How to build a de novo synthetic community? Several studies focussed on intercellular metabolic interactions, which can be realised in very different ways . For example, auxotrophic strains have been grown together with complementary metabolic functions . Phototrophic organisms like cyanobacteria are at the basis of light-driven microbial communities and facilitate sustainable growth with heterotrophic partners like bacteria and fungi. Several studies successfully established two-species consortia consisting of a cyanobacterium, engineered to secrete sucrose, feeding a heterotrophic microorganism, bacterium or fungus . Beyond metabolism, many intercellular interactions in microbial communities are mediated by signalling molecules. In bacteria this mechanism is called quorum sensing and allows them to sense their environment and communicate with neighbours. This simple bacterial communication system can be engineered in a modular fashion and has been exploited extensively for rational design . For example, an E. coli strain has been created that is able to communicate with P. aeruginosa and respond by turning on a self-lysis kill-switch . Many opportunities exist to extend these approaches for cooperative intercellular interactions.