Posts tagged liquid gases

With the increased interest in Comet 67P and ESA’s robot lander, Philae, this seems an opportune time to take a look at a small set of experiments carried out by Prof Beijerinck at the end of the 19th century. During the 1870s, there had been suggestions that life could have come to Earth from comets, but the discussion was largely theoretical until physicists found ways to replicate the temperatures found in space by liquefying gases.

In April 1907, Professor Heike Kamerlingh Onnes of Leiden University gave a demonstration of his new equipment for producing liquid gases (especially hydrogen) at the 11th Congress of the Holland Society of Sciences in Leiden. Beijerinck had been a member since the foundation of the Society in 1888 and it’s hard to imagine that he missed a chance to tour Kamerlingh Onnes’ brand new laboratory. It’s surely not a coincidence that in November and December of that year, he and his assistant, C.J. Jacobsen, took microorganisms from their collection to Leiden in order to test their ability to survive such extreme cold.

The experiments were very simple. They used a collection of microorganisms that they knew well, and whose behaviour under normal conditions they could predict. They chose bacteria that could make acid from milk and others that make their own light (bioluminescent), as well as cyanobacteria (also called blue-green algae). Among the “higher” microorganisms were yeasts that can make survival forms called spores, and others that can’t, as well as a couple of fungi which also make spores, and a green alga. Small amounts of each organism (in their growth medium) were sealed in small vials and then frozen in liquid nitrogen (N2; freezes at -195.8°C) or liquid hydrogen (H2; freezes at -253°C) for different lengths of time. The growth and behaviour of the microorganisms were then compared with cells that had not been frozen.

The first experiments used liquid N2 (probably because it was easier to produce) for 15 minutes. The second series used liquid N2 for 10 hours or liquid H2 for 45 minutes. The third series involved liquid N2 for 3 and 11 days. Finally, the microorganisms that had survived best were compared in liquid N2 over periods up to 15 days.

There was little difference between the N2 and H2 results – once the organisms were deep frozen, the extra drop in temperature made no obvious difference. The length of time frozen also made little difference. Survival varied with the microorganism involved. The spores of the fungi and yeast that could make them survived, but their active cells didn’t. The bacteria survived. The cyanobacteria all died and the higher green alga survived.

From these simple experiments, it could be concluded that simple microorganisms such as bacteria and organisms that make survival spores could survive in comets. Beijerinck also commented that extreme cold could not be used as a means of sterilisation.

Deep-freezing microorganisms appears to have been a curiosity for Beijerinck and he does not seem to have returned to the subject. We now know that more complex cells can survive if they are suspended in a solution with suitable protection, and they also do better if they’re frozen and thawed correctly. 100 years after Beijerinck’s experiments, deep freezing (usually in liquid N2) is now used to safely store all sorts of biological material from research stocks of bacteria and viruses to human sperm and tissues.