In the global carbon cycle, microorganisms have evolved various methods for fixing carbon. Researchers from Bremen and Taiwan have investigated the methods utilized at extremely hot, acidic, and sulfur-rich hydrothermal vents in shallow waters off the island of Kueishantao, Taiwan. A team led by 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.

Life at the edge: microbial survival in shallow hydrothermal vents

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 seawater chemistry, resulting in extreme conditions.

The rTCA cycle: a metabolic shortcut for energy efficiency

„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.

Tracing carbon flow through the ecosystem

„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.

Implications for understanding ocean-floor ecosystems

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.

MARUM produces fundamental scientific knowledge about the role of the ocean and the seafloor in the total Earth system. The dynamics of the oceans and the seabed significantly impact the entire Earth system through the interaction of geological, physical, biological, and chemical processes. These influence both the climate and the global carbon cycle, resulting in the creation of unique biological systems. MARUM is committed to fundamental and unbiased research in the interests of society, the marine environment, and in accordance with the sustainability goals of the United Nations.

Original publication: BG – The energy-efficient reductive tricarboxylic acid cycle drives carbon uptake and transfer to higher trophic levels within the Kueishantao shallow-water hydrothermal system