How Do Bacteria Drive Our Behavior? A Simple Explanation

Gut Bacteria
(photo credit: Scimat Scimat via Getty Images)

Each creature's personal microbiome can be thought of as its inner ecology, and this microbiome is inextricably linked to the health of its host. While we've known for a long time that bacteria can cause illness and death, scientists have only lately begun to realize that bacteria are also absolutely necessary for health, as our body relies upon the activity of "friendly" bacteria to fulfill basic metabolic functions. Our own bodies even produce chemicals whose only purpose is to feed bacteria, that's how necessary they are to our survival. 

It is now believed that 84% of our body's immune system function occurs in the intestinal tract, directly driven by our gut bacteria. According to mercola.com, key areas of health affected by the microbiome include:

Behavior. A study published in Neurogastroenterology & Motility found that mice lacking in gut bacteria behave differently from normal mice, engaging in what would be referred to as "high-risk behavior." This altered behavior was accompanied by neurochemical changes in the mouse brain.

In fact, your gut serves as your second brain. It produces more of the neurotransmitter serotonin, which is known to have a positive influence on your mood, than your brain does.

Gene expression. A probiotic-rich beverage has been shown to influence the activity of hundreds of your genes to help them express in a positive, disease-fighting way. This makes your gut health a very powerful variable of epigenetics, a cutting-edge field of medicine showing that your lifestyle plays a significant role in your genetic expression.

Diabetes. According to a study from Denmark, bacterial population in the gut of diabetics differs from non-diabetics. According to the authors, the results of their study indicate that type 2 diabetes in humans is linked to compositional changes in intestinal microbiota.

A healthy diet – low in sugar and grains; high in whole raw foods and fermented foods – allows your beneficial gut bacteria to flourish.

Autism. Establishment of normal gut flora in the first 20 days or so of life is critical in appropriate maturation of your baby's immune system. Hence, babies with abnormal gut flora have compromised immune systems and are particularly at risk for developing ADHD, learning disabilities, and autism, especially if they are vaccinated before restoring balance to their gut flora.

Obesity. Probiotics may help fight obesity. Restoring your gut flora is therefore a crucial consideration if you're struggling to lose weight. (mercola.com)

In terms of the "Simple Explanation," the microbiome is one fractal level down from multi-celled organisms like ourselves. The microbiome isn't exactly part of our own "Whoville," because their DNA is different than ours. The relationship is very much like a coral reef, where our Whoville is the coral and the bacteria are the little life forms that live on and in the reef.

In May of 2014, NBC News reported that researchers at Arizona State University had discovered significant differences in bacterial metabolites between children with autism and those without.  They found that seven of 56 metabolites examined were significantly altered in fecal samples from autistic children. Most of the seven metabolites worked as neurotransmitters or controlled neurotransmitter biosynthesis. Study researcher Dae-Wook Kang hypothesizes that the neurotransmitter-related metabolites affect gut-to-brain communication and alter brain function. 

credit: Science News for Students; 5-22-2015

Recent research on mice microbes demonstrates that it is the bacteria that establish the all-important blood/brain barrier that protects our brains from invasive chemicals. In mice raised without bacteria, the missing blood/brain barrier allows unwanted chemicals to accumulate in the brain. (Science News for Students; 5-22-2015) This gives us yet another concrete example of bacteria working on behalf of the host organism's optimal functioning.

Carrying the implications of current research a little further, it makes evolutionary sense for our bacteria to affect our behavior. Bacteria not only affect our moods, they affect the food we reach for to consume. 

When the bacteria is hungry for sugar, we reach for the sugar to feed them. We are carriers for the bacteria. We are their servants. We eat on their behalf, and the food we eat is influenced by the particular mix of bacteria we carry in our guts. "Unfriendly" gut bacteria uniformly prefer a sugary, low-fiber environment. "Friendly" bacteria, on other hand, need a high-fiber environment in which to thrive; eating plant fibers lines our gut with an ideal matrix for the growth of friendly bacteria. Sugar consumption, on the other hand, causes a relative decrease in friendly bacteria and an increase in unfriendly bacteria. The unfriendly bacteria in your gut pressure you to eat sweets so they can survive. No wonder it is so hard to resist sweets! It's your will-power against all of theirs!

Source: http://pathogens.plosjournals.org/perlserv/?request=cover-legend&volume=2&issue=2
Toxoplasma gondii, an obligate intracellular human parasite, has a unique cytoskeletal apparatus that is probably used for invading host cells and for parasite replication. Shown here are images of T. gondii constructing daughter scaffolds within the mother cell. Cyan: YFP-α-Tubulin; yellow: mRFP-TgMORN1 (see Hu et al.).
Credit: Image provided by Ke Hu and John Murray.

We know, for example, that toxoplasma gondii bacteria influences the behavior of infected mice. When a mouse's brain is infected with this bacteria, the mouse is compulsively driven to engage in risky behavior in the presence of cats. This is because the toxoplasma gondii can only reproduce in the guts of cats. Therefore, infected mice must be eaten by cats in order for the bacteria to reproduce. The bacteria drive the mice to be eaten by cats!

According to the University of Cornell, "The life cycle of Toxoplasma gondii is complex and involves two types of host—definitive and intermediate. Cats, both wild and domestic, are the only definitive hosts forToxoplasma gondii. This means that the parasite can only produce oocysts (eggs) when infecting a cat. When a cat ingests an infected prey (or other infected raw meat) the parasite is released into the cat’s digestive tract. The organisms then multiply in the wall of the small intestine and produce oocysts during what is known as the intraintestinal infection cycle."   (http://www.vet.cornell.edu/fhc/Health_Information/brochure_toxo.cfm)

We know the toxoplasma gondii drive the mice to be eaten by the cats. This is undisputable. This is a clear example of the host organism working on behalf of the bacteria. The Simple Explanation of this phenomenon is that the governing Unit of Consciousness of each hungry bacterial colony, the collective bacterial "hive mind,"  exerts the influence of their collective will on the host's decision-making mechanism. They carry a big vote, in other words, that may or may not be at odds with the host body's own will. 

Would it be entirely out of the realm of possibility for bacteria to have been responsible for human-scale historical trends? How about the bacteria's need for refined sugar driving the slave-trade that labored on their behalf in the sugar plantations? Chew on that one for a while!