"Microbial genes, brain & behaviour – epigenetic regulation of the gut–brain axis"
http://onlinelibrary.wiley.com/doi/10.1111/gbb.12109/fullInteresting article, just adding to the rapidly growing field of the gut microbiome influence on human health.
Also of note on this subject, when I was at a conference this past week, I listened to a talk/lecture on how the gut microbiota influences the host via modulating certain circadian clock proteins, indicating an even further level of regulation.