Bacteria can’t make snow… or can they? by Megan Smith-Cerdán

When you’re skiing in a ski resort with artificial snow, what crosses your mind as you gracefully glide (or fall) down those gigantic slopes? Perhaps you wondered where on Earth all this fake snow even came from? I bet you didn’t think bacteria made it possible.

Scientists have been battling with the creation of artificial snow for many years, the first attempted use being in 1946 where they dropped super-cooled ice crystals over the clouds of Mount Greylock in Massachusetts. Attempts at manipulating the weather developed greatly during World War II when scientists at the General Electric Research Laboratory wanted to create fog to mask ships out at sea. It was in 1932 that Irving Langmuir, a Nobel prize winning chemist, encouraged the likes of Vincent Schaefer to join the General Electric Research Laboratory as his research associate. The race to produce artificial snow had commenced and word got out in 1936 that scientists at the University of Japan had managed to create artificial ice crystals in the laboratory. This was the catalyst Schaefer needed, and in 1940 he successfully created replicas of snowflakes from thin plastic sheeting. Although the war interrupted his particular research focus, soon after Schaefer was experimenting with cloud formation in a closed chamber. When he added dry ice to drop the temperature of the chamber to allow cloud formation, water vapour surrounded the dry ice and to the scientist’s surprise, he had created rain and snow crystals. This is the backstory to Schaeffer’s breakthrough which lead to the experiment over Mount Greylock. It was Schaeffer’s method which was used to infiltrate clouds with dry ice in an attempt to create snow.

If only these scientists knew about the bacterium Pseudomonas syringae. This bacterium contains a protein on its surface which facilitates ice formation at higher temperatures (around -4oC to -2oC). The ice-nucleating protein (INP), found on their surfaces, works by forcing the water molecules it is in contact with into an alignment which promotes freezing and formation of ice crystals. This is a fairly recent discovery made in 1975 by Steve Lindow, a graduate who was studying plant pathology at the University of California at the time. Why would a plant pathologist discover this? It is because these bacteria infect many frost-sensitive plants. They use the proteins on their surface to form ice crystals which pierce into the plants, creating more holes for bacteria to enter through. Once inside, they take up plant nutrients and inject proteins to prevent bacterial recognition and alter functions in the cell- helping bacterial colonies to expand.

Retreating back to the subject of artificial snow slopes, in 1987 Snowmax® was the first commercialised artificial snow product. Snowmax® has been on the market for over 25 years, selling a powder which when mixed with water makes fake snow. One of the additives in the powder contains proteins (including INP from P. syringae) that allow water to freeze at higher temperatures. It is a very successful global company; however, it has suffered some criticism over the use of bacteria as an additive. Snowmax® (along with other artificial snow brands) has been banned in some places such as Austria and Bavaria, and since 2005 there has been a moratorium (temporary prohibition of activity) in place in France due to health and environmental concerns. Whilst Carmen de Jong, a hydrologist from the University of Strasbourg in France says that “different studies have shown that Snowmax can have a very negative impact on human health”, others disagree. Professor Richard Braun, who investigated the use of Snowmax® for the Swiss Biolink Institute, stated that it is “…produced from inactivated micro-organisms and is harmless to the health of humans, animals and plants”. However, as a result of global warming around half the Swiss ski resorts use artificial snow and therefore Professor Brown’s opinion may be considered to be biased.

Three predominant threats to human health were considered when the French Agency for Environmental and Occupational Health Safety (Afsset) were called in to assess the risks of bacterial additives in artificial snow- infection, toxicity and allergy. Another consideration was the promotion of growth of other microorganisms in the water due to P. syringae.

Infection- There is no pathogenic capacity of P. syringae to humans seeing as they can’t survive temperatures above 32oC, lower than our average human body temperature (37oC). Apart from the fact they have been used for about ten years for the biological control of post-harvesting blight in fruit, many of which we eat raw.

Toxicity- It is all in relation to the endotoxins found on the surfaces of a classification of bacteria known as Gram-negative (of which P. syringae falls under). Endotoxins trigger inflammatory and haemodynamic (blood flow) responses post-contact with mucous membranes (respiratory, ocular and gastrointestinal) and skin. These responses are what trigger asthma and pulmonary or respiratory dysfunctions. The results of acute toxicity studies on rats showed characteristics such as significantly increased lung weight, but it only caused slight irritation- no infection was found. Additionally, these endotoxins are found in many other bacteria which we as humans are frequently exposed to without any risk, hence it is determined that the products don’t pose any additional toxic danger.

Allergens- It has been noted that P. syringae has some antigenic structures which could trigger immune responses when in contact with mucous membranes, skin or even wounds. Antibodies associated with this immune response have been reported in humans. However, there is still room for more research into the specificity of the immune responses.

Other microbial life- It has been reported that the P. syringae derived products and nutrients in the artificial snow powder can promote the growth of other pathogenic microorganisms found naturally-occurring in the water used to mix the powder with. This means that although the additive bacteria may be harmless, the pathogenic microbial life it supports could be a health risk.

So, the Jury is still out… Will you be skiing this summer?

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