Scientists Manipulate the Gut Microbiomes of Mice with Nori Seaweed


Seaweed-eating gut bacteria outcompete established bacteria in the large intestine of nori-fed mice. Favoring one species over others in the gut could help stabilize probiotic bacteria in the gut microbiome.

The gut microbiome contains a vast number of bacterial species. Conventional wisdom therefore states that probiotic supplements have little chance of gaining a foothold.

Now Stanford University researchers have shown that it’s possible to favor the establishment of one bacterial strain over others by manipulating mice’s diet. The researchers also found that it’s possible to control how much a bacterium grows in the intestine by calibrating the amount of a specific carbohydrate in each mouse’s water or food.

Whether taking a probiotic supplement or not, we consume low levels of gut-adapted bacteria throughout our daily lives. However, scientists don’t really know what makes one strain successful over another.

To address this issue, researchers at Stanford University tested whether a dietary boost could give specific bacterial strains an advantage over others in the gut microbiome.

The researchers found a strain of Bacteroides (a common human gut bacterium) that could live off something rarely found in the American diet – nori seaweed. They were specifically looking for bacteria that could eat a carbohydrate found in nori called porphyran. 

The researchers then tried to establish these bacteria in the guts of three groups of mice:

Group 1 and 2 had their natural microbiomes removed and replaced with the naturally occurring gut bacteria from two healthy human donors, each of whom donated exclusively to one group or the other. Group 3 maintained their regular mouse-specific microbiomes.

When the mice were fed a regular diet, the researchers found that the seaweed bacteria could establish to some extent in two of the three groups (one of the groups of mice with human bacteria completely rejected the strain).


However, when the mice were fed a porphyran-rich diet, the results were very different. The bacteria established robustly in all of the mice.

The team also found that they could precisely modulate the population size of the seaweed-eating bacteria by increasing or decreasing the amount of nori the animals ate.

The researchers believe that this amazing breakthrough could be used to make therapeutic microbial treatments a reality with a variety of dietary components and microbes engineered to love eating them.