Highly active and stable fungal ice nuclei are widespread among <i>Fusarium</i> species

Abstract

Some biological particles and macromolecules are particularly efficient ice nuclei (IN), triggering ice formation at temperatures close to 0 • C. The impact of biological particles on cloud glaciation and the formation of precipitation is still poorly understood and constitutes a large gap in the scientific understanding of the interactions and co-evolution of life and climate. To investigate the frequency and distribution of IN activity within the fungal genus Fusarium, more than 100 strains from 65 different Fusarium species were screened. In total, ∼11 % of all tested species included ice nucleation-active (IN-5 active) strains, and ∼16 % of all tested strains showed IN activity above -14 • C. Besides Fusarium species with known IN activity, F. armeniacum, F. begoniae, F. concentricum, and F. langsethiae were newly identified as IN-active. The cumulative number of IN per gram of mycelium for all tested Fusarium species was comparable to other biological IN like Sarocladium implicatum, Mortierella alpina, and Snomax ® . Filtration experiments suggest that the single cell-free Fusarium IN is smaller than 100 kDa, and that aggregates can be formed in solution. Long-term storage and freeze-thaw cycle experiments revealed 10 that the Fusarium IN remain active in solution for several months and after repeated freezing and thawing. Oxidation and nitration reactions, as occurring during atmospheric aging, did not affect the activity of the Fusarium IN. The high frequency of Fusarium and the wide distribution of IN activity within the genus, combined with the high stability of the IN, suggest a significant impact of fungal IN on the Earth's water cycle and climate.

Lignin's ability to nucleate ice via immersion freezing and its stability towards physicochemical treatments and atmospheric processing

“…Thus, atmospheric processing by O3 likely does not influence lignin's IN activity. This stability in IN activity after oxidative treatments with O3 up to 1 ppm and 6 h duration was also observed by Kunert et al (2019) and Attard et al (2012) who investigated fungal and bacterial ice nuclei, respectively. Notably, the oxidative gas mixtures in both these studies contained additionally nitrogen dioxide (NO2) as a second oxidant in the same concentration as O3.…”

“…Atmospheric processing causes aging in the aerosols, altering its physical and chemical properties. The changes may subsequently have an impact on their IN activity (Attard et al, 2012;Borduas-Dedekind et al, 2019;Gute and Abbatt, 2018;Kunert et al, 2019). To observe possible impacts of atmospheric processing on lignin's IN activity, we conducted photochemical experiments and reactions with ozone.…”

Electrostatic Interactions Control the Functionality of Bacterial Ice Nucleators

“…Ice formation is the most important liquid-to-solid phase transition on earth and is strongly affected by the presence of nucleators that initiate heterogeneous ice nucleation at temperatures above −40 °C. There is a large variety of compounds that can act as ice nucleators, and their efficiency strongly differs. − The most efficient ice nucleators are bacteria from Pseudomonas syringae, which can initiate the crystallization of water at temperatures as high as −2 °C. , The ability of bacteria to nucleate ice is caused by specialized ice-nucleating proteins (INPs) that are anchored in the outer membrane on the bacterial cell wall . Bacterial INPs contain a large central-repeat domain that has been proposed to be the active site and which is responsible for ice nucleation through a mechanism that likely involves the preordering of water. , Apart from the specific ice-binding site, the high ice nucleation activity of INPs has been shown to depend on the size of the nucleation size and the ability to aggregate into larger protein clusters. − INPs have repeatedly been shown to aggregate in the bacterial outer membranes, ,,− and both the number of INPs in the aggregate and the sub-angstrom distance between the INPs affect the ice nucleation efficiency .…”