This place is big enough for both of us

Complex relationships between bacteria and multicellular eukaryotes have evolved in several environments but science has traditionally focused on interactions that are pathogenic. Recently there has been increased recognition of symbiotic interactions that benefit both the microorganism and the host. The bacterial partner commonly produces essential nutrients that are not synthesized by the host. In return, bacteria benefit from an ample supply of growth materials and environmental stability inside the host. An array of recent genome papers examining microbial symbionts in hosts ranging from insects and worms to plants, has shed light on the genetics that underpin these metabolic partnerships.