We are not alone. As this enlightening video published by Huffington Post journalist Jacqueline Howard shows, we are walking ecosystems, as our bodies are colonised from top to bottom by microbes that, not happy with behaving like guests, are actually integrated into our biology. “They help us digest food, shape our immune system, alter our metabolism and evidence is even starting to show that they affect the nervous system, influencing our mood and behaviour,” explains Justin Sonnenburg, a microbiologist at Stanford University (USA) in this video. Five essential minutes that will answer many of your questions about the microorganisms we carry around.