Summary:
Microorganisms have found remarkable ways to thrive at hydrothermal vents, even in shallow coastal waters where extreme conditions prevail. Off the volcanic island of Kueishantao in eastern Taiwan, super-heated, acidic waters rise from the seafloor, dramatically altering the surrounding seawater chemistry. Despite the harsh environment, these vent systems support dynamic communities of life.
A study led by Joely Maak of MARUM – Center for Marine Environmental Sciences at the University of Bremen, in collaboration with researchers in Taiwan, reveals how a group of microorganisms dominates this environment by using a secret biochemical strategy. The team found that Campylobacteria employ the reductive tricarboxylic acid (rTCA) cycle, a more energy-efficient method of carbon fixation compared to the widely known Calvin cycle.
The research has been published in Biogeosciences.
By analyzing carbon isotopes in fatty acids, the researchers tracked how carbon fixed by these microorganisms moves through the local food web, reaching endemic vent crabs. The findings offer new insights into how chemical energy, rather than sunlight, sustains life in shallow hydrothermal systems.
Microorganisms employ a secret weapon during metabolism
In the global carbon cycle microorganisms have evolved a variety of methods for fixing carbon. Researchers from Bremen and Taiwan have investigated the methods that are utilized at extremely hot, acidic and sulfur-rich hydrothermal vents in shallow waters off the island of Kueishantao, Taiwan.
A team working with first author Joely Maak of MARUM – Center for Marine Environmental Sciences at the University of Bremen has now published their study in the professional journal Biogeosciences.
Extremely harsh conditions can be found even in shallow marine waters. A common cause for this is the presence of hydrothermal systems where dissolved materials from the Earth’s interior make their way to the surface. These systems are usually the only energy source in the deep sea because photosynthesis is not possible in the dark depths.
Hydrothermal vents, however, also occur in shallow coastal regions, for example, near the volcanic island of Kueishantao in eastern Taiwan. The island is surrounded by hydrothermal vents in shallow water, at depths of around ten meters. Hot and acidic water rises to the surface here and alters the sea-water chemistry. This results in extreme conditions.
“These chimneys release super-heated, highly acidic water into the overlying water columns. One might think that such an extreme location is lifeless, but it is actually full of life because at the same time the vents are constantly producing chemical energy in the form of reduced chemical compounds,” says Joely Maak, first author of the study and a PhD student at MARUM.
One of the predominant organisms at these hydrothermal systems is a microorganism called Campylobacteria.
Its “secret weapon”, as Maak refers to it, is the reductive tricarboxylic acid (rTCA) cycle. This cycle is a biochemical pathway for transferring carbon into organic molecules and biomass. Compared to the more widely utilized Calvin cycle, organisms using rTCA do not have to go through as many energy-intensive steps. That is the secret weapon that makes it possible for them to predominate in this extreme environment.
“The analysis of isotope ratios has enabled us to track the carbon fixed using this ‘secret weapon’ even into the crab that lives there – a transfer that could not be detected in this way before,” explains Dr. Solveig Bühring of MARUM, a senior author of this study.
The study is an integral element of research within the current Cluster ‘The Ocean Floor – Earth’s Uncharted Interface’. The main objective here is to gain a better understanding of ocean-floor ecosystems under changing environmental conditions and material cycles.
Journal Reference:
Maak, J. M., Lin, Y.-S., Schefuß, E., Aepfler, R. F., Liu, L.-L., Elvert, M., and Bühring, S. I., ‘The energy-efficient reductive tricarboxylic acid cycle drives carbon uptake and transfer to higher trophic levels within the Kueishantao shallow-water hydrothermal system’, Biogeosciences 22, 7, 1853–1863 (2025). DOI: 10.5194/bg-22-1853-2025
Article Source:
Press Release/Material by MARUM – Center for Marine Environmental Sciences | University of Bremen
Featured image: White waters of Kueishantao: sulfur-rich hydrothermal fluids turn the sea milky.Credit: S. Bühring | MARUM | University of Bremen
