Fibres of intestinal tissue (in red) surround the nerve cells (in green) of the freshwater polyp Hydra. (Credit: Christoph Giez, Dr. Alexander Klimovich)
An ancient animal has revealed one way nerves shape the microbiome and opened a whole new area of research on gut-brain interaction.
Hydras are miniscule freshwater creatures with a tubular body and tentacles. They don’t exactly have a gut or brain, but they do contain a community of microbes and are among the earliest organisms to evolve a nervous system.
Using Hydras, researchers have observed the first proof of the nervous system cooperating with the microbial community. These findings, published in Nature Communications, show how neurons regulate the composition and distribution of microbes.
Freshwater polyp Hydra. (Photo : Dr. Alexander Klimovich)
“Microbes are everywhere. They’re on the body, on the skin, in the gut and the oral cavity, but they follow very strict spatial rules. Yet nobody really knows who controls that spatial organization,” says Thomas Bosch, a senior fellow in CIFAR’s Humans & the Microbiome
program who led the research team at Kiel University.
Bosch’s team found an answer by eavesdropping on the conversations between the “brain” and “gut” in Hydras. Their nervous system communicates with the microbiome through neuropeptides, molecules secreted by nerve cells. These neuropeptides act as an anti-microbial by keeping away unwanted microbes and maintaining a balance of desired microbes. The neuropeptides also organize bacteria along specific areas of the Hydra’s body.
This research shows that this communication goes both ways.
“It’s not only that the microbiome communicates with the microbes on this one side of communication, but on the other side the neurons also actively communicate with the microbiome,” Bosch says.
This relationship was long suspected, but there was no direct evidence. Now, researchers have a purified molecule they can more easily find in other organisms.
Nerve cells (in green) of the freshwater polyp Hydra produce antimicrobial peptides and thus shape the animal’s microbiome. Rod-shaped bacteria can be seen at the base of the tentacles, marked in red. (Credit: Christoph Giez, Dr. Alexander Klimovich)
This study focuses on a specific neuropeptide present in Hydras, but it provides a helpful approach for other organisms. For example, Bosch says medical researchers could begin looking at patients’ neuron populations and whether they produce neuropeptides that send messages to the gut.
“We use our model system to uncover fundamental rules that underlie the basic interactions between microbes and host cells, including neurons, and we strongly believe that important evolutionary inventions are conserved so the same process should take place in humans,” he says.
Bosch has been studying Hydras for 40 years because they offer a unique view into how organisms have evolved. He believes the Hydra shows the nervous system evolved also as part of maintaining the holobiont. The holobiont concept describes plants, animals and humans as microbes and host cells. Therefore, the nervous system evolved not only to control the motor system but also to actively maintaining the microbiome.
This research concept was inspired in part by conversations in the Humans & the Microbiome program, which includes a diverse range of biologists, bacteriologists, immunologists, historians and anthropologists. For Bosch, the next big question is how this communication pathway is organized and identifying the neuron receptors. He hopes that future research will look beyond Hydras to more complicated organisms and how this is connected to the changes that have fuelled the rise in environmental and chronic diseases over the last 50 years.
“We’ll never understand by looking at a single microbe host and studying it in a petri dish,” he says. “It’s a global problem and it needs an interdisciplinary approach to get to the precise factors involved.”
“A secreted antibacterial neuropeptide shapes the microbiome of Hydra” was published in Nature Communications on Sept. 26, 2017.