puddle would freeze?” I guessed.
“And all the muck around the puddle?”
“It would freeze?”
“And all the puddles in the frozen muck?”
“They would freeze?”
“And the pools and the streams in the frozen muck?”
“They would freeze?”
“You bet they would!” he cried. “And the United States Marines would rise from the swamp and march on!”

more ice-nice excerpts are here