Scientists Find Marine Bacteria that Break Down a Key Compound for the Carbon Cycle and Global Climate

• A Spanish research group has identified bacteria associated with brown macroalgae capable of degrading fucoidan, a complex polysaccharide essential for carbon storage in the oceans.
• This discovery provides new insights into the carbon cycle and CO₂ sequestration in marine ecosystems, as well as opening the door to innovations in biotechnology, biomedicine and biorefining.
• The research, funded by the Basque Government’s Elkartek programme, has been coordinated by the AZTI technology centre in collaboration with the IIS BIOBIZKAIA Institute and the University of the Basque Country (UPV/EHU).

Sukarrieta, 13 February 2025 – Fucoidan is a complex polysaccharide found in the cell wall of brown algae, organisms that are widespread in the oceans and play a key role in regulating global climate. This compound, when released into the marine environment, is exceptionally resistant to bacterial degradation, allowing the carbon sequestered by these algae through photosynthesis to be stored in the oceans for long periods of time. This process contributes to the reduction of carbon dioxide (CO₂) in the atmosphere. However, knowledge of how marine bacteria influence the recycling of carbon from fucoidan remains limited.

A recent study published in Nature Communications has isolated two bacterial strains from the microbiome of a brown macroalga capable of degrading different types of fucoidan. This scientific breakthrough provides new insights into the role of bacterial communities in the efficiency of CO2 capture by marine ecosystems. In addition, the discovery of the enzymes responsible for this degradation opens the door to biotechnological applications in sectors such as biomedicine and biorefining. 

Impact on carbon cycle and climate change

Underwater macroalgal forests sequester significant amounts of carbon, comparable to terrestrial ecosystems such as the Amazon rainforest. According to Laura Alonso-Sáez, the researcher who coordinated this research and a member of the AZTI Technology Centre, ‘our work shows that some bacteria in the macroalgae microbiome can have an impact on the amount of carbon sequestered in marine ecosystems, with implications at the climate level. In addition, we have been able to better understand the mechanisms used by bacteria to degrade one of the most complex and bioactive polysaccharides found in nature, which could have implications in fields such as biotechnology and biomedicine.

The rate of microbial decomposition of fucoidan is a key factor in determining how long carbon remains stored in the oceans before being returned to the atmosphere. Understanding the mechanisms behind this process is essential to improve current estimates of global carbon fluxes and to better predict the impact on marine ecosystems known as ‘blue carbon’.

Biotechnological applications of fucoidan and its enzymes 

Fucoidan also has bioactive properties with high potential for the pharmaceutical industry, including anti-inflammatory, anti-tumour and immunomodulatory effects. However, its complex and variable chemical structure makes it difficult to establish clear relationships between its composition and its therapeutic properties. The identification of specific enzymes capable of degrading different types of fucoidan could simplify these molecular structures and facilitate their use in medical applications.

On the other hand, these enzymes have great potential for marine biorefining. They could optimise the extraction of valuable compounds and promote the sustainable conversion of algal biomass for different uses such as, for instance, green fertiliser, thus promoting a circular economy in the marine sector. This approach is particularly relevant in the face of problems such as the invasion of coastal areas by non-native brown algae such as Rugulopteryx okamurae, which negatively affects both marine habitats and economic activities related to tourism and fisheries.

Citation: Pérez-Cruz, C., Moraleda-Montoya, A., Liébana, R. et al. Mechanisms of recalcitrant fucoidan breakdown in marine Planctomycetota. Nat Commun15, 10906 (2024).
https://doi.org/10.1038/s41467-024-55268-w