Is our microbiome manipulating us to look out for itself?

Links between our gut and our brain, especially via the vagus nerve, can regulate stress disorders such as depression and anxiety. Growing evidence shows that the microbes in our gut can influence this by releasing various neurotransmitters (like dopamine and serotonin) near the rich bed of nerve endings that surround the gut. A lactobacillus found in Yoghurt can alter the GABA inhibitory neurotransmitter system and reduce stress induced behaviors in mice, an effect that requires the intact vagus nerve. I would suggest you have a look at Zimmer's summary of work suggesting that gut bacteria, in addition to helping to break down our food, fight off infections and nurture our immune system, might be a puppet master altering our food preferences to benefit themselves. In mice, bacteria can alter levels of hormones that govern appetite. Possibly they could influence various food cravings in humans.