A significant key to the success and versatility of the notothenioids is their ability to resist becoming frozen at very low temperatures. This is in large part due to their production of antifreeze proteins, which inhibit the growth of ice crystals in their bodily fluids. Professor DeVries tells Scientia of the importance of this adaptation for biodiversity in the region: ‘If it were not for the capability of polar fishes to avoid freezing – as a result of the presence of blood antifreeze proteins – the polar ecosystems would be quite different. Many polar birds, seals and whales prey upon the polar fishes and they make up a large portion of their diet. If the fishes were absent then there would only be invertebrates as a source of prey and the diversity of the bird and seal fauna would be much reduced.’

Professor DeVries has devoted his career to studying how these proteins function to permit survival at extremely low temperatures. In this article, we take a look at his fascinating research career and some of his key results and motivations. His work has involved challenging research in remote Polar Regions to catch fish samples and determine how their evolutionary adaptations in antifreeze proteins make them uniquely suited for life in the freezer.

Professor DeVries’ discovery of antifreeze proteins in the late 1960s

Professor DeVries discovered antifreeze proteins while working as a young researcher in the 1960s. He was based on the shore of McMurdo Sound on Ross Island at McMurdo station, a major Antarctic research base run by the United States Antarctic program. Here, he tells Scientia how he came to be involved in this type of research and what he enjoyed about it: ‘I heard about a research position in Antarctica with a professor from Stanford University and applied and spent 13 months at McMurdo Station, Antarctica in 1961 performing an investigation of the respiratory metabolism of the endemic notothenioid fishes caught in the Sound. I enjoyed the combination of rigorous field work (catching the fish) and laboratory work in this remote location.’ He went on to explain how he made his fortuitous discovery of antifreeze proteins: ‘During these experiments I noticed that a deep water notothenioid fish would freeze to death if any ice was present in our refrigerated salt water while those caught in the shallow water survived in the presence of ice. I decided to investigate why there was a difference in these species living in water of the same temperature (-1.9°C) for my PhD thesis research at Stanford. I investigated what compounds were responsible for their capability to avoid freezing in this environment while fishes in temperate waters would freeze to death at -0.8°C. My study culminated in the discovery of the antifreeze glycoproteins, the compounds responsible for their extreme freeze avoidance.’

In his early characterisation of this extreme freeze avoidance, Professor DeVries showed that the freezing point of the serum of such fish was -2°C, which was well below the freezing point of the serum of fish that inhabit warmer waters. Additional salt content in the serum of the cold-water fish could only explain a portion of this difference and the balance was largely because of the presence of antifreeze glycoproteins.

This discovery of antifreeze proteins has opened up a completely new field of research into biological antifreezes, with labs all over the world now investigating these proteins, their occurrence in nature and use in biotechnological processes.

The latest development in this research has been the somewhat surprising discovery that antifreeze proteins also prevent ice crystals from melting. This more recent research was carried out in collaboration with Dr Paul Cziko of the University of Oregon and Professor Chi-Hing Cheng of the University of Illinois. The team found that ice that had been stabilised through binding with antifreeze proteins resisted melting and would not melt until exposed to much higher temperatures than expected. This was true both in the laboratory and also in living fish specimens. It is thought that the ice crystals present in polar fishes arise from their external environment and are introduced into their bodies through processes such as feeding or water entering their gills. It had been previously observed that the bodies of polar fishes contained ice crystals in locations such as their blood and spleen. It was unclear if the fish somehow eradicated these crystals or if they melted during summer warming periods. The team monitored water temperatures in Antarctica for about ten years and concluded that the water temperatures never got high enough to cause the ice crystals inside the fishes to melt, especially given that they were stabilised with antifreeze proteins. Some Arctic fishes, in contrast, encounter seasonal warming, and so do not require antifreeze proteins year-round. Fascinatingly, these fishes degrade their antifreeze proteins in the summer to conserve energy, to build up their reserves again in the autumn in preparation for the cold winter.

However, for fishes in the colder Antarctic climate, with a year-round complement of antifreeze proteins it is currently unclear if they are able to eradicate the protein-stabilised ice crystals from their bodies. If not, and they continue to accumulate for the entire lifetime of the fish, it is unknown if they result in adverse effects, such as blockage of blood vessels or production of inflammatory reactions. If so, then the unique adaptation that enabled such fishes to thrive in this hostile environment, antifreeze proteins, could also come with a down side, as they appear to contribute to accumulation of the crystals. This question of ice crystal accumulation and eradication is the current focus of Professor DeVries’ research. He believes that there must be a method that the fishes use to eradicate the crystals: ‘The fishes must have a biological mechanism for ridding themselves of these ice crystals because if they continue to accumulate them, one would assume that the ice burden would become so great that it would overwhelm their physiological systems. Thus, how do the fishes avoid accumulating detrimental levels of ice’. How indeed?