For Brain Awareness Week, Dr Phil Burnet (Department of Psychiatry, University of Oxford) speaks about how the gut microbiome can affect mood and mental health. Part of the Bacterial World exhibition programme (www.oum.oxac.uk/bacterialworld). Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales; http://creativecommons.org/licenses/by-nc-sa/2.0/uk/