Ice-nucleation (IN) at temperatures way higher than −42 °C is part of our daily perception but only possible due to the interaction with particles, which serve as nuclei. Among the most relevant ice-nucleating agents are mineral dusts as well as biological macromolecules. While the IN efficiencies of many of these substances have been quantified by freezing assays, the molecular level interactions between their surfaces and the adjacent water molecules are still not fully understood. Here we focus on the bacterium Pseudomonas syringae, a plant pathogen, which uses its outstanding IN efficiency to cause frost damage to plants and to capture nutrients, and on IN active fungi species showing similar efficiencies. The impact of such a variety of ice-active microorganisms is not limited to agriculture hence they appear as airborne particles and are contributory factors to atmospheric glaciation processes. We study the temperature dependent alignment of water adjacent to the biomolecules using sum-frequency generation vibrational spectroscopy (SFG). Previous studies showed, that commercially available P. syringae (Snomax®) in heavy water increasingly order the interfacial D2O-molecules when the solution is cooled down. The result indicates that the bacterium’s ability to order water is optimized to be enhanced at temperatures close to the freezing point. Here we demonstrate that the effect also occurs in the natural H2O environment. Moreover, we generalize the result by verifying them for two further IN-active fungi: Fusarium acuminatum, another IN active plant pathogen with enormous impact on European and American agriculture and Alpina mortierella, which is widely spread in soils.

Ice-nucleating bacteria and fungi: Increased order of water molecules at low temperatures

2019 Fall National Meeting

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