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Abstract:
Ice-nucleating organisms play important roles in the environment. With their ability to induce ice formation at temperatures just below the ice melting point, bacteria such as
Pseudomonas syringae attack plants through
frost damage using specialized e-nucleating proteins. Besides the impact on agriculture and microbial ecology, airborne P. syringae
can affect atmospheric glaciation processes, with consequences for cloud evolution, precipitation, and climate. Biogenic ice nucleation is also relevant for artificial snow production and for biomimetic materials for controlled interfacial freezing. We use interface-specific sum frequency generation (SFG) spectroscopy to show that hydrogen bonding at the water-bacteria contact imposes structural ordering on the adjacent water network. Experimental SFG data and molecular dynamics simulations demonstrate that ice-active sites within P. syringae feature unique hydrophilic-hydrophobic patterns to enhance ice nucleation.
The freezing transition is further facilitated by the highly effective removal of latent heat from the nucleation
site, as apparent from time-resolved SFG spectroscopy.
