The protein secretion of the sea ice diatom enables growth in freezing temperatures by inhibiting the recrystallization of the surrounding ice crystals.

Sea ice diatoms are single-celled algae that live in extremely cold, aquatic environments, including Arctic and Antarctic sea ice. In these harsh environments, they have developed mechanisms to protect themselves against the extremes of temperature, salinity, and light. One such mechanism is extracellular ice-binding protein.
Extracellular ice-binding proteins, excreted by sea ice diatoms, align themselves with and bind to the small, growing ice crystals just outside of the sea ice diatom’s protective outer layer. While the exact binding mechanism is unknown, it is believed that the ice-binding proteins act as complementary pieces to ice crystals in a three-dimensional jigsaw puzzle. The ice-binding proteins lock the small ice crystals in place, thereby preventing them from rearranging into a larger ice crystal. This rearrangement of small ice crystals into a larger one (known as ice recrystallization) occurs spontaneously and is a natural part of ice crystal growth.

Ice recrystallization is one of the primary mechanisms of cell death in freezing temperatures. While the small ice crystals can exist at the surface of cells without causing cell death, large ice crystals cannot. Large ice crystals, formed when the adjacent small ice crystals join together and align themselves in the same direction, act as knives to the cells. The large ice crystals are powerful enough to force their way in between cells and puncture the cells’ protective outer layer. The insides of the cells, when exposed to freezing temperatures, die. The extracellular ice-binding proteins prevent the large ice crystals from forming, and are thus essential for the growth and survival of sea ice diatoms embedded in ice.

This summary was contributed by Jennifer Lawrence.

References

"One factor that may contribute to survival is the release by the diatoms of exopolymeric substances that can help to preserve a liquid environment as sea ice freezes. We have been investigating another potential survival mechanism that involves the production of proteins that have an affinity for ice crystals. Associated with the diatom community are extracellular proteins (formerly called ice-active substances) that strongly interact with ice. The most conspicuous effect of these proteins is to cause pitting and other deformities on the surface of growing ice crystals, which is a sign of adsorption of an impurity to a crystal surface." (Janech et al. 2006:410)

"We show that the IBPs have strong effects on inhibiting the recrystallization of ice and on retaining brine in ice. Both these properties help preserve a liquid environment in ice, which is considered essential for survival for microbes embedded in ice." (Raymond et al. 2009:130)

"Diatom IBPs resemble plant antifreezes in that they do not appreciably lower the freezing point, which suggests that they mainly function as cryoprotectants." (Janech et al. 2006:410)

“Ice recrystallization (IR) is a process in which large ice crystals grow at the expense of smaller ones.  It occurs constantly in nature...in conditions of moderate cooling of a partially frozen environment or at accelerated rate due to temperature fluctuations of frozen substances...Recrystallization...damages the cells and tissues due to membrane rupture and cell dehydration, reducing the survival rates.  Organisms inhabiting cold environments and prone to IR injuries, such as...[sea ice diatoms], have developed...ice binding proteins which interact with ice for various biological purposes.  The [ice binding proteins] adsorb to ice surfaces and restrict the growth of ice to the areas between bound protein molecules.  Such proteins were shown to block IR effectively...and may serve as additives in many applications in which ice recrystallization is an obstacle.  Although ice recrystallization inhibition (IRI) activity of a variety of [ice binding proteins] was studied...the mechanisms by which [ice binding proteins] inhibit IR is unknown.” (Zalis 2013)

Journal article
ICE-BINDING PROTEINS FROM SEA ICE DIATOMS (BACILLARIOPHYCEAE)1Journal of PhycologyMarch 4, 2006
Michael G. Janech, Andreas Krell, Thomas Mock, Jae-Shin Kang, James A. Raymond

Journal article
NOVEL ICE-BINDING PROTEINS FROM A PSYCHROPHILIC ANTARCTIC ALGA (CHLAMYDOMONADACEAE, CHLOROPHYCEAE)Journal of PhycologyMarch 2, 2009
James A. Raymond, Michael G. Janech, Christian H. Fritsen

Book section
Ice Recrystallization Inhibitors: From Biological Antifreezes to Small Molecules

Journal article
Ice binding, recrystallization inhibition, and cryoprotective properties of ice-active substances associated with Antarctic sea ice diatomsCryobiologyJuly 4, 2003
James A. Raymond, Charles A. Knight

Journal article
142 Ice growth in the presence of an antifreeze proteinCryobiologyMay 29, 2017
Maddalena Bayer-Giraldi, Ilka Weikusat, Cornelia Isert

Living System/s

Organism
DiatomaceaeSpecies