Scientists Discover Thousands of New Microbial Species Thriving in the Mariana Trench

A human can’t survive in the Mariana Trench without protection. At its deepest, the trench plunges 35,000 feet below the surface of the Pacific Ocean to a region reigned by crushing pressure and darkness.

Yet somehow life finds a way. The hadal snailfish, with delicate fins and translucent body, roams the dark and freezing waters. Giant shrimp-like creatures up to a foot long scavenge fallen debris, including wood and plastic, and transparent eels with fish-like heads hunt prey. A carpet of bacteria breaks down dead sea creatures and plankton to recycle nutrients.

We’ve only scratched the surface of what thrives in the deepest regions of the ocean. But a large project has now added over 6,000 new microbes to the deep-sea species tally.

Called the Mariana Trench Environment and Ecology Research Project, or MEER for short, a team of scientists have collected sediment from the hadal zone—the deepest part of the ocean—in the Mariana Trench and two other areas. The investigation revealed thousands of new species and two adaptations allowing the microbes to thrive under intense pressure.

Another team assembled the genomes of 11 deep-sea fish and found a mutated gene that could boost their ability to survive. Sequencing the genome of a giant shrimp-like creature suggested bacteria boosted its metabolism to adapt to high-pressure environments.

Studying these mysterious species could yield new medications to fight infections, inflammation, or even cancer. They show how creatures adapt to extreme environments, which could be useful for engineering pressure- or radiation-resistant proteins for space exploration.

“The deep sea, especially hadal zones, represents some of the most extreme and least explored environments on Earth,” wrote study author Shunping He and colleagues at the Chinese Academy of Sciences. The project hopes to “push the boundaries of our understanding of life” in this alien world, added Shanshan Liu and her team at BGI research, in a separate study.

Meet MEER

Oceans cover roughly 70 percent of the Earth’s surface. Yet we know very little about their inhabitants, especially on the ocean floor.

Since the 1960s, multiple missions—some autonomous, others manned—have sought to explore the deepest part of the Pacific Ocean, the Mariana Trench. Over 30,000 feet deep, it could completely submerge Mount Everest.

The trench is an unforgiving environment. The pressure is over 1,000 times greater than that at sea level, and at Challenger Deep—the deepest point navigated to date—the temperature is just above freezing. The seabed there is shrouded in complete darkness.

Yet a manned descent 65 years ago found flatfish and large shrimp-like creatures thriving in the trench—the first signs that life could survive in such extreme environments. More recently, James Cameron, best known for directing films like Titanic, dived to nearly 36,000 feet and took footage that helped identify even more new species.

The deep sea, it seems, is a trove of alien species yet to be discovered. The MEER project is collecting specimens from the deepest trenches across the world to learn more.

MEER relies on a deep-sea submersible called Fendouzhe, which means striver or fighter in Chinese. Fendouzhe is self-propelled and can survive freezing temperatures and tremendous pressure. It holds three crew members and has two mechanical arms bristling with devices—cameras, sonars, drills.

The submersible reached the bottom of the Mariana Trench in 2020 followed by missions  to the Yap Trench and Philippine Basin. Scientists on board gathered over 1,600 sediment samples from multiple hadal zones between 6 and 11 kilometers, or roughly 4 to 7 miles, under the sea.

Added to the punishing pressure and lack of light, the deep sea is low on environmental nutrients. It’s truly “a unique combination that sets it apart from all other marine and terrestrial environments,” wrote the authors.

Undersea Genes

Sediments hold genetic material that survives intact when brought to the surface for analysis.

One study sketched a landscape of living creatures in the deep ocean using an approach called metagenomics. Here, scientists sequenced genetic material from all microbes within an environment, allowing them to reconstruct a birds-eye view of the ecology.

In this case, the collection is “10-fold larger than all previously reported,” wrote the team. Over 89 percent of the genomes are entirely new, suggesting most belong to previously unknown microbial species living in the deep ocean.

Samples collected from other trenches have varying genetic profiles, suggesting the microbes learned to adapt to various deep ocean environments. But they share similar genetic changes. Several genes bump up their ability to digest toluene as food. The chemical is mostly known for manufacturing paints, plastics, medications, and cosmetics.

Other genes wipe out metabolic waste products called reactive oxygen species. In large amounts, these damage DNA and lead to aging and disease. The creatures also have a beefed-up DNA repair system. This could help them adapt to intense pressure and frigid temperatures, both of which increase the chances of these damaging chemicals wreaking havoc.

Deep-Sea Superpowers

Meanwhile, other studies peered into the genetic makeup of fish and shrimp-like creatures in the hadal zone.

In one, scientists collected samples using the Fendouzhe submersible and an autonomous rover, covering locations from the Mariana Trench to the Indian Ocean. The team zeroed in on roughly 230 genes in deep-sea fish that boost survival under pressure.

Most of these help repair DNA damage. Others increase muscle function. Surprisingly, all 11 species of deep-sea fish studied shared a single genetic mutation. Engineering the same mutation in lab-grown cells helped them more efficiently turn DNA instructions into RNA—the first step cells take when making the proteins that coordinate our bodily functions.

This is “likely to be advantageous in the deep-sea environment,” wrote the team.

Top predators in the deep rely on a steady supply of prey—mainly, a shrimp-like species called amphipods. Whole genome sequencing of these creatures showed the shrimp thrive thanks to various good bacteria that help them defend against other bacterial species.

There are also some other intriguing findings. For example, while most deep-sea fish have lost genes associated with vision, one species showed gene activity related to color vision. These genes are similar to ours and could potentially let them see color even in total darkness.

Scientists are still digging through the MEER database. The coalition hopes to bolster our understanding of the most resilient lifeforms on Earth—and potentially inspire journeys into other extreme environments, like outer space.