This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Deep in the ocean, brown algae and diatoms produce a complex carbohydrate molecule called fucoidan, which helps form their protective outer layers. The fucoidan molecule is very difficult for microbes to break down because its chemical structure may include dozens of different linkages and branching patterns that vary from one algal species to another.
This resistance to decay is one reason why fucoidan matters; when microbes struggle to break it down, fucoidan can sink deep into the ocean, carrying carbon with it and potentially storing it for long periods. This could make fucoidan an important player in the ocean's carbon cycle. For many years, scientists knew of individual bacteria that could break down pieces of fucoidan.
But one fundamental question remained unanswered: Could a microbial community break it down completely, and if so, how? A new open-access study published in Nature, led by Andreas Sichert, a former MIT postdoc now at ETH Zurich, and Otto X. Cordero, associate professor of civil and environmental engineering at MIT, provides an answer.
"No single bacterium can finish the job," says Cordero. "Instead, fucoidan is degraded through teamwork. Different bacterial strains specialize in different parts of the molecule, and together, their combined efforts get the job done far more efficiently than any one organism could manage alone." To understand how fucoidan breaks down in nature, the research team enriched a fucoidan-degrading bacterial community from coastal seawater samples.
What they found was staggering: more than 453 different genes, each responsible for making an enzyme that can act on fucoidan, were spread across eight bacterial strains the researchers isolated. On their own, none of these strains could fully break down the molecule. But when the researchers used a new, rapid mass spectrometry method, they were able to observe how bacteria consumed individual sugar building blocks—and a clear pattern emerged.
All of that genetic complexity could be reduced to two roles. Some bacterial strains specialized in degrading fucoidan's fucose-rich "backbone," while others specialized in removing its side branches, which contain less common sugars such as xylose and galactose. When strains playing both roles were combined, something noteworthy happened: Degradation didn't simply add up.
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