In the deep ocean, brown algae and diatoms synthesize a complex polysaccharide called fucoidan, which forms their protective outer layer and can transport carbon to the seafloor for long‑term storage. The molecule’s structure is highly heterogeneous, containing dozens of linkages and branching patterns, making it resistant to degradation by any single microbe. For years, scientists only knew of bacteria that could cleave fragments of fucoidan, leaving open the question of whether a microbial community could break it down completely.
A new open‑access study published in Nature—led by Andreas Sichert (ETH Zurich) and Otto X. Cordero (MIT)—answers this question. The team enriched a fucoidan‑degrading community from coastal seawater and isolated eight bacterial strains that together harbor more than 453 distinct genes, each encoding an enzyme capable of acting on fucoidan. None of the strains alone can fully degrade the polymer.
Using a rapid mass‑spectrometry method, the researchers tracked the consumption of individual sugar monomers and identified two functional roles: some strains specialize in degrading the fucose‑rich backbone, while others target side‑chain sugars such as xylose and galactose. When strains with complementary roles were combined, degradation became synergistic—far exceeding the sum of their individual activities. The more complementary the sugar preferences, the stronger the effect, and certain pairings approached complete breakdown of the polysaccharide.
Surprisingly, this division of labor rendered the system highly predictable. The authors built a simple model that classifies bacterial activity into two broad categories—fucose versus side‑chain sugars. Trained on data from communities of one to three strains, the model accurately predicted degradation in communities containing up to seven strains and generalized to nine structurally distinct fucoidans from other algae.
The study introduces the concept of “diversity‑limited degradation”: without the right combination of complementary specialists, fucoidan persists longer in the ocean, contributing to long‑term carbon sequestration. For biotechnology, the implication is clear—rather than engineering a single “super‑bug,” assembling teams of microbes with complementary capabilities may be a more effective strategy for processing brown‑algal biomass and other complex polysaccharides.
The broader significance lies in demonstrating that even systems with hundreds of uncharacterized enzymes can be reduced to a few measurable traits, enabling simple models to predict community function. This approach could be applied to other recalcitrant biopolymers and offers a new lens on how ecological functions are distributed across multiple organisms.
Review: The work highlights the power of microbial teamwork, turning genomic complexity into a tractable predictive framework and opening new avenues for understanding and harnessing ocean carbon cycling.