Introduction to Bacteroidetes

In this blog post, we are going to look into a phyla (group) of bacteria that are found in all humans and most (if not all) mammals, although their abundance varies. This is the phylum of Bacteroidetes, a very diverse and typically beneficial group of bacteria that live in your gut. Interestingly enough, there are no humans alive that have no Bacteroidetes in their guts. This suggests that at least some of the bacteria in this group are required for the human body to function. Let's get into the basic details of what these bacteria do and how they work:

What are Bacteroidetes?

Bacteroidetes are one of the most common phyla of bacteria that live in your gut. On average, 50% of an individual’s gut bacteria fall into this phylum. However, this number varies based on what diet you follow and where you live. For example, Westerners have many more Bacteroidetes than people from other parts of the world.

Where in the gut are they?

These bacteria are typically found in the distal gut. This basically means that they live on the far end of your digestive tube. However, a few special types of Bacteroidetes can also live in places like your mouth.

What role do these bacteria play?

These bacteria are specialized to break down carbohydrates. Most commonly, the carbohydrates they break down are fibers, which our digestive system cannot break down without help. These bacteria use two diverse classes of enzymes to accomplish this, called glycoside hydrolases, polysaccharide lysases. Bacteria in this phylum can have 100s of types of these enzymes!

If the carbohydrates can’t get into the cell due to size, then these enzymes are secreted by the bacteria to break them down into smaller sizes. After the fibers are taken into the cell, they are converted into short chain fatty acids (SCFAs). Some of these fats are used by the bacteria but most of them are released and absorbed into our body. For people that eat a fiber rich diet, up to 10% of their calories can be coming from this SCFA production.

Specialization

Bacteroidetes are also very special because of how diverse their gene expression is. Based on the conditions in your gut, these bacteria can change the source of energy they use by switching on and off genes. As a result, this phylum of bacteria can stick around inside you regardless of your diet.

Within the phylum, these bacteria are classified into sub groups (called genera). Based on the diets you eat, different sub groups may thrive more than others. In the case of human microbes, three genera of the phylum Bacteroidetes are relevant: bacteroides, prevotella, and porphyromonas. The genera of prevotella is much better at surviving in the guts of non-Westerners who eat more plants, for example. Additionally, porphyromonas is the genera most commonly found living in the moths of humans, helping digest recently ingested food.

Conclusion

Baceroidetes is a very diverse phylum of bacteria, essential for your well being. The bacteria within this group specialize in digesting carbohydrates that are difficult or impossible for your body to digest alone. Since there are countless carbohydrates in the world, there are countless specialized Bacteroidetes present in your gut. Each strain of these bacteria are responsible for digesting a slightly different type of carbohydrate.

In return for the service of digestion, Bacteroidetes get a comfortable place to live, protected from the outer world. This symbiotic trade has been happening for so long that neither you nor the bacteria in your gut can live without the other. So next time you sit down to eat, try to eat a little fiber as a thank you gift for the little microbes working so hard to keep you alive.