Identifying the enzymes that break down fucoidan, opening up new possibilities in biomedicine and marine biorefining

The challenge

Fucoidan is a complex polysaccharide found in the cell walls of brown seaweeds, which are widespread throughout the oceans and play a crucial role in regulating the global climate. Because fucoidan is exceptionally resistant to bacterial breakdown, carbon captured by seaweeds through photosynthesis can remain stored in the sea for long periods, helping to reduce atmospheric CO₂.

Until now, however, little was known about how marine bacteria recycle the carbon contained in fucoidan. This made it difficult to estimate how long that carbon remains in the oceans before returning to the atmosphere—an essential question for understanding the role of blue carbon in addressing climate change.

The solution

A research team led by AZTI isolated two bacterial strains from the microbiome of a brown seaweed that can break down different types of fucoidan.

The discovery, published in Nature Communications, also identifies the enzymes responsible for this breakdown, providing new insights into how bacterial communities affect carbon storage in marine ecosystems.

The study sheds light on the mechanisms bacteria use to break down one of nature’s most complex and bioactive polysaccharides, with implications for both climate science and biotechnology.

The results

• New knowledge about the carbon cycle and CO₂ sequestration in marine seaweed ecosystems.
• Better estimates of global blue carbon flows and how long carbon remains in the oceans.
• New avenues for innovation:
  • Fucoidan has bioactive properties with considerable potential for the pharmaceutical industry, including anti-inflammatory, anti-tumour and immunomodulatory effects. Its complex and variable chemical structure, however, makes it difficult to establish clear links between its composition and therapeutic properties. Identifying enzymes that can break down different types of fucoidan could simplify these molecular structures and make them easier to use in medical applications.
  • These enzymes also have considerable potential for marine biorefineries. They could improve the extraction of valuable compounds and support the sustainable conversion of seaweed biomass into products such as environmentally friendly fertilisers, helping to build a circular economy in the marine sector. This approach is particularly relevant where non-native brown seaweeds such as Rugulopteryx okamurae are spreading along coastlines, harming marine habitats as well as tourism and fishing.

This discovery strengthens AZTI’s position in marine biotechnology and the blue economy. It brings together its expertise in marine microbiology and strategic collaborations with IIS Biobizkaia and the UPV/EHU to advance understanding of the ocean carbon cycle.