Discover molecular pathways for marine glyco-Carbon sequestration

Project Information

C-Quest

Grant agreement ID: 101044738

DOI

10.3030/101044738

EC signature date 30 September 2022

Start date 1 October 2022

End date 30 September 2027

Funded under

• European Research Council (ERC)

Total cost

€ 2 277 248,00

EU contribution

€ 2 277 248,00

Coordinated by

UNIVERSITAET BREMEN
Germany

Periodic Reporting for period 1 - C-Quest (Discover molecular pathways for marine glyco-Carbon sequestration)

Reporting period: 2022-10-01 to 2025-03-31

Summary of the context and overall objectives of the project

Each year the burning of fossil fuels adds around 10 gigatons of carbon to the ~900 gigatons of atmospheric carbon, fueling the climate emergency. Meanwhile, marine algae fix ~50 gigatons of inorganic carbon via photosynthesis into building blocks of long-chain sugar molecules also known as glycans. The growth of these algae, the aggregation and sinking of algae cells and algae-derived organic material in the ocean plays a central role in carbon dioxide removal from the atmosphere. In this process, known as the biological carbon pump, fixed carbon is moved to depths below 1000m and sediments, where it can be stored for centuries. Key of this process is that the algae material remains stable preventing bacteria from degrading it and releasing carbon back into the atmosphere.

Algae invest up to 80% of their organic carbon into glycans, which are also found in high concentrations in sinking particles and marine sediments, suggesting their substantial role in sequestering carbon at global scale. However, to this day the structural characteristics and quantities of algal glycans relevant in carbon sequestration remain largely unknown due to their immense diversity, which arises from many different building blocks, various connection patterns, branching structures, and chemical modifications. Current analytical approaches do not provide sufficient resolution and bulk concentration measurements blur our view on the role of individual glycans in the process. Our developments of enzyme-based methods to quantify individual glycans and antibody techniques to identify trace amounts of glycans enable us for the first time to structurally describe and quantify individual algal glycans.

In this project, we use and develop these methods further to identify which structures make glycans difficult to degrade and quantify the export of selected glycans via the biological carbon pump. In addition, we investigate the potential co-evolution of algal glycan structures and bacterial enzymes that degrade those glycans. Our insights will help us to understand the role of algal glycans in the global carbon cycle, explore their potential for carbon sequestration and reveal molecular principles that govern carbon sequestration in and beyond the ocean. This will help to understand how and how much the ocean stores carbon, which is key knowledge for managing the climate emergency.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

We developed Glyco-Annotate, a publicly available tool for de novo annotation of glycan compositions for mass spectrometry data, which facilitates the exploration of glycan chemical diversity. Applying this tool, we have found fucose-rich deep-sea oligosaccharides in the North Atlantic Ocean, which suggests their selective preservation in the deep-ocean.

Adapting the techniques of anion exchange chromatography, enzyme linked immunosorbent assay and biocatalytic enzyme-based assay we were able to detect and quantify the complex algal glycan fucoidan. We discovered that brown algae inject significant quantities of fucoidan into the ocean, suggesting carbon sequestration already during the lifetime and independent from algae growth. In addition, we discovered that diatoms inject significant quantities of a previously unknown sulfated mannan, selecting for bacteria with a specifically adapted enzymatic cascade. This sulphated mannan may impose a significant selection pressure on marine microbes worldwide.

Using polysaccharides as bioindicators of carbon sequestration we followed carbon from source to sink in different costal ecosystems. Our research shows that coastal vegetated ecosystems accept, accrete and stabilize carbon from different and distant donors, highlighting their interconnectedness and their contribution to carbon sequestration.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Our results highlight the role of algae and their glycans in the global carbon cycle. The discovery that algae inject significant amounts of the complex algal polysaccharide fucoidan into the ocean indicates carbon sequestration by algae already during their life span, making algae farming even more promising for sequestering carbon. The discovery that the algal glycan fucoidan becomes part of coastal vegetated ecosystems emphasizes the interconnectedness of these systems and highlights the role of rewilding wetland, restoring seagrass meadows and policy makers and stakeholders should think about these efforts in a synergistic way.