It sounds like a creature from a sci-fi thriller: a deep-sea supergiant organism that can survive more than five years without a single meal.

Yet for the supergiant isopod, a distant relative of the common pill bug found in gardens with the size of a chunky tablet, this extreme fasting ability is simply an everyday strategy for surviving in one of the most food-starved habitats on Earth.

Now, Chinese scientists have cracked the mystery of these supergiant isopods. The answer lies in a gene "hijacked" from bacteria and reprogrammed to work like a finely tuned energy-saving switch.

A joint research led by the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) based in Qingdao, east China's Shandong Province, in collaboration with the Hong Kong-based Chinese University of Hong Kong and Northwestern Polytechnical University in Xi'an, capital of Shaanxi Province, published their findings in the international journal Cell.

"Our work not only successfully 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," said Yuan Jianbo, a researcher at IOCAS and first author of the study paper.

The deep sea is cold, dark and almost entirely devoid of reliable nutrition, making long-term survival a remarkable evolutionary feat.

To survive the abyss, the isopod evolved a two-pronged "increase revenue and reduce expenditure" strategy. First, it possesses an enormous stomach that occupies about two-thirds of its body and acts like a deep-freeze pantry, allowing it to gorge when food is available and store the haul for months or even years.

Second, it maintains an exceptionally low basal metabolic rate, essentially putting itself on permanent energy-saving mode. Together, these traits turn opportunistic binge eating into an ultra-long energy reserve.

But the real surprise came when the team discovered that a key gene involved in this metabolic slowdown, named ND1, was not originally part of the isopod's own genome.

Instead, the isopod "hijacked" it from an external symbiotic bacterium through a process called "horizontal gene transfer."

"Think of it as biological copy-paste. An animal snatches useful DNA directly from a completely different organism," said Yuan.

This "stolen" gene then underwent epigenetic optimization, allowing the isopod to fine-tune its energy use with remarkable precision.

To verify ND1's function, the researchers inserted the gene into zebrafish, nematodes and human cells in the lab. Under normal temperatures, the gene recipients burned energy faster and became less tolerant of starvation.

However, under cold conditions that mimic the isopod's deep-sea home, ND1 flipped its role: it suppressed energy metabolism, reduced mitochondrial activity and boosted starvation endurance in zebrafish by a remarkable 37%.

This temperature-dependent switch solves the so-called "energy paradox" – how can a giant animal with high energy demands survive where food is extremely scarce?

The ND1 acts as a metabolic thermostat, fine-tuning energy burn in response to environmental conditions. It provides a neat solution to the trade-off between body size and food scarcity, according to Yuan.

The discovery of how the deep-sea isopod balances its giant body size with an ultra-low metabolic rate and of the key regulatory gene ND1 that enables this balance, may hold value for several applied fields, according to the researchers.

Possible future applications include longevity research, obesity treatment and aquaculture breeding, where understanding efficient energy management could inspire new approaches to health and food production, said Yuan.