Macromolecular fungal ice nuclei in <i>Fusarium</i>: effects of physical and chemical processing

Abstract

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 coevolution of life and climate. Ice nucleation activity in fungi was first discovered in the cosmopolitan genus Fusarium, which is widespread in soil and plants, has been found in atmospheric aerosol and cloud water samples, and can be regarded as the best studied ice-nucleation-active (IN-active) fungus. The frequency and distribution of ice nucleation activity within Fusarium, however, remains elusive. Here, we tested more than 100 strains from 65 different Fusarium species for ice nucleation activity. In total, ∼11 % of all tested species included IN-active strains, and ∼16 % of all tested strains showed ice nucleation activity above −12 ∘C. Besides Fusarium species with known ice nucleation 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 indicate that cell-free ice-nucleating macromolecules (INMs) from Fusarium are smaller than 100 kDa and that molecular aggregates can be formed in solution. Long-term storage and freeze–thaw cycle experiments revealed that the fungal IN in aqueous solution remain active over several months and in the course of repeated freezing and thawing. Exposure to ozone and nitrogen dioxide at atmospherically relevant concentration levels also did not affect the ice nucleation activity. Heat treatments at 40 to 98 ∘C, however, strongly reduced the observed IN concentrations, confirming earlier hypotheses that the INM in Fusarium largely consists of a proteinaceous compound. The frequency and the wide distribution of ice nucleation activity within the genus Fusarium, combined with the stability of the IN under atmospherically relevant conditions, suggest a larger implication of fungal IN on Earth’s water cycle and climate than previously assumed.

The effect of biological particles and their ageing processes on aerosol radiative properties: Model sensitivity studies

“…Similarly, based on the measurements by Attard et al 2012, we derived values of 28°, 33°, and 44° for different types of bacteria. θ values for fungi based on the measurements by Kunert et al (2019) are similar (30°≤ θfungi ≤ 33°). Gute and Abbatt (2018) performed deposition freezing experiments of pollen; based on their experiments, we fitted θpollen = 15° for silver birch and θpollen = 16.3° for grey alder.…”

“…Based on these data, we calculated that the contact angle increased by ~1° after nitration for some bacteria. In contrast, Kunert et al (2019) reported 265 that protein nitration does not influence the cumulative fraction of IN for 65 species of fungi investigated.…”

“… Chemical transformations include oxidation (Jayaraman et al, 2008;Vaïtilingom et al, 2010), nitration (Franze et al, 2005), oligomerization (Tolocka et al, 2004), degradation of macromolecules (Estillore et 105 al., 2016), and changes of the protein conformations due to exposure to different pH values (Kristinsson and Hultin, 2004). These reactions lead to the modification of the protein structures and other macromolecules and thus affect BAP optical properties (Myhre et al, 2013), CCN activity (Sun and Ariya, 2006), and IN ability (Attard et al, 2012;Kunert et al, 2019).…”

Surfaces of Silver Birch (<i>Betula pendula</i>) are Sources of Biological Ice Nuclei: <i>In-vivo</i> and <i>In-situ</i> Investigations

“…Heterogeneous ice nucleation regarding biological organisms has been reported in plants (Diehl et al, 2001;Pummer et al, 2012), bacteria (Lindow et al, 1982;Wolber et al, 1986), fungi (Pouleur et al, 1992;Fröhlich-Nowoisky et al, 2015;Kunert et al, 2019;Iannone et al, 2011;Haga et al, 2013), moss spores (Weber, 2016), and lichen (Kieft, 1988). Plants growing in temperate environments use mechanisms such as extracellular freezing (Burke et al, 1976;Storey and Storey, 2005;Pearce, 2001) or extra-organ freezing (Quamme, 1978;Ishikawa and Sakai, 1981) to survive sub-zero temperatures.…”

“…(Pummer et al, 2012;Diehl et al, 2001). Past studies showed that INPs from biological systems are rather in a macromolecular size range (ice-nucleating macromolecules, INM) (Pummer et al, 2012;Kunert et al, 2019). If those INMs can be easily washed off a plant's surface, they would have the potential to become aerosolized and serve as an important source for INPs in the atmosphere.…”