Macromolecular fungal ice nuclei in Fusarium: effects of physical and chemical processing

Authors: KUNERT, ANNA - Max Planck Institute For Chemistry; POHLKER, MIRA - Max Planck Institute For Chemistry; KREVERT, CAROLA - Max Planck Institute For Chemistry; WIEDER, CARSTEN - Max Planck Institute For Chemistry; SPETH, KAI - Max Planck Institute For Chemistry; Hanson, Linda; MORRIS, CINDY - Institut National De La Recherche Agronomique (INRA); SCHMALE, DAVID - Virginia Tech; POSCHL, ULRICH - Max Planck Institute For Chemistry; FROHLICH-NOWOISKY, JANINE - Max Planck Institute For Chemistry

Submitted to: Biogeosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2019
Publication Date: 12/9/2019
Citation: Kunert, A.T., Pohlker, M.L., Krevert, C.S., Wieder, C., Speth, K.R., Hanson, L.E., Morris, C., Schmale, D.G., Poschl, U., Frohlich-Nowoisky, J. 2019. Macromolecular fungal ice nuclei in Fusarium: effects of physical and chemical processing. Biogeosciences. 16:4647–4659. https://doi.org/10.5194/bg-16-4647-2019.
DOI: https://doi.org/10.5194/bg-16-4647-2019

Interpretive Summary: Some biological particles can function as ice nuclei (IN), triggering ice formation at higher temperatures than occurs for pure water. The impact of such biological particles on formation of clouds and precipitation (rain and snow) is still poorly understood and is a major gap in the scientific understanding of the influence of living organisms on climate. We tested for IN activity in the widespread fungal genus Fusarium, testing over 100 strains from 65 different species. From these, approximately 11% of the species tested had IN activity, with 16% of all strains showing IN. Three of these species were newly identified to have IN activity. The IN activity per gram of tissue for all tested Fusarium species was similar to other biological IN from fungi, and a commercial IN product. The IN activity was determined to be small and stable through storage, multiple freeze-thaw cycles, and other reactions typical of atmospheric aging. The frequency of Fusarium species in diverse environments and the distribution of IN activity within this genus, combined with the stability of this IN activity, indicate a potential for a significant impact of such fungal IN on the Earth’s water cycle.

Technical 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-active) strains, and ~16% of all tested strains showed IN activity above -14°C. Besides Fusarium species with known IN activity, F. armeniacum, F. begonia, 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 Snowmax®. Filtration experiments indicate 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 that the Fusarium IN remains active in solution for several months and after repeated freezing and thawing. Oxidation and nitration reactions, as occur during atmospheric aging, did not affect the activity of the Fusarium IN. The high frequency of Fusarium species and the wide distribution of IN activity within the genus, combined with the high stability of the IN, indicate the potential for a significant impact of fungal IN on the Earth’s water cycle and climate.