July's Paper of the Month

A hexagonal ice crystal in the presence of birch pollen molecules. The shape is indicative of ice crystal growth inhibition.

A hexagonal ice crystal in the presence of birch pollen molecules. The shape is indicative of ice crystal growth inhibition.

Ice crystal growth through nucleation is an important natural process for atmospheric and cryobiological processes. For biological organisms, surviving sub-freezing temperatures requires tackling intracellular ice formation. Such organisms have evolved antifreeze proteins to inhibit ice crystal growth, thus preserving structural integrity. 

Ice crystals are formed in clouds triggered by ice nucleating particles. Originally it was believed these particles were forms of mineral dust but recent studies have found them to also include biological agents including pollen, bacteria, fungal spores, cellulose and microalgae. 

Active sites are regions on the ice nucleating particles where critical ice embryo formation occurs. These can be proteins or polysaccharides in the cell membrane although studies have found these are still active when separated from their original particles. 

Yet these biological molecules can act as both ice nucleators and ice inhibitors and consequently there has been much desire to further understand the manner in which these molecules interact with ice. The search for such answers may also help to further explain how biological organisms survive extreme climatic conditions.

July’s Paper of the Month comes from the Bielefeld University. They tested for the presence of antifreeze molecules in various types of known ice nucleating boreal pollen. The group conducted their temperature controlled experiment using the Linkam BCS196.

FTIR spectroscopy of the pollen highlighted two polysaccharides with similar chemical structures which differed in size. The larger (>100kD) of the two was responsible for the ice nucleating ability of the pollen while the smaller (<100kD) exhibited ice inhibiting abilities. 
Analysis of IR spectrum suggests the ice inhibiting molecules are either fragments of ice nucleating molecules, or ice nucleating molecules are clusters of smaller ice inhibiting molecules. The group’s results indicate both to have similar molecular moieties. Complementary findings in studies on boreal pollen suggest this may be a mechanism to protect pollen against springtime frosts. 

When asked about the role of the BCS196 stage, Professor Koop said: “For the ice growth inhibition experiments, we have developed an assay which makes use of the BCS196 stage while attached to a brightfield transmission optical microscope. The stage allows for a rapid cooling to about -50 °C in order to produce a film of polycrystalline ice and, subsequently, an accurate and constant hold temperature at -8 °C, during which we determine how the size of the ice crystals changes over several hours and how this is affected by the pollen molecules.”

Their valuable work better helps us to understand the way molecules may be interacting with ice in natural processes. 

By Tabassum Mujtaba

Dreischmeier, K. et al. Boreal pollen contain ice-nucleating as well as ice-binding ‘antifreeze’ polysaccharides. Sci. Rep. 7, 41890; doi: 10.1038/srep41890 (2017).