Cartoon illustration of a model presented by Sewell, Han and Qi (this issue). The “blue river” illustrates the intestine of a host animal, where commensal E. coli (green character) secrete enterobactin (Ent, yellow triangle) and use it to fetch iron (red ball). The host cell (“fisherman”) can also use Ent to obtain iron through the interaction with ATP synthase alpha subunit (ATPS-alpha, fishing pole). Concept by Bin Qi, Aileen Sewell and Min Han (University of Colorado Boulder, USA); art created by David Deen (USA); image modified by MIC. The cover is published under the Creative Commons Attribution (CC BY) license.