Introduction to Proteobacteria

This blog post will look into another interesting and influential phylum of bacteria which populate your gut: Proteobacteria. This group of bacteria is special because while it is not the most populous phylum (5% of microbiome in healthy individuals), it carries the majority of genes in the entire microbiome. This diversity makes this phylum of bacteria incredibly good at living in varied conditions and adapting to change. Perhaps they are too good at this, as we will see later in this post.

What are Proteobacteria?

Proteobacteria are a phylum of bacteria that are not unique to the human gut. The ability of these bacteria to adapt to different environments and food sources has enabled them to live almost everywhere. They live in the soil, the air, in bodies of water, on your skin, and on your gut. These bacteria are a critical component of your microbiome when in check; they are able to regulate the internal environment for the rest of the microbiome population.

Developmental Benefits

Proteobacteria are one of the first bacteria to colonize the neonatal gut. This is essential because Proteobacteria are facultative anaerobes. This means that Proteobacteria prefer to use oxygen to make energy when possible but can also switch to anaerobic metabolism if needed. Both Bacteroidetes and Firmicutes cannot do this, they rely on an oxygen free environment to thrive. When a person is born, their GI tract has very high levels of oxygen. When the Proteobacteria come in, they use up all of this oxygen and change the pH of the gut, making the conditions favorable for the other phyla. Once the oxygen is used up (within the first month), these bacteria switch to anaerobic respiration and shrink in population, stabilizing at 5% of the microbiome.

Proteobacteria Blooms in Later Life

In healthy people, these proteobacteria hang out in the gut without making much fuss, helping metabolize complex molecules as they encounter them. However, decisions people make can dramatically affect this phylum’s prevalence. And these changes can have massive health effects.

Dietary Habits

One potential source of a Proteobacterial bloom is the use of artificial sweeteners. Due to the ability of these bacteria to metabolize all kinds of molecules, Proteobacteria can use artificial sweeteners to reproduce while your and your other bacteria can’t. Another source of Proteobacterial growth is eating a low fiber diet; this type of diet makes it harder for the carbohydrate-favoring Bacteroidetes and Firmicutes to grow. Slowly, the Proteobacteria begin to outcompete these phyla and grow in number.

Either way, this results in an increased number of Proteobacteria in your gut. After these bacteria increase in numbers enough, they trigger an inflammatory response from your body as it tries to control the population. As a part of the inflammatory response, your body produces molecules called nitrates. Unfortunately, Proteobacteria are one of the few phyla of bacteria in your gut that can use this molecule as energy.

As a result, this immune response does the opposite of what it was supposed to do; the Proteobacteria grow even faster and take over more of the gut space. This positive feedback loop generates a chronic inflammation in the gut, which is known to contribute to disorders such as IBS and metabolic syndrome. Disruptions of healthy microbiomes like this can be difficult to quickly resolve after the pattern has been set.

Studies with fecal transplants are currently being done to see if it is possible to control the population of the microbiome by integrating new bacteria directly into the gut. Alternatively, it may be helpful to increase the proportion of fiber in one’s diet. In theory, this should provide nutrition to the Bacteroidetes phylum and enable it to regain some of the territory it has lost to the Proteobacteria bloom.

Conclusion

Proteobacteria is a unique phylum of bacteria that plays the role of environmental regulator in your gut. Without them, it would be difficult for other bacteria to colonize and survive in our guts. Unfortunately, changes in the modern diet have made it very easy to throw Proteobacterial growth out of equilibrium. These changes can have long lasting negative effects if left unchecked over time. While it is true that people genetically prone to inflammation may have a harder time combatting Proteobacterial blooms, everyone can take basic steps to maintain their microbiome. Moderating artificial sweetener consumption and increasing fiber in one’s diet is a good start to maintaining a microbiome that you can live with throughout your life.