On 25 Aug 2026, researchers from the Deep-Ocean Microbial Ecology and Technology (DOTME) team of the School of Oceanography, Shanghai Jiao Tong University (SJTU-SOO), together with collaborators from the Institute of Geology and Geophysics, Chinese Academy of Sciences, published a research article entitled “Redox-stratified macromolecule degradation supports microbial survival in the oligotrophic Kermadec Trench sediments” in Nature Communications. The study was conducted by Assistant Research Professor Yongxin Lv (first author), Peng Liu, Yan Liu, Associate Research Professor Liang Dong, Research Professor Jinhua Li, and Research Professor Yu Zhang (corresponding author).
Hadal trenches represent some of the most extreme habitats on Earth. The Kermadec Trench reaches a maximum depth of approximately 10,047 m and is characterized by permanent darkness and extremely high hydrostatic pressure. Its surface sediments are also markedly oligotrophic and low in oxygen. Primary productivity in the overlying South Pacific is relatively low, while labile organic matter is preferentially consumed during its passage through the water column. Consequently, readily degradable organic matter becomes increasingly limited, leaving microorganisms to rely more heavily on complex macromolecules.
Despite these harsh conditions, the bottom of the Kermadec Trench supports relatively high microbial abundance and activity. This raises an important question: how do microorganisms obtain carbon and sustain energy metabolism in sediments where organic-carbon input and oxidative capacity are both limited?
To address this question, the research team conducted deep-sea sampling with the aid of the Fendouzhe manned submersible and a sediment in-situ RNA fixation sampler developed by the team. By integrating metagenomic and metatranscriptomic analyses, the researchers investigated how hadal microorganisms acquire carbon substrates and regulate energy metabolism under extreme oligotrophic conditions.
The results show that the utilization of complex macromolecules represents an important strategy for carbon acquisition in the Kermadec Trench. Microorganisms were capable of degrading materials such as peptidoglycan and complex polysaccharides, thereby further recycling organic carbon contained in cellular debris and sinking particles. This recycling of relatively refractory organic matter provides substrates that can support microbial growth and energy metabolism in the carbon-limited hadal environment.
Additionally, oxygen is not the only terminal electron acceptor available to these microorganisms. The microbial communities can flexibly utilize oxygen, nitrate, nitrite, and other electron acceptors while degrading complex organic matter. The coupling between macromolecule degradation and diverse respiratory pathways therefore broadens the range of energy-acquisition strategies available under low-oxygen and oligotrophic conditions.
The study further revealed pronounced spatial differences in microbial respiratory strategies from the trench slope to the trench bottom. Microbial communities on the slope exhibited a greater tendency toward oxidative metabolism, whereas those at the trench bottom showed stronger signatures of reductive metabolism (Figure 1). These patterns suggest that redox stratification contributes to microbial niche differentiation across the trench. High hydrostatic pressure may also influence microbial respiratory activity and the use of terminal electron acceptors.
Together, these findings indicate that the survival of microorganisms in the deepest parts of the Kermadec Trench is supported by the coordination of two major strategies: efficient utilization and recycling of limited organic matter, and flexible adjustment of respiratory pathways according to local redox conditions.
Figure 1. Correlations between the transcriptional activities associated with electron acceptors and carbohydrate-active enzymes (CAZymes) in macromolecule-degrading metagenome-assembled genomes (MAGs) from trench-bottom and slope sediments.
An important methodological basis for these findings was the preservation of microbial RNA as close as possible to its in situ transcriptional state. With support from the Fendouzhe manned submersible, the research team used its independently developed sediment in situ RNA fixation sampler to fix RNA directly on the deep-sea floor (Figure 2). This approach minimizes alterations in microbial transcriptional activity that may otherwise occur as samples experience major environmental changes during recovery from hadal depths to the sea surface.
Since its first application in 2021, the sampler has been deployed during multiple expeditions in the Mariana and Kermadec trenches, as well as in the Chukchi and Bering seas. It has supported a series of subsequent studies, including research published in Nature Communications in 2024 and Microbiome in 2025. The technology provides an important tool for moving deep-sea microbial research beyond determining “what is present” to resolving “what microorganisms are actually doing” under in situ environmental conditions.
Figure 2. The Fendouzhe manned submersible, the sediment in situ RNA fixation sampler, and the sampler operating in the deep-sea environment.
This research was supported by the National Key Research and Development Program of China (2023YFC2812800), the Shanghai Pilot Program for Basic Research (21TQ1400201), the National Natural Science Foundation of China (42306104, 42188102, 42122043, and 42472370), and the State Key Laboratory of Submarine Geoscience (SGLabZZKT2025-01 and SGLabZZKT2025-09).
Link to the article:
Lv, Y., Liu, P., Liu, Y., Dong, L., Li, J., and Zhang, Y. (2026). Redox-stratified macromolecule degradation supports microbial survival in the oligotrophic Kermadec Trench sediments. Nature Communications.
https://doi.org/10.1038/s41467-026-77249-x
