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The relevance of nanoscale biological fragments for ice nucleation in clouds.

O'Sullivan D, Murray BJ, Ross JF, Whale TF, Price HC, Atkinson JD, Umo NS, Webb ME - Sci Rep (2015)

Bottom Line: However, it is not clear that there are sufficient numbers of these particles in the atmosphere to strongly influence clouds.In addition, we quantify the ice-nucleating activity of nano-ice nucleating particles (nano-INPs) washed off pollen and also show that nano-INPs are present in a soil sample.Based on these results, we suggest that there is a reservoir of biological nano-INPs present in the environment which may, for example, become aerosolised in association with fertile soil dust particles.

View Article: PubMed Central - PubMed

Affiliation: Institute for Climate and Atmospheric Science, School of Earth &Environment, University of Leeds, UK.

ABSTRACT
Most studies of the role of biological entities as atmospheric ice-nucleating particles have focused on relatively rare supermicron particles such as bacterial cells, fungal spores and pollen grains. However, it is not clear that there are sufficient numbers of these particles in the atmosphere to strongly influence clouds. Here we show that the ice-nucleating activity of a fungus from the ubiquitous genus Fusarium is related to the presence of nanometre-scale particles which are far more numerous, and therefore potentially far more important for cloud glaciation than whole intact spores or hyphae. In addition, we quantify the ice-nucleating activity of nano-ice nucleating particles (nano-INPs) washed off pollen and also show that nano-INPs are present in a soil sample. Based on these results, we suggest that there is a reservoir of biological nano-INPs present in the environment which may, for example, become aerosolised in association with fertile soil dust particles.

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Ice nucleation activity of a sample of the fungus Fusarium avenaceum.The activity of the mycelium suspended in water is shown, along with the activities of the 0.2 μm, 1,000 kDa and 100 kDa filtrates. The number of active sites is normalized to the fresh mass of the whole fungus used to prepare the suspensions. Upon filtration through a 100 kDa filter the activity is found to drop below the baseline for the measurement, below which point nucleation events cannot be distinguished from nucleation by impurities in the Milli-Q® purified water. For clarity, representative error bars are only shown for a selection of data points.
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f2: Ice nucleation activity of a sample of the fungus Fusarium avenaceum.The activity of the mycelium suspended in water is shown, along with the activities of the 0.2 μm, 1,000 kDa and 100 kDa filtrates. The number of active sites is normalized to the fresh mass of the whole fungus used to prepare the suspensions. Upon filtration through a 100 kDa filter the activity is found to drop below the baseline for the measurement, below which point nucleation events cannot be distinguished from nucleation by impurities in the Milli-Q® purified water. For clarity, representative error bars are only shown for a selection of data points.

Mentions: By suspending known quantities of fungal (F. avenaceum) mycelium in microlitre-sized droplets and cooling them while monitoring for freezing events, we determined the cumulative number of active nucleation sites as a function of temperature (referred to as a cumulative nucleus spectrum). The number of active sites is reported per unit mass of the mycelium suspended in the droplets (see methods). To facilitate observation of ice nucleation at colder temperatures, experiments were also performed on suspensions which were serially diluted by factors of 100 and the results are shown in Figure 2. Droplets containing unfiltered fungal mycelium started to freeze at around −6°C. This indicates that F. avenaceum contains highly active INPs, consistent with previous reports1023. We also show the ice nucleation spectra for water droplets containing suspended mycelium which were subsequently passed through a sequence of filters. Heterogeneous ice nucleation at around −6°C continued to occur in the droplets following 0.2 μm filtration, consistent with Pouleur et al.10. Suspensions were then passed through a membrane filter with a molecular weight cutoff of 1000 kDa; this would correspond to a smooth spherical particle with a diameter (dsmooth sphere) of 13 nm for the average density of a typical protein (we take a protein density of 1.37 g cm−3 from Erickson24 who discuss the relationships between different metrics of protein size and shape). Surprisingly, these samples contained the same concentration of INPs as the 0.2 μm filtrate. When the filtrate was passed through a filter with a nominal molecular weight cut-off of 100 kDa (dsmooth sphere ~6 nm), the ice-nucleating activity was dramatically reduced, falling below the limit of detection for the assay determined by background freezing of the Milli-Q® purified water due to impurities (see methods). These results show that the INPs produced by F. avenaceum can function independently of fungal cells, are easy to remove from the parent fungus and are nanometre in scale.


The relevance of nanoscale biological fragments for ice nucleation in clouds.

O'Sullivan D, Murray BJ, Ross JF, Whale TF, Price HC, Atkinson JD, Umo NS, Webb ME - Sci Rep (2015)

Ice nucleation activity of a sample of the fungus Fusarium avenaceum.The activity of the mycelium suspended in water is shown, along with the activities of the 0.2 μm, 1,000 kDa and 100 kDa filtrates. The number of active sites is normalized to the fresh mass of the whole fungus used to prepare the suspensions. Upon filtration through a 100 kDa filter the activity is found to drop below the baseline for the measurement, below which point nucleation events cannot be distinguished from nucleation by impurities in the Milli-Q® purified water. For clarity, representative error bars are only shown for a selection of data points.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4308702&req=5

f2: Ice nucleation activity of a sample of the fungus Fusarium avenaceum.The activity of the mycelium suspended in water is shown, along with the activities of the 0.2 μm, 1,000 kDa and 100 kDa filtrates. The number of active sites is normalized to the fresh mass of the whole fungus used to prepare the suspensions. Upon filtration through a 100 kDa filter the activity is found to drop below the baseline for the measurement, below which point nucleation events cannot be distinguished from nucleation by impurities in the Milli-Q® purified water. For clarity, representative error bars are only shown for a selection of data points.
Mentions: By suspending known quantities of fungal (F. avenaceum) mycelium in microlitre-sized droplets and cooling them while monitoring for freezing events, we determined the cumulative number of active nucleation sites as a function of temperature (referred to as a cumulative nucleus spectrum). The number of active sites is reported per unit mass of the mycelium suspended in the droplets (see methods). To facilitate observation of ice nucleation at colder temperatures, experiments were also performed on suspensions which were serially diluted by factors of 100 and the results are shown in Figure 2. Droplets containing unfiltered fungal mycelium started to freeze at around −6°C. This indicates that F. avenaceum contains highly active INPs, consistent with previous reports1023. We also show the ice nucleation spectra for water droplets containing suspended mycelium which were subsequently passed through a sequence of filters. Heterogeneous ice nucleation at around −6°C continued to occur in the droplets following 0.2 μm filtration, consistent with Pouleur et al.10. Suspensions were then passed through a membrane filter with a molecular weight cutoff of 1000 kDa; this would correspond to a smooth spherical particle with a diameter (dsmooth sphere) of 13 nm for the average density of a typical protein (we take a protein density of 1.37 g cm−3 from Erickson24 who discuss the relationships between different metrics of protein size and shape). Surprisingly, these samples contained the same concentration of INPs as the 0.2 μm filtrate. When the filtrate was passed through a filter with a nominal molecular weight cut-off of 100 kDa (dsmooth sphere ~6 nm), the ice-nucleating activity was dramatically reduced, falling below the limit of detection for the assay determined by background freezing of the Milli-Q® purified water due to impurities (see methods). These results show that the INPs produced by F. avenaceum can function independently of fungal cells, are easy to remove from the parent fungus and are nanometre in scale.

Bottom Line: However, it is not clear that there are sufficient numbers of these particles in the atmosphere to strongly influence clouds.In addition, we quantify the ice-nucleating activity of nano-ice nucleating particles (nano-INPs) washed off pollen and also show that nano-INPs are present in a soil sample.Based on these results, we suggest that there is a reservoir of biological nano-INPs present in the environment which may, for example, become aerosolised in association with fertile soil dust particles.

View Article: PubMed Central - PubMed

Affiliation: Institute for Climate and Atmospheric Science, School of Earth &Environment, University of Leeds, UK.

ABSTRACT
Most studies of the role of biological entities as atmospheric ice-nucleating particles have focused on relatively rare supermicron particles such as bacterial cells, fungal spores and pollen grains. However, it is not clear that there are sufficient numbers of these particles in the atmosphere to strongly influence clouds. Here we show that the ice-nucleating activity of a fungus from the ubiquitous genus Fusarium is related to the presence of nanometre-scale particles which are far more numerous, and therefore potentially far more important for cloud glaciation than whole intact spores or hyphae. In addition, we quantify the ice-nucleating activity of nano-ice nucleating particles (nano-INPs) washed off pollen and also show that nano-INPs are present in a soil sample. Based on these results, we suggest that there is a reservoir of biological nano-INPs present in the environment which may, for example, become aerosolised in association with fertile soil dust particles.

Show MeSH