Bacteria have been discovered in our guts that depend on one of our brain chemicals for survival. These bacteria consume GABA, a molecule crucial for calming the brain, and the fact that they gobble it up could help explain why the gut microbiome seems to affect mood.
Photo by Custom Medical Stock Photo/SPL. Image of Lactobacillus rhamnosus bacteria under a microscope sourced from New Scientist. Available at: https://images.newscientist.com/wp-content/uploads/2016/07/01134944/c0151529-lactobacillus_rhamnosus_bacteria_sem.jpg?width=700