Weird Science | Wriggling worms and the state between life and death

The answer is as mysterious as the question itself: the roundworms, also known as nematodes, were never really dead. They were in a state “between life and death” called cryptobiosis, in which their metabolism was shut off to levels so low that it could no longer be detected. Knowledge about cryptobiosis is still emerging.

Here's what we know so far

You know about hibernation, in which some animals go into a state of inactivity that’s deeper than sleep. In sleep, our heartbeats and respiration slow down, but metabolism remains unaffected. In hibernating animals, the heart and respiration rates fall to extremely low levels while metabolism also goes low. Digestion, for instance, stops completely; a hibernating animal does not urinate or defecate.

Cryptobiosis, like hibernation, happens in response to extremely harsh conditions, but involves even deeper inactivity.

While hibernation is a lowered metabolic state for several months, cryptobiosis is a state of undetectable metabolic rate that can last several millennia. Organisms that go into cryptobiosis include nematodes, tardigrades (more about them later) and even some plants.

Hibernating animals, such as bears, rodents and reptiles perform their minimal metabolic functions with energy they had stored during less harsh months. In cryptobiosis, organisms use a sugar called trehalose to protect their DNA, cells and proteins from degradation, Philipp Schiffer, an evolutionary biologist with the University of Cologne, said over email. “Hibernation is much more like deep sleep, whereas cryptobiosis is a state between life and death,” said

Schiffer oversaw the recent study (with a straightforward title: A novel nematode species from the Siberian permafrost shares adaptive mechanisms for cryptobiotic survival with C. elegans dauer larva') on the revived nematodes, published in PLOS Genetics.

The nematodes were discovered in 2018 in a sample from the Siberian permafrost, a permanent sheet of ice that is known to preserve organisms from several millennia ago. Anastasia Shatilovich, a soil scientist with the Russian Academy of Sciences, revived nematodes that year itself, and her team published the results in Doklady Biological Sciences.

That study, however, identified the nematodes as belonging to two known species, Panagrolaimus detritophagus and Plectus parvus. It also estimated the age of the permafrost deposits (in other words, the duration for which the worms were frozen) as being 30,000–40,000 years.

The new study in PLOS Genetics, which involves researchers from institutes in Germany and Russia, with Shatilovich among the authors, however, placed the worms under a new species named Panagrolaimus kolymaensis. Schiffer, who was not involved in the previous study, explained the misidentification: “This is, of course, because they are such tiny little creatures and very hard to identify by eye even under the microscope. They are mostly about 1mm in length.”

When the animals were defrosted in 2018, the scientists saw them wriggling. While the study that year dated the deposit at 30,000–40,000 years, subsequent media articles variously put it at 40,000, 41,000 or 42,000 years. Since then, a radiocarbon analysis of plant material from the site revealed that the frozen permafrost deposits had not thawed since the late Pleistocene, an age between 45,839 and 47,769 years ago.

In the latest study, scientists from institutes in Dresden, including the Max Planck Institute for Molecular Cell Biology and Genetics, created a complete genome sequence and analysis of one of the nematodes. Schiffer and colleagues then determined the species and found it was a new one. They compared its genome with that of a known nematode species, Caenorhabditis elegans, and found that certain genes, responsible for cryptobiosis, were common to both species.

So, what mechanism helped Panagrolaimus kolymaensis and Caenorhabditis elegans survive? Mild dehydration before freezing helped the worms prepare for cryptobiosis, and helped survival after freezing at –80°C. Both species produced trehalose when mildly dehydrated in the lab, which may have enabled them to survive.

Other such creatures

Cryptobiosis was first detected in 1702. Antonie van Leeuwenhoek, the pioneering Dutch microbiologist known as the father of microscopy, observed microscopic organisms in sediment collected from house roofs. He dried them, added water, and found that the animals began moving around again, according to the Carleton University, Ottawa, which adds that those organisms were likely nematodes or rotifers, a kind of free-swimming planktons.

The longest-known spell of cryptobiosis involves bacteria, at 25–40 million years. This was detected in 1995, when scientists revived and identified a species of bacterial spore from the abdominal contents of extinct bees. The bees had been preserved in buried Dominican amber. Among plants, a lotus seed found in an ancient Chinese lake, which was 1,000–1,500 years old, was subsequently able to germinate.

The best-known cryptobiotic creature, however, is the tardigrade, also known as the water bear. Found all over the world in water bodies and wet soil, these tiny organisms measure less than 1mm. It is only under the microscope that you can see that a tardigrade looks like a bear, only with four pairs of legs instead of two. The name “little water bear” was given by the German Johannes Goeze described one in 1773.

There are more than 1,000 different species of tardigrades, and have been on Earth for more than 500 million years ago, according to soil scientist Thea Whitman, writing on the University of Wisconsin website. Extremely resilient, they can survive temperatures as low as –130°C and high as 100°C, extreme pressure, and high radiation, Whitman writes.

They can also survive in a space vacuum. In 2007, European Space Agency scientists dried out some tardigrades and launched them in a rocket that remained in Low Earth Orbit for 10 days. Once back, they were rehydrated and “restored to life”.

In cryptobiosis, tardigrades lose their water and shrivel into a dehydrated form. They have been known to resume “life” after several years, and are a key species for scientists trying to understand how certain organisms preserve their DNA, which helps them during cryptobiosis. And there is still a lot to understand about cryptobiosis.

“It is by far not understood,” Schiffer said. “We (in the new study) just provide some additional results, more knowledge. Science is a stepwise process with many small findings adding up.”

Kabir Firaque is the puzzles editor of Hindustan Times. His column, Weird Science, tackles a range of subjects from the history of inventions and discoveries to science that sounds fictional, but it isn't.