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Thursday, October 08, 2026

HKUST researchers reveal a tiered adaptation strategy in deep-sea chemosynthetic symbiosis

Hong Kong University of Science and Technology

Researchers conduct deep-sea in situ transplant experiments of Archivesica marissinica at site HM-3 — image:
Researchers conduct deep-sea *in situ* transplant experiments of *Archivesica marissinica* at site HM-3 corresponding to moderate hydrogen sulfide depletion.
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Credit: Provided by HKUST

A research team led by Prof. QIAN Peiyuan, Chair Professor of the Department of Ocean Science at The Hong Kong University of Science and Technology (HKUST), in collaboration with international partners, has made significant progress in uncovering how deep-sea chemosynthetic symbioses cope with environmental change. The findings reveal that metabolic flexibility in the symbionts, coupled with the host's finely regulated population of bacterial symbionts, mutually sustains the host's energy stability. This provides important in situ evidence of how chemosynthetic holobionts at deep-sea cold seeps remain resilient when energy supplies fluctuate and highlights the key role of a tiered adaptation strategy in sustaining the stability of cold seep ecosystems.

Apart from HKUST, the research was conducted in collaboration with the Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (Guangzhou Marine Laboratory), Ocean University of China (OUC), the Institute of Oceanology, Chinese Academy of Sciences (IOCAS), and the University of Calgary in Canada. It represents an important outcome within the framework of two UN Decade Programmes namely "CliMetS" and "MOCSI". The research was recently published in the leading international journal Science Advances, titled “In situ evidence of tiered adaptations buffering a chemosynthetic clam holobiont against environmental sulfide fluctuations”.

In chemosynthetic ecosystems, such as deep-sea hydrothermal vents and methane seeps, hydrogen sulfide is a crucial chemical energy source for supporting biological communities. However, its concentration can fluctuate substantially due to tectonic activity, seepage intensity, and processes such as the anaerobic oxidation of methane in sediments. Direct evidence has long been lacking on how deep-sea symbiotic organisms adapt to such dynamic environments and how hosts and symbionts work together to maintain system stability.

The Haima cold seep comprises seep sites at different developmental stages, providing a "natural laboratory" for studying biological responses to environmental change. The research team focused on a dominant species of deep-sea clam (Archivesica marissinica) at the Haima cold seep and its sulfur-oxidizing bacterial symbionts. By combining deep-sea in situ transplant experiments with in situ sample fixation, the research team conducted deep-sea in situ transplantation studies at two sites HM-3 and HM-2 respectively. The clams were moved from their native sediments into transplantation cages positioned approximately 0.5 m above the seafloor, preventing them from accessing hydrogen sulfide-rich sediment. This setup simulates decreased hydrogen sulfide availability, leading to reduced energy and nutrient acquisition: HM-2 represents severe hydrogen sulfide limitation, whereas HM-3 represents relatively moderate limitation.

By integrating metagenomics, transcriptomics, proteomics, quantitative PCR, in situ hybridization, transmission electron microscopy, and protein structure prediction, the research team elucidated a tiered adaptation strategy in holobiont, encompassing symbiont metabolism, host regulation of symbiosis, and resource transportation.

The study revealed that reduced hydrogen sulfide availability first triggered pronounced metabolic reprogramming in the bacterial symbionts. Transcriptomic and proteomic analyses showed that pathways involved in sulfide oxidation, including dsrAB, aprAB, and sat, were suppressed, whereas the soxXYZ gene cluster associated with thiosulfate oxidation was upregulated. These results indicate that when hydrogen sulfide becomes limiting, the bacterial symbionts can adjust their sulfur-oxidation strategies and potentially enhance their capacity to utilize thiosulfate, thereby maintaining energy metabolism and carbon fixation. This metabolic plasticity may represent the first line of defense for holobiont in coping with short-term hydrogen sulfide limitation.

The study further demonstrated that host regulation of symbionts changes with the severity of hydrogen sulfide limitation. Under the relatively moderate hydrogen sulfide limitation at HM-3, the abundance of bacterial symbionts remained stable. Meanwhile, pathways associated with endosomal maturation and endosome–lysosome fusion in the hosts were suppressed, suggesting that the host may reduce intracellular degradation and turnover of bacterial symbionts to help maintain the symbiont population. This reflects that the host preferentially maintains symbiosis under relatively moderate hydrogen sulfide restriction. Under the severe hydrogen sulfide limitation at HM-2, however, symbiont abundance decreased significantly, and transmission electron microscopy revealed the digestion of symbionts by lysosomes. This indicates that hosts facing severe resource constraints might enhance their survival by increasing symbiont turnover to access limited nutrients.

The gill tissue of Archivesica marissinica also possesses a strong sulfur-metabolic capacity and highly expresses key enzymes such as thiosulfate sulfurtransferase (TST). TST participates in the conversion of toxic hydrogen sulfide into thiosulfate, which is then utilized by bacterial symbionts for sulfur oxidation. Coupled with the observed upregulation in the symbiotic soxXYZ gene cluster, these findings suggest that thiosulfate generated during host hydrogen sulfide detoxification may serve as an alternative energy substrate for the symbionts. This establishes a potential metabolic synergy between host detoxification and symbiont utilization, offering new insights into how hosts and symbionts achieve metabolic complementarity under resource-limited conditions.

Additionally, the research team investigated the potential role of Archivesica marissinica hemoglobins in gas transport. The two hemoglobin subunits, Hb1 and Hb2, are primarily localized in blood cells and highly expressed in the foot and gill tissues. Both protein structural prediction and molecular docking results revealed that the hemoglobin complex exhibits a slightly higher binding affinity for hydrosulfide than for oxygen. These findings suggest that the hemoglobin complex may mediate the binding and transport of hydrogen sulfide and oxygen, providing new molecular insights into the mechanisms underlying gas transport in vesicomyid clams.

Prof. QIAN Peiyuan, co-corresponding author of this study, said: "Taken together, we believe that Archivesica marissinica and its symbionts form a multi-layered, tiered adaptation strategy. This enables the deep-sea chemosynthetic holobiont to maintain normal functions and survive while adjusting resource allocation according to the severity of environmental stress. The in situ experimental framework established by this research provides a new approach for investigating the authentic molecular responses of organisms inhabiting extreme deep-sea environments to natural environmental changes. It also offers new scientific evidence for understanding how global deep-sea cold seep ecosystems respond to environmental change and maintain ecological functions and biodiversity."

The co-corresponding authors of this paper include Prof. QIAN Peiyuan (HKUST, Guangzhou Marine Laboratory), Prof. SUN Jin (OUC), and Prof. Casey HUBERT (University of Calgary in Canada). The co-first authors include Dr. LAN Yi (HKUST, Guangzhou Marine Laboratory, University of Calgary in Canada), Dr. YAN Guoyong (HKUST, Guangzhou Marine Laboratory) and Dr. WANG Hao (Guangzhou Marine Laboratory, IOCAS).

Journal

Science Advances

DOI

10.1126/sciadv.aed8728

Method of Research

Experimental study

Subject of Research

Animals

Article Title

In situ evidence of tiered adaptations buffering a chemosynthetic clam holobiont against environmental sulfide fluctuations

Article Publication Date

2-Oct-2026

Researchers conduct deep-sea in situ transplant experiments of Archivesica marissinica at site HM-2 corresponding to severe hydrogen sulfide depletion.

The research team conducts deep-sea in situ transplant experiments of Archivesica marissinica at the Haima cold seep.

The research team analyses hydrogen sulfide binding capability of clam host hemoglobin.

Electric vehicle batteries get a longer lifespan when weak cells are bypassed

Chalmers University of Technology

image:
Photo Ivan Radic licensed under CC BY 2.0.
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Credit: Photo Ivan Radic licensed under CC BY 2.0.

In today's electric vehicle batteries, a single weak cell can limit the life of the entire battery pack, even when the other cells are still working well. The goal is for future batteries to be able to bypass weak cells and make better use of the remaining capacity. A study, led by researchers at Chalmers University of Technology, in Sweden, now shows that a new ‘smart battery architecture’, under optimal conditions, can give electric vehicle batteries over 20 percent longer life in certain vehicles. At the same time, the total cost can be reduced over the battery's lifetime.

Battery packs in electric vehicles, or EVs, consist of many interconnected cells that do not age in the same way. In today's battery structure, the weakest cell can therefore set the limit for the entire package.

Albert Škegro, a doctoral student at the Department of Electrical Engineering at Chalmers University of Technology in Sweden, draws an analogy, describing the structure as the cells being connected by a rope, while they all try to move forward.

"Since they are bound to each other, everyone has to keep the same pace as the slowest cell and stop when that cell stops. With the solution in our study, the battery can instead bypass the cell that is causing problems and continue forward," says Albert Škegro, first author of the new study, which has been published in Nature Communications and conducted in collaboration with industry.

Previous research has shown how important differences between cells can be for the performance and lifespan of EV batteries. In a recently published study, co-authored by Chalmers researcher Changfu Zou, the researchers found that the weakest cells clearly limit the entire battery pack.

A battery that can adapt as cells age

In the new study, the researchers map the benefits of so-called reconfigurable battery packs, where switches and control systems can change the connections between the cells. These battery packs can bypass weaker cells so that more of the remaining capacity can be utilised.

In the researchers' models, the most advanced solution – where each cell can be controlled separately – can extend the lifespan by over 20 percent in some high-voltage vehicles, such as electric trucks and long-range electric cars. In practice, groups of cells are more likely to be controlled together, so the figure is a theoretical upper limit.

"Reconfiguration is not a question of 'on or off'. It is a spectrum, and where a manufacturer chooses to sit on that spectrum determines how much of the potential benefit can be realised," says Changfu Zou, Professor at the Department of Electrical Engineering at Chalmers and co-author of the study.

Longer lifespan can outweigh higher cost

To illustrate what the results can mean in practice, the researchers analysed an example with a typical 80 kilowatt-hour car battery and 12,000 kilometres of annual mileage. The example assumes that a conventional battery pack is replaced after 10 years, in line with current industry practice. In the model, the reconfigurable pack reaches the same point after about 11 years, so roughly 14 months longer. It also had a higher residual value because it had deteriorated less through aging.

"For a private electric car owner, it is a great advantage that the car's battery lasts longer. For a fleet with hundreds of battery packs, extending the battery life can mean significant savings," says Albert Škegro.

The technology is not yet available in series- or mass- produced vehicles but has been tested in research and industrial prototypes. Since it requires additional electronics, the technology has a higher initial cost, but the researchers also show that a longer service life and higher residual value can outweigh the additional cost under many realistic conditions. The potential is greatest in high-voltage vehicles with a long range and many series-connected cells.

In addition to the increased battery life, the researchers also point to more sustainability gains. Today, considerable resources are spent on testing and matching cells with similar characteristics during manufacturing. The new technology allows greater variation between cells and could therefore reduce the need for such precise matching. A larger part of the battery packs can also be given a second life, for example, as stationary energy storage.

"A battery pack that is taken out of service prematurely means both wasted material and wasted energy. Keeping battery packs in use for longer is therefore a sustainability argument even before you take the economy into account," says Albert Škegro.

More about the research:

The study System-level assessment of dynamic reconfiguration for lifetime and cost outcomes in electric vehicle battery packs | Nature Communications, published in Nature Communications.

The authors are Albert Škegro, Torsten Wik and Changfu Zou at Chalmers University of Technology; Bo Bijlenga at PHINIA Inc, Åmål; and Alexander Bessman at Scania CV AB, Södertälje.