Articles | Volume 16, issue 12
Research article
29 Jun 2016
Research article |  | 29 Jun 2016

The adsorption of fungal ice-nucleating proteins on mineral dusts: a terrestrial reservoir of atmospheric ice-nucleating particles

Daniel O'Sullivan, Benjamin J. Murray, James F. Ross, and Michael E. Webb

Abstract. The occurrence of ice-nucleating particles (INPs) in our atmosphere has a profound impact on the properties and lifetime of supercooled clouds. To date, the identities, sources and abundances of particles capable of nucleating ice at relatively low supercoolings (T  >  −15 °C) remain enigmatic. While biomolecules such as proteins and carbohydrates have been implicated as important high-temperature INPs, the lack of knowledge on the environmental fates of these species makes it difficult to assess their potential atmospheric impacts. Here we show that such nanoscale ice-nucleating proteins from a common soil-borne fungus (Fusarium avenaceum) preferentially bind to and confer their ice-nucleating properties to kaolinite. The ice-nucleating activity of the proteinaceous INPs is unaffected by adsorption to the clay, and once bound the proteins do not readily desorb, retaining much of the activity even after multiple washings with pure water. The atmospheric implications of the finding that biological residues can confer their ice-nucleating ability to dust particles are discussed.

Short summary
In the absence of particles which can trigger freezing, cloud droplets can exist in a supercooled liquid state well below the melting point. However, the sources of efficient ice-nucleating particles in the atmosphere are uncertain. Here we show that ice-nucleating proteins produced by soil fungi can bind to clay particles in soils. Hence, the subsequent dispersion of soil particles into the atmosphere acts as a route through which biological ice nucleators can influence clouds.
Final-revised paper