A special type of seaweed-eating bacteria found in the human gut could be used to treat serious illnesses like kidney disease.

These bacteria – called Bacteroidetes – help people to digest the fibres found in seaweed, which are different to those found in things like fruits, vegetables, grains and nuts. However, not everyone has these bacteria in their gut microbiome – without them, you’re not able to break down seaweed found in foods like sushi or Welsh laverbread. It’s unlikely that you’ll feel any negative side effects to their absence, though.

By understanding how these specialised bacteria have evolved, researchers hope to develop gut-friendly bacteria that can be genetically engineered to perform as treatments.

Read more about the gut microbiome:

To learn more about these bacteria, scientists at the University of Michigan Medical School tested 354 faecal samples, taken from their undergraduate students. These were then introduced to four seaweed fibres: porphyran, laminarin, alginate and carrageenan.

Laminarin is similar to another group of compounds, beta-glucans, which are more common in cereals like oat, barley, wheat and rye, and in fungi and yeasts. This, the researchers believe, could be why they found the bacteria needed to break down laminarin in many of the samples. The bacteria needed to break down the three other fibre types were rare among their student population, even though carrageenan is found in many processed foods, where it acts like gelatine.

The team then looked at the genetic make-up of the bacteria. Surprisingly, they noticed that it wasn’t just the Bacteroidetes species that was breaking down the seaweed. Another common gut bacteria, Firmicutes, had somehow ‘picked up’ the genes needed to break down the fibres.

“Bacteria in general, and bacteria in the human gut in particular, are very adept at exchanging genes,” said Dr Eric Martens, one of the lead authors of the new study. “They can exchange abilities like [the breakdown of seaweed], but others also. They can exchange antibiotic resistance traits, which is part of the reason why or antibiotic resistance is such a problem.”

Martens says previous studies, such as one in 2010 by a co-author Dr Jan Hendrik Hehemann, show that the human gut bacteria share a common ancestor with a marine bacteria that lives in the ocean and feeds on seaweed there. How the genes from the marine bacteria ended up in bacteria in the human microbiome “remains a mystery”.

“When we sequenced the genomes of these organisms, we a lot of things moving between bacteria. But we don't know how frequently these exchange events happen, and we don't know how these genes get into those [bacteria in the first place].”

A bowl of ramen topped with roasted seaweed
Seaweed is found in many foods, including sushi, ramen (pictured), crispy nori snacks and laverbread © Getty Images

Now, scientists are looking to understand exactly how these gene exchanges happen. The knowledge could offer new treatments, as studies show bacteria can be engineered to carry particular genes into a person’s gut and exchange them with the other members of the microbiome.

“There are really interesting biotechnological applications here,” said Martens. One company utilising the technology is called Novome, which Martens is currently collaborating with. Novome are using a variant of the seaweed-digesting bacteria and genetically engineering it to perform other functions.

Current clinical trials are investigating whether the bacteria could treat a condition called hyperoxaluria, where people can’t properly process oxalic acid, a nutrient found in leafy greens. People who have high levels of oxalic acid will get kidney stones more frequently and can develop chronic kidney disease.

But Novome have genetically-engineered a seaweed-eating bacteria to also hold the gene for processing oxalic acid.

While these engineered bacteria could be given as a probiotic, Martens explains this would rely on the bacteria being able to grow within the gut, competing with all the other bacterial colonies that have been established in your microbiome over a long time.

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“Most over-the-counter probiotics nowadays don’t colonise your gastrointestinal (GI) tract very well, because even if you took a really big capsule for a full of probiotics, you're at most getting 10- to 100-billion bacteria. These are vastly outnumbered by the bacteria that are already in [your gut] and there who are better adapted to being there.”

Instead, Novome are supplementing their engineered bacteria with seaweed, to give it the best chance of colonising. “The seaweed can help the bacteria implant into their GI tract to process the [excess] oxalic acid,” said Martens.

About our expert

Dr Eric Martens runs the Martens Lab at the University of Michigan Medical School, where he and his team further our understanding of the human gastrointestinal tract.


Amy ArthurEditorial Assistant, BBC Science Focus

Amy is the Editorial Assistant at BBC Science Focus. Her BA degree specialised in science publishing and she has been working as a journalist since graduating in 2018. In 2020, Amy was named Editorial Assistant of the Year by the British Society of Magazine Editors. She looks after all things books, culture and media. Her interests range from natural history and wildlife, to women in STEM and accessibility tech.