Are we on the cusp of a new approach to healthy living and treating disease? BBC Health and Science correspondent James Gallagher explores the latest research into how our second genome, the vast and diverse array of microbes that live on and in our bodies, is driving our metabolism and our health. Recent DNA analysis by the Human Microbiome Project detailed the vast and diverse array of microbes in and on our body - bacteria, archaea, fungi and viruses. It has been described as our second genome - a source of huge genetic diversity, a modifier of disease, an essential component of immunity, and an "organ" that influences not just our metabolism but also our mental health. Unlike the human genome which is fixed at birth, this "second genome" can be manipulated in many ways. Researchers have suggested that our gut microbiome has a major role in the development of chronic conditions such as obesity, inflammatory bowel disease and asthma. Now the work has moved onto detailed analysis of the microbes in people with specific problems and measures to change the microbiome. In this major three-part series, James Gallagher investigates the key research shaping our ability not just to read our microbiome and look at predispositions, but to change it for the better. From the ability to manipulate it to stem chronic disease, to the role it plays in determining our health from birth, to its surprising influence on our brain and behaviour - should we now think of ourselves not as self-sufficient organisms, but as complex ecosystems colonized by numerous competing and health-giving microbes? Picture: Probiotic bacteria Lactobacillus, Credit: Dr Microbe/Getty Images Producer: Adrian Washbourne