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Biological Chemistry

Making ice microbe-style

Bacterial proteins found to seed ice formation above freezing temperatures by helping to arrange water molecules

by Sarah Everts
April 25, 2016 | A version of this story appeared in Volume 94, Issue 17

The plant pathogen Pseudomonas syringae attacks its victims by seeding the formation of ice on leaves, even before temperatures fall below freezing. This ice formation bursts plant cells, giving the pathogen a route into its host. The bacterium’s skills are put to constructive use by ski resorts and desperate Winter Olympics hosts who use the microbe to help make snow. Although researchers know that the bacteria nucleate ice using proteins embedded in their membrane, not much is known about exactly how this occurs, in part because the 1,200-amino-acid proteins have not succumbed to X-ray crystallography and other structural biology characterization. A research team led by Tobias Weidner of the Max Planck Institute for Polymer Research now proposes that the bacterial proteins nucleate ice by controlling the order and dynamics of water molecules (Sci. Adv. 2016, DOI: 10.1126/sciadv.1501630). With computer simulations and sum frequency generation spectroscopy, an analytical method used to study surfaces and interfaces, the team showed that P. syringae proteins contain repeating hydrophilic and hydrophobic patterns that likely help arrange water molecules to enhance ice nucleation. They found the bacterial machinery can also remove heat from nearby water molecules, which can amplify the effect.


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