This Giant Deep-sea Creature Survives Five Years Without Food, Thanks to a Borrowed Bacterial Gene

Living nearly 900 meters underwater, this isopod evolved unusual adaptations to thrive in the world’s most food-scarce environment.

In the dark depths of the ocean, food can be so scarce that animals may go months or even years between meals. Yet one creature has pushed the limits of frugality to an extreme. The deep-sea supergiant isopod, a distant relative of pill bugs that can grow to more than a foot long, has been documented surviving for over five years without eating. 

Scientists have long known about this remarkable endurance, but they have struggled to explain how such a large animal can afford the enormous energy costs of maintaining its body in one of Earth’s most nutrient-poor ecosystems. 

Now, in a new study, a team of Chinese researchers has uncovered how the giant isopod appears to solve a problem that should, in theory, be impossible. The answer involves both a highly specialized digestive system and a gene borrowed from microbes long ago.

“These findings uncover an exceptional evolutionary strategy whereby deep-sea megafauna co-opt and epigenetically optimize exogenous microbial genes to reconcile the metabolic conflict between energy-demanding gigantism and extreme energy limitation,” the study authors note.

A feast-or-famine body built for the abyss

Gigantism usually comes with high energy demands. However, deep-sea ecosystems are defined by chronic food shortages. Previous observations showed that giant isopods could gorge themselves when food appeared and then endure years without eating, but this was a very vague and unsupported explanation.

The new research suggests the animals solved the problem through a two-part strategy that allows them to store large amounts of food when opportunities arise and dramatically reduce the rate at which they burn energy afterward.

To understand how giant isopods survive such long periods without food, the researchers compared two closely related species that inhabit different depths. One was Bathynomus jamesi, a supergiant isopod found at depths of about 898 meters, while the other was Bathynomus doederleini, a smaller species that lives roughly 300 meters below the surface. 

They examined the animals’ body structures, measured physiological traits, analyzed their genomes, and investigated the microbes living inside their digestive systems to identify traits that might explain their unusual resilience.

The first clue came from the isopod’s digestive system. The team found that the deep-sea species (B. jamesi) has an unusually enlarged stomach that can retain food for extended periods. For instance, in the largest individuals, the stomach occupied nearly two-thirds of the body cavity, far larger than in their shallow-water relatives. 

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In an environment where a large carcass may be the only substantial meal an animal encounters for months, or even years, this adaptation allows the isopod to consume huge amounts of food in a single sitting and process it slowly over time. 

One captive individual reportedly ate 2.6 kilograms of food at once. The researchers say this episodic hyperphagia, essentially a feast-or-famine eating strategy, helps the animal capitalize on rare feeding opportunities. 

They also found that their stomachs host a distinct microbial community enriched in bacteria linked to lipid metabolism, suggesting that the microbiome may play a role in how the animals manage energy reserves between meals. The researchers found that this oversized stomach works alongside an exceptionally low basal metabolic rate, allowing stored nutrients to be released and used slowly over long periods.

“Deep-sea isopods have a clever ‘earn more, spend less’ survival strategy,” Jianbo Yuan, lead researcher and a professor at the Institute of Oceanology, Chinese Academy of Sciences, told Reuters.

The bacterial gene that taught an animal to slow down

The researchers also sequenced the isopod’s genome. There, they identified a gene called ND1, which appears to have entered the isopod’s evolutionary lineage through horizontal gene transfer—a process in which DNA moves between unrelated organisms rather than being inherited from parent to offspring. Such transfers are common among microbes but are relatively uncommon in animals. 

“This is surprising because bacteria and animals are very different, and such transfers are extremely rare. The gene gives the isopod an extra tool to fine-tune its energy use, especially when it needs to slow down,” Yuan added.

The team found evidence that an ancient microbial version of ND1 was incorporated into the ancestors of B. jamesi. Over time, the gene was duplicated multiple times and evolved unusually high levels of expression, boosting its influence. 

The researchers also discovered that its activity is controlled through histone acetylation, an epigenetic mechanism that helps switch genes on or off without altering the DNA sequence itself.

To test whether ND1 plays a role in energy conservation, the scientists inserted the gene into zebrafish, nematodes, and cultured cells. The experiments revealed that ND1 behaves differently depending on environmental conditions. 

At normal temperatures, the gene boosts metabolic activity, but under cold conditions, similar to those found in the deep sea, it suppresses the activity of genes involved in energy production and reduces mitochondrial function, helping organisms conserve energy during starvation.

When metabolism was further suppressed by cold conditions, organisms expressing the gene survived longer without food than those that lacked it. In zebrafish, for example, ND1 extended starvation survival by about 37 percent under cold conditions. 

According to the researchers, this suggests the gene helps lower the body’s baseline energy requirements when food is scarce, allowing stored energy reserves to last significantly longer.

A new blueprint for surviving the impossible

Together, the findings reveal a dual survival strategy. The giant isopod first maximizes energy intake through an oversized food-storage organ and then minimizes energy expenditure through a metabolism-modulating genetic program. 

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This combination may explain how the species bridges the enormous gaps between feeding opportunities in the deep ocean. It also offers one of the clearest examples yet of how large animals can survive in environments where energy is perpetually scarce. 

“Our work not only deciphers the mystery of ultra-long starvation tolerance in deep-sea isopods but also provides an important paradigm for understanding how life balances growth and survival in extreme environments,” Yuan said.

Moreover, the study suggests that horizontal gene transfer may have played a bigger role in animal adaptation than previously thought. For example, in the giant isopod’s case, the study suggests that borrowed DNA may sometimes provide evolutionary shortcuts for adapting to extreme environments. 

However, at the same time, many questions remain unanswered. The experiments show that ND1 can alter metabolic activity in laboratory organisms, but researchers still need to determine exactly how the gene interacts with the isopod’s native biological systems and whether similar mechanisms exist in other deep-sea species. 

Hopefully, future work will provide answers to these questions and reveal whether borrowing microbial genes is a common evolutionary strategy among animals.

The study is published in the journal Cell.