Various firsts achieved in deep-sea expedition

陈小将

Chinese scientists have identified 7,564 species of prokaryotic microorganisms — 89.4 percent of them previously unreported — during an expedition to the hadal zone, the deepest part of the ocean floor.

The diversity of the microorganisms is comparable to the total number of already known marine microorganisms worldwide, researchers said.

The expedition, which was conducted using China's self-developed human-occupied vehicle Fendouzhe, also marked several milestones in deep-sea exploration. It included the first human descent to the deepest point of the Yap Trench in the western Pacific Ocean, a region nearly 9,000 meters deep where multiple ocean currents converge. The area is closely linked to the human living environment and climate change, scientists said.

Other firsts included a systematic study of hadal zone ecosystems and the creation of a database of hadal microorganisms. The database, now open for global sharing, contains an amount of data equivalent to that collected in global marine microbial research over the past decade.

"These achievements mark China's entry into the forefront of deep-sea life sciences research," the researchers said.

The hadal zone, defined as ocean regions deeper than 6,000 meters, remains one of Earth's least explored extreme environments.

"Our research showed hadal zone microbes exhibit extraordinary novelty and diversity, demonstrating immense resource potential in terms of new genes, structures and functions," said Xiao Xiang, a professor at Shanghai Jiao Tong University's School of Life Sciences and Biotechnology. Xiao is the initiator and lead scientist of the Mariana Trench Environment and Ecology Research project, or MEER.

"These resources may provide new options for addressing global depletion of biological resources and open up possibilities for innovative applications in biotechnology, medicine and energy," Xiao said.

The first phase of the MEER research was a joint effort of Shanghai Jiao Tong University, the Institute of Deep-sea Science and Engineering at the Chinese Academy of Sciences, and genome research organization BGI Group. Four related papers were published on March 7 as a cover feature in the journal Cell.

The expedition took place from October to December 2021. Scientists aboard Fendouzhe systematically explored depths between 6,000 and 11,000 meters in the Mariana Trench, Yap Trench and the Philippine Basin, collecting more than 2,000 samples of water, sediments and microorganisms. Twenty-one scientists participated in the voyage, with 17 descending for sampling and research.

Fendouzhe, China's first human-occupied vehicle capable of reaching 10,000 meters, is the only submersible in the world with the ability to conduct systematic sampling and research in the hadal zone, researchers said.

By analyzing 1,648 sediment samples, 622 samples of Hirondellea gigas — a deep-sea shrimp-like species — and 11 categories of deep-sea fish, the research team made several discoveries. These included strategies used by hadal microorganisms to survive in extreme high-pressure, low-temperature and low-nutrient environments.

"The extreme simplification of antioxidant pathways in these organisms may provide new insights for combating oxidation, aging and disease in humans," said Zhao Weishu, a researcher on the team.

The team also found that some hadal organisms consume refractory carbon compounds — generally difficult to be utilized — as a food source in their nutrient-scarce environment.

Xiao said the database compiled from the expedition serves as an irreplaceable record of hadal life between October and December 2021. The research team has made the database publicly available and called for international collaboration.