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Microbes produce neurotransmitters

One of the most amazing facts to come from psychobiotic research is that microbes can produce neurotransmitters, the chemicals that nerve cells in our brain use to communicate. We humans think quite highly of our brain, so the idea that bacteria could usurp the highly evolved chemistry of that pinnacle of protoplasm is shocking. But the data continue to pour in.

The latest, from an all-star team including Jack Gilbert, Rob Knight, Philip Strandwitz and Kim Lewis, finds that Bacteroides fragilis produces γ-aminobutyric acid (GABA), a major inhibitory neurotransmitter. Furthermore, that same GABA is necessary to grow the bacterial strain KLE1738, so naturally these two microbes form a tight bond.

You might assume that neurotransmitters, involved as they are with our magnificent brains, are complex molecules. But they are actually surprisingly simple chemicals that play a major role in all the kingdoms of life. No one is quite sure what good neurotransmitters do for bacteria, but they may act as signalling molecules similar to their job in brains. More enticingly, they may actually be trying to talk to us. The vagus nerve winds down from your brain and connects to all your major organs, including your gut. Are these neuro-enabled microbes attempting to communicate through the vagus nerve? And what are they trying to say?

A lot of the activity of psychobiotic microbes is pretty subtle, using hormones and cytokines, for instance. But using neurotransmitters is really grabbing the brain by its neurons. Are microbes attempting to control our behaviour? Do they squirt out a shot of GABA to make us feel better about eating foods they like?

This study introduces new techniques for discovering novel psychobiotics as well as demonstrating the tight co-dependencies that make microbiology difficult but exciting. We look forward to more studies like this that help us put a name to specific psychobiotics.

Hooray for Large Studies

Researchers know that there is a strong relationship between gut microbes and mood. New research is confirming that storyline and even naming some of the main actors. In a large Flemish study of over one thousand people (that’s right, this is a human study), researchers correlated both depression and quality of life to specific bacteria. Notably, bacteria that produce butyrate were found to be associated with higher quality of life. Butyrate is a short-chain fatty acid that is like ambrosia for the cells lining the gut, and it has even been shown to stop some colon cancers.

They found three microbes, from the genera Faecalibacterium, Coprococcus and Dialister, that were all associated with better health and mood.

Better tools and larger studies are exactly what are needed to advance the field of psychobiotics, so we have a lot to thank the Flemish for!

Doomed by Your Genes?

One of the most inspiring collaborations in the history of medicine was the Human Genome Project. Taking place from 1998 to 2003, it was an enormous international effort to create a map of all the genes in human DNA. With this map in hand, we would surely be able to navigate our way through all the protein and enzymatic pathways that make a human tick. The fervent hope was that by matching up ailments with genetic variations, we would soon discover the root of all diseases.

It was not to be. Although a few genes were found to be associated with disease, the connection was rarely clean. Finding a one-to-one link between genes and disease was the exception, not the rule. Since then, we’ve discovered that the wealth of microbial species in our gut contain a hundred times more genes than our own surprisingly paltry DNA. Genetically, we are mostly microbe! The Human Genome Project, by missing our microbiota, captured only a tiny sliver of our total genetic toolkit.

Tiny microbes turn out to play an outsized role in our health. Friendly microbes provide us with protection against the other far nastier microbes blanketing the planet. They even help us digest our food and provide us with nutrients that feed and heal the cells lining our guts. If you take care of them, they will reward you with a long healthy life. If you don’t, all hell can break loose.

A poorly balanced microbiota is called dysbiotic. Instead of a bustling cosmopolitan bacterial society, a dysbiotic gut is more like an autocracy where a handful of species take over with few counterbalancing microbes. Without pushback from a diverse microbiota, even mild-seeming commensals can become marauding pathogens. When that happens, the mucus layer in the gut starts to get eaten away, and the gut lining can become porous, letting bacteria enter the bloodstream where they get pumped to every organ in the body. That bodily infection leads to an immune response that, over time, can develop into chronic systemic inflammation.

The collateral damage from inflammation is astonishing. It is a scorched earth campaign that can save you – or kill you trying. Inflammation is at the root of almost all chronic diseases, from Alzheimer’s and Parkinson’s to diabetes, heart disease, obesity, autoimmunity, allergies and pretty much all the scourges of mankind. Most of our problems – as well as the probable solutions – come from our microbiota, not our genes. Our lives are at the mercy of our bacterial overlords. We can only fight them for about 100 years before they take us back.

An interesting question is: do our genes affect our microbiota? Is there a human trait that could make you the perfect bacterial host, or is it all the luck of the draw, the microbes you happen to bump in to as you move through life? Recent research from Eran Segal of the Weizmann Institute in Israel has given us the answer to this nature vs. nurture question. It turns out that our human genes account for a puny 2% of our microbial composition.

It’s a little humbling to know our contribution is so meager, but it’s actually a boon. We can’t control our genome – it’s the parental gift we can’t return – but we can control our diet.

Here’s the takeaway: A poor diet leads to an unbalanced, dysbiotic microbiota that can lead to systemic inflammation – the root of most chronic diseases. That’s the bad news. The good news is that we hold the reins. A proper diet rebalances the microbiota, which can protect you from chronic illness. Our genes may not hold much sway over disease, but our will-power definitely does. No more excuses, no more blaming your parents. This one is up to you.


The Upside of Rabies

Rabies is an awful way to die. The bullet-shaped virus, which is transmitted by a bite from an infected animal, doesn’t move through your circulatory system like most pathogens. Instead, it travels exclusively through nerve cells. Unlike a blood vessel, nerve cells don’t pump fluid around. But they do have some flow, courtesy of protein transporters that travel back and forth along the nerve axons. Rabies viruses grab a ride from these transporters, doggedly hopping across synapses and traveling toward the brain. The outcome is dire for the victim, whose muscles will spasm as hallucinations set in and paralysis finally kills them. However, the propensity to travel along nerves makes rabies a wonderful scientific tool to track nerve networks.

This is how Diego V. Bohórquez discovered that intestines can directly sense what is happening in the gut and then can transfer that info to the brain. Using fluorescently tagged rabies vaccines, he was able to follow the neural path from cells lining the gut called enteroendocrine cells as they connected to the “second brain” surrounding the gut. That pathway offers as yet another way that bacteria in your gut can communicate with your brain. Along with the vagus nerve, hormones and immune reactions, this line of communication makes it easier to understand the gut-brain connection.

We know that bacteria can produce a number of neurotransmitters, including dopamine, serotonin and GABA, but this research now shows us how those chemicals can access the brain without needing to breach the blood-brain barrier. As more of these mechanisms come to light, the story of how psychobiotics work their magic becomes clearer every day.