The Good Gut by Justin Sonnenburg

Author:Justin Sonnenburg
Language: eng
Format: epub
Publisher: Penguin Publishing Group
Published: 2015-03-29T16:00:00+00:00

AN UNSUPERVISED DRUG FACTORY

As the bacteria in the microbiota consume MACs they manufacture, in addition to SCFAs, a huge assortment of molecules. Some of these molecules end up in our circulation and are disseminated throughout our bodies. Many of these molecules can be toxic and are cleared by our kidneys and excreted in urine. (Patients with kidney failure must undergo regular dialysis to rid themselves of these microbiota-produced chemicals.) Some microbiota chemical products resemble drugs and actually replicate the design of our body’s own chemical messengers. Many of these molecules can be absorbed through the intestine and interact with our intestinal neurons, immune cells that reside in intestinal tissue, or can be absorbed into our bloodstream and circulate to the brain. These bioactive chemicals, produced by gut bacteria, bathe our own cells, pass signals to our neurons, and potentially affect our minds. Our microbiota is a drug factory dispensing pharmaceuticals from our gut—with direct access to our brain.

Why the microbiota produces drug-like chemicals is unknown. Perhaps through the action of some of these chemicals our appetite is increased, resulting in more nourishment for our gut bacteria. Perhaps these chemicals serve another as yet undiscovered function within the gut that benefits the bacteria that produce them, such as modulating gut motility or impacting immune function. More studies are needed to understand what these chemicals are doing and to gain a better sense of the trillions of pharmacists that are dispensing them.

We have to remember that these bacteria are not consciously aware and are not designing molecules for the sole purpose of manipulating us. But the following hypothetical situation may help illustrate how modulation of our behavior by bacteria could be reinforced and then become an ingrained facet of our biology.

Imagine a bacterial species that is exceptional at consuming pectin, a polysaccharide that is abundant in many types of fruit, like citrus. While this bacterium is consuming MACs from the citrus you ate, it might experience a mutation in its DNA. These biological mistakes in DNA replication happen quite frequently in bacteria, and in most instances, spell trouble for the microbial owner of the DNA, typically leading to its death. In rare instances, however, such mutations may lead to the generation of an interesting, new molecule. If, by chance, one of the billions of pectin-consuming bacteria makes a new molecule that happens to stimulate your desire to eat citrus, that bacteria just stumbled upon a means to modify your behavior in a way that will benefit it and its progeny.

An important part of this story is that such a series of events is extremely unlikely. Chances are small that a bacterium will make just the right chemical to change your craving for citrus, and that the same bacterium will profit when fruit is eaten (i.e., also be a good pectin utilizer). But considering the eons over which we have coevolved with microbes, the trillions of microbial cells within each of us that replicate their DNA every thirty to forty minutes, and the billions of humans on the planet, odds are that a microbe will hit the jackpot occasionally.

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