Fig. 2

Engineering interactions in microbial consortia. A There are six possible pairwise interactions between two strains. These consist of no interactions (1: neutralism), one-way interactions (2: commensalism and 3: amensalism), and two-way interactions (4: mutualism, 5: competition, and 6: predation). Adapted from Kong et al. [25]. (1) Neutralism: Both populations exist with no impact on the other. (2) Commensalism: B benefits from A (i.e., the growth of B is promoted by the presence of A), but A is not affected by B. (3) Amensalism: B is inhibited by A, but A is not affected by B. (4) Mutualism: A and B are mutually beneficial. (5) Competition: A and B mutually inhibit each other. (6) Predation: B benefits from and inhibits A. B Predator strain constitutively expresses toxic ccdB which can be suppressed by ccdA that is induced by QS signal 3OC6HSL expressed by the prey strain using the lux system. The predator strain expresses QS molecule 3OC12HSL using the las system that induces toxic ccdB expression in the prey strain. Adapted from Balagadde et al. [27]. C E. limosum uses a native metabolic pathway to convert CO into toxic acetate. E. coli are engineered to intake acetate and convert it to itaconic acid (ITA) or 3-Hydroxypropionic acid (3-HP). Adapted from Cha et al. [44]. D Two strains expressing orthogonal synchronized lysis circuits. Both strains use quorum sensing to induce cell lysis. They also have competition due to limited space. Scott et al. found the LuxR and RapR quorum-sensing systems could be used orthogonally. Lysis will only be induced in a strain if its quorum-sensing molecule is at a high enough concentration. The LuxR system senses 3-oxo-C6 HSL (3OC6), and the RpaR system senses p-Coumaroyl HSL (pC). This resulted in the two strains coexisting despite different growth rates. Adapted from Scott et al. [26]. E (1) A microbial consortium in a well-mixed culture can have interactions between different populations. Spatial arrangement can decrease the strength of these interactions by controlling (2) the distance between different populations on a surface or (3) separating different populations with a physical barrier. Arrow thickness represents strength of interactions