International Freezer Challenge: Who Saves the Most?

Tip: Pay attention to the storage temperature

Many samples and kits are stored at -80 °C despite the fact that this is often not even necessary. Most proteins, bacteria, yeast and fungi can be stored for years at -70 °C [6, 7]. Manufacturers actually recommend a storage temperature of -70 °C for some kits [8]. Depending on the freezer, simply reducing the temperature to -70 °C can reduce energy consumption by up to 40%. Many universities have already taken steps to reduce the set point of their freezers. 50% of the freezers at the University of Colorado Boulder are set to -70 °C, and the Center for Disease Control and Prevention reduced energy consumption by 40% after introducing the change [9]. Also, many samples such as molecular biology substances and proteins do not necessarily need to be stored at -70 °C. A storage temperature of -20 °C is sufficient. This is especially the case when the samples are only stored for a short time. Stability studies on DNA and RNA have shown that it makes no difference whether the samples are stored at -20 °C or -80 °C for short duration. RNA remains just as stable for one month whether it was stored at -20 °C or -80 °C [10]. The same is true for genomic DNA. Stability remained the same for 24 months at both temperatures [11]. Normally, DNA and RNA samples are stored at low temperatures. But methods have existed for several years which allow storage of DNA and RNA at room temperature [12, 13]. To do that, DNA is immobilized on specially impregnated cellulose cards, in a special matrix [15] or in special glass-metal tubes in the absence of oxygen and moisture [16]. Storage of DNA on FTA cards is fast and simple. The FTA cards are made of specially impregnated cellulose. Drops of the sample under investigation, for example blood, plant material or bacterial cells, are applied to a card and then dried. The cells are lysed on the surface, and the DNA that is released is immobilized in the cellulose matrix. The coating denatures any nucleases which may be present, and growth of microorganisms is also inhibited during storage. The manufacturer GE Healthcare claims that samples can be stored for up to 17 years with no degradation. A small section is punched out for DNA analysis, and the DNA is then eluted according to a prescribed protocol. The isolated DNA can be used in further downstream applications [14]. Another method is based on an anhydrobiosis mechanism borrowed from nature. It is found in tardigrades (water bears) and brine shrimp. These animals can survive phases of extreme aridity and near total dehydration. Rehydration restores the original life functions. Storage technology is based on the formation of a thermostable, protective vitrified layer around the DNA or RNA during drying, preventing degradation at room temperature [15]. The sample is absorbed into a special matrix. Gentegra uses a special chemical matrix which embeds the DNA in a sort of “cocoon” [17]. Kits made by Biomatrica create a protective seal around the DNA, a process which the company calls “shrink wrapping” [18]. With this method, it is important that the samples are completely dehydrated and do not come into contact with water during storage. To analyze the samples, water is simply added. The DNA or RNA is recovered from the matrix, and it can then be used for further analysis without any purification step. A final method for storing DNA and RNA is marketed by the French company Imagene. The samples are sent in, dried and then sealed in the complete absence of water and oxygen in special glass vials encased in metal shells. This guarantees that stored DNA and RNA are not exposed to hydrolysis processes caused by air humidity or attacks by oxygen radicals [16]. Besides saving energy, other advantages include much more compact storage, lower costs and enhanced safety. During a power outage, valuable samples stored in a freezer can be irretrievably lost. That is not the case when the samples are stored at room temperature. Molecular biology reagents and kits are also available that can be stored at room temperature. Ready-To-Go beads (RTG beads) have been on the market for years. They contain the lyophilised reagents needed for a PCR reaction (except for the template and primer) in a special matrix. The beads are supplied in a PCR tube, and the user adds the correct amount of water, template and primer, and starts the reaction as usual [19]. All of this may eliminate the need for a refrigerator or freezer. If so, the time has come to dispose of the oldest “energy guzzler”. Maybe sufficient funds are available to buy a new one? Energy efficiency should be one of the purchase criteria. Lower energy costs may well offset the higher price tag over the useful life of the refrigerator or freezer. Attention should be paid to the information provided by the manufacturer. The Energy Star label specifies energy efficient laboratory freezers and refrigerators, but it only exists in the US. Furthermore, the Egnaton-Cert certification standard, which is currently under development, will assess the sustainability performance of a wide range of lab equipment, including freezers. Another way to save energy is to share freezer storage space with a colleague or another group in your institute. Large freezers are relatively more energy-efficient than smaller ones.

So what else is there for sample management?

Many labs also do other things to save energy. One idea is to sort samples into long-term and short-term samples and store them separately. In protein purification, maybe not all of the chromatography steps have to be performed in a cold room. Many proteins are stable at room temperature and can be purified at this temperature. Not all are suitable for every lab, but by taking a critical look at sample management, opportunities for improvement will undoubtedly be found. With the Freezer Challenge, labs have until May 1, 2018 to take action, share information on examples of best practice, reduce resource consumption and possibly even win a prize.

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