Nature’s anti-freeze

Challenge:  Anti-freeze and de-icing solutions for ice cream, aircraft and organ transport

Natural solution:  Atlantic cod (Gadus morhua), snow fleas (Hypogastrura nivicola), winter rye (Secale cereale)

 

As winter quickly approaches, temperatures rapidly drop and icy mornings become more frequent.  Scraping frost from car windows and spreading salt on paths are a few ways people cope with icy conditions.  Some plants and animals, however, are able to live at temperatures that would normally freeze human blood.  The ability of these amazing organisms to survive at sub-zero temperatures is inspiring new technologies that will prolong the permissible travel time of organs for transplant, enhance the freezeability of ice cream and prevent ice build up on airplanes and electricity pylons.

Scraping ice from car windows and clearing snow - a few ways people cope with icy conditions © Amanda Gregory

 

As the temperature drops below freezing small ice crystals form inside plants and animals.  These ice crystals grow by drawing more water out of the surrounding cells, in the process the physical structure of the cells is destroyed so killing them.  However, many organisms have been found to contain unique molecules that scientists call antifreeze proteins (AFPs). These AFPs are capable of lowering the freezing point of a solution and so keep ice crystals very small or prevent their formation altogether.

 

The ability to prevent freezing has evolved independently in a wide range of cold-tolerant organisms1, for example, in bacteria, insects, plants, such as winter wheat and rye grass, and fish, such as Ocean pout and Atlantic cod.  Despite the number of different ways employed for surviving in freezing conditions, almost all organisms use antifreeze proteins (AFPs). 

 

Different types of AFPs, or isoforms, have been found in different types of species.  For example, polar fish AFPs are divided into five major groups which display differing properties: AFP Types I-IV and the antifreeze glycoproteins (AFGP)2.  These AFPs and AFGPs are able to substantially lower the freezing point of fish blood to below the freezing point of the surrounding seawater3

 

While polar fish live at temperatures of -1o to -2oC for most of their life, they are not subjected to the great temperature ranges of many terrestrial plants and animals.  Some terrestrial species also can survive temperatures well below freezing.  Accordingly, additional AFPs or isoforms have been discovered in insects.  These insect AFPs can be up to 20 times more effective and display higher thermal hysteresis, that is, the difference between the melting and freezing point2, than fish AFPs. 

 

Weaker AFPs have also been found in plants, such as winter rye (Secale cereal) and winter wheat (Triticum aestivum).  Six AFPs have been isolated from the apoplast (space between cells for free water movement) in the leaves of winter rye4.  Located in areas subject to icing; these AFPs function as a barrier to the formation or recyrstallisation of ice4.  Recrystallisation occurs when the temperature of a frozen body increases but still remains below the material's melting point.  Under these conditions, large ice crystals grow at the expense of small ones.  AFPs found in rye, wheat and barley, may have evolved from disease-related proteins and may now play a dual role both preventing freezing and enhancing disease resistance in overwintering plants4, 5.

 

The economic case

While the first AFPs were discovered in the 1960’s, the investigation of AFPs is still very much a developing area of science.  Increasingly though, it is recognised that these complex molecules could offer many technological advances often with significant economic potential.

 

Ocean Pout who’s antifreeze proteins can be found in some ice-cream and ice lollies © Kim Langille

Amazingly, the same antifreeze proteins that keep organisms from freezing in cold environments can also prevent ice from melting at warmer temperatures.  Unilever now use AFPs in some of their ice cream and ice lolly products.  While sourcing AFPs from fish stock would be environmentally and economically prohibitive, scientists have been able to develop genetically modified baker’s yeast (Saccharomyces cerevisiae) that contains the gene from the Ocean Pout (Macrozoarces americanus) associated with AFP formation thus producing Ice Structuring Proteins (ISPs) which act in the same way as AFPs.  The result is ice cream with improved consistency which maintains its shape for longer and does not melt as temperatures increase6

 

 

In 2009 the European Food Safety Authority endorsed the use of these modified ISPs. Unilever plans to sell Europe’s first ISP-containing ice creams in 2010.  All products containing ISP will include ISP in the ingredient list and information will be made available via customer care-lines and websites.  Low fat products and novelty ‘popsicle’ products have been on sale, and enjoyed, in the USA, Mexico, China, Philippines and Australia for several years6.  Between 2003 to 2007 more than 470 million ISP-containing edible ice products have been sold in the USA and 47 thousand litres of ISP containing ice cream has been sold in Australia/New Zealand7.  In 2009 the UK ice cream market was valued at £799 million.  It is expected to reach £819 million by 20148.  The ability to reduce and prevent the growth of large ice crystals in ice cream presents advantages and opportunities for the industry. 
De-icing plane prior to take off © University Corporation for Atmospheric Research

 

 

The challenge of keeping aircraft frost-free in winter is a major issue for many airlines.  Airlines take several steps in order to reduce de-icing related delays.  The development of ice-resistant paints and coatings, currently being undertaken by the Fraunhofer Institute for Manufacturing Technology and Applied Materials Research in Germany, could provide substantial cost savings9 as well as improved fuel efficiency.  The coatings being developed use paint with bonded AFPs which may protect the aircraft as well as prevent ice buildup – not only on the runway but during the flight.  In 2009 there was an estimated 74 billion aircraft flights worldwide10.  By 2013 the global air freight market is forecast to have a value of $119.5 billion11.  At an estimated cost of £50 per minute, delays can be a major burden to an airline’s bottom line12

 

Electricity and telephone cable and pylons bought down by snow and ice © University Corporation for Atmospheric Research

Utilities are also affected by ice, not only by the weight of ice on power lines bringing them down, but also where the ice acts as an insulator.  Here the ice causes the wires themselves to heat up, which means energy transmission along the wire becomes less efficient.  Effectively energy is lost that would otherwise be transmitted to consumer’s homes and businesses.  In 2008 over 500,000 people in the United States and 4.7 million people in Canada lost power as rain frozen on exposed surfaces brought down electricity pylons across much of the north-eastern United States and Canada13.  According to the National Climatic Data Centre (NCDC), the total economic loss due to this event was estimated at approximately US$4.4 billion, with US$3 billion in Canada alone13

Physical clearing of power lines by mechanical rolling © Manitoba Hydro

 
 

 

 

Treatments, such as AFP coatings, used to protect electric power lines and pylons could save utility companies millions of dollars in maintenance and repairs costs alone.  Additionally such coatings would also improve energy efficiency.

 
 

 

Probably one of the most exciting technologies under development is within the health sector.  AFPs could be used to preserve organs and tissues prepared for transplant.  With more than 7,500 people waiting on the UK organ transplant list14 the possibility of transporting organs to recipients further away or even storing organs for longer periods of time would have the most positive impact on human life. 

 

Researchers have now been able to produce synthetic AFPs derived from that of the snow flea (Hypogastrura nivicola), sfAFP, which demonstrate the same activity as the natural compound.15.  An added benefit of this sfAFP is that it loses its structure at higher temperatures.  This means that any synthetic sfAFP used in chilling organs for transplants will be broken down naturally when restored to body temperature and quickly cleared from the patient’s system thus reducing the possibility of an adverse reaction.16.

 

Biodiversity

Once again we see that biodiversity with which many of us may have little contact and may never see could be very important for many aspects of our lives.  Already, however, some of these important species, which are the source of AFPs, are threatened, for example the Atlantic Cod (Gadus morhua).

 

Atlantic Cod. (Gadus morhua) a polar species that produces and stores antifreeze glycopeptied proteins (AFGPs) in their blood © Dieter Craasmann

 

Atlantic cod have declined by 97% since the early 1970’s and recovery appears negligible17.  Some Canadian cod populations continue to decline even in the absence of commercial fishing.  Threats include over-fishing (now halted in many areas), predation by other fish and seals, and natural and fishing-induced changes to the ecosystem18.  Atlantic cod are listed as vulnerable on the IUCN Red list of endangered species.  The collapse of the North Atlantic cod fishery has put some 30,000 Canadians out of work and affected the economies of over 700 communities19.

 

Climate change, which has already been observed to be having significant impacts on global marine and terrestrial ecosystems, will continue to influence biological diversity.  Many species are susceptible to climate change, and those of the marine environment are particularly vulnerable.  The polar regions are undergoing more rapid environmental changes than elsewhere, in many instances due to the combined effects of natural climate change20, and human activity such as fishing, industry and changes to the natural environment.  Over the past 50 years the Western Antarctic Peninsula has warmed more than four times faster than the average rate of Earth’s overall warming21.  

 

The changes in temperature and sea ice are altering the marine and terrestrial habitats along with the types of species found and their abundance.  For example, scientists observe new species colonising the Antarctic while some native flowering plants are expanding their range due to warmer temperatures and populations of other traditional inhabitants, such as Antarctic krill (Euphausia superba) and silverfish (Pleuragramma antarcticum), are decreasing with associated impacts up the food chain.

 

Uncertainties exist as to how the complex physical and biological systems in Antarctica, and Arctic, will adapt as the Earth continues to warm21.  Increases in temperature and reductions in winter sea ice will undoubtedly affect the reproduction, growth and development of many marine and associated terrestrial species, leading to changes in distributions, further reductions in population sizes and in some cases even extinctions22.  Accordingly, it is still unclear how climate change will affect many of the species that benefit from AFPs, and thus how environmental change may put at risk our development of this potentially important new area of technology.

 

The unique features of AFPs have the potential for wide ranging application in the development of nano technology.  The move to synthetically or chemically produced AFPs depends on understanding about the organisms that live and thrive in the remote, and to us marginally habitable, areas of the earth.  Again this developing area of technology shows how we can exploit biodiversity without depleting the natural resource itself.

 

Images

Atlantic Cod - Pew Environment Group

Power lines bought down by ice/snow - University Corporation for Atmospheric Research

De-icing aircraft – University Corporation for Atmospheric Research

Cable clearing image – Manitoba Hydro

Ocean PoutKim Langille

 

References

  1. Doxey,  A.C. and McConkey, B.J. (2006)  AFPredictor: A computational screening protocol for antifreeze/ice-structuring proteins Nature Protocols  pp213.  Accessed November 2010
  2. Grunwald, I, Rischka, K, Kast, SM, Scheibel, T and Bargel, H  (2009)  Mimicking biopolymers on a molecular scale: nano(bio)technology based on engineered proteins.  Phil. Trans. R. Soc.  Vol 367: 1727-1747.  Accessed November 2010
  3. Peterson, I (1986)  A biological antifreeze: antifreeze proteins found in the blood of polar fish alter the way ice crystals grow.  Science News  Accessed November 2010
  4. Griffith, M, Antikainen, M, Hon, W-C, Pihakaski-Maunsbach, K, Yu, X-M, Chun JU ,& Yang DSC  (1997)  Antifreeze proteins in winter rye.  Physiologia Plantarum Vol:100, Issue 2, pp 327 – 332  
  5. Antikainen, M and Griffith, M (1997). Antifreeze protein accumulation in freezing-tolerant cereals  Physiologia Plantarum  Vol: 99, Issue 3,  pp423 – 432
  6. Unilever  Cool ice cream innovations  Accessed December 2010-12-13
  7. European Food Safety Authority (2008)  Safety of ‘Ice Structuring Protein (ISP) - Scientific Opinion of the Panel on Dietetic Products, Nutrition and Allergies and of the Panel on Genetically Modified Organisms  EFSA
  8. Watson, E (2010)  Mintel: UK ice cream sales up 7.5% to £799m in 2009.  Food Manufacture  Accessed November 2010
  9. Robson, D  (2007)  Fish 'antifreeze' inspires ice-proof paint  New Scientist  Accessed November 2010
  10. WorldAirportTraffic Report for 2009,  Airports Council International  Accessed November 2010
  11. Air Freight: Global Industry Guide (2010)  Accessed November 2010
  12. Met Office (2009)  BMI proves value of aircraft de-icing forecast service.  SITA  Accessed November 2010
  13. RMS Special Report  (2008)  The 1998 Ice storm: 10-year retrospective  Accessed November 2010
  14. National Health Service Blood and Transplant statistics.  Accessed November 2010
  15. Physorg  (2008) 'Snow flea antifreeze protein' could help improve organ preservation  Accessed November 2010
  16. Anon  (2005)  Natural antifreeze protein may help store human organs  The Medical News  Accessed November 2010
  17. Brooks, C  (2008)  No Recovery for Atlantic Cod Population Science Now Accessed November 2010
  18. Schedule 3  Species at Risk Public Registry.  Canadian Government  Accessed November 2010-12-13
  19. IUCN  (2009)  Ecosystem Management  Accessed December 2010
  20. Scientific Committee on Antarctic Research  (2009) Antarctic Climate Change and the Environment  Accessed December 2010
  21. Antarctic Treaty Consultative Meeting  (2008) Impacts of Climate Change on Antarctic Ecosystems  Accessed December 2010
  22. Scientific Committee on Antarctic Research  (2009) Antarctic Climate Change and the Environment:  10 Points  Accessed December 2010