Fig. 1.

Rational design of CoSMO. (A) Overproduction of metabolites is required for viable cooperation. At time 0, monocultures of indicated strains grown in synthetic dextrose medium (SD) with the required adenine or lysine supplement (37) were washed free of supplements and mixed. Plots show population dynamics of fluorescent live R (red), fluorescent live Y (green), nonfluorescent dead (gray), and total (black) cells of the coculture as measured by flow cytometry (Methods). (II) Data from three replicate cultures are superimposed. (B) The “wiring” diagram of CoSMO. CoSMO consists of two yeast strains: R_→L^←A, which lacks Ade8 enzyme and harbors Lys21^op enzyme, and Y_→A^←L, which lacks Lys2 enzyme and harbors Ade4^op enzyme. Cells lacking Ade8 (Lys2) cannot synthesize adenine (lysine) and therefore require intake (^←) of the corresponding metabolite. Ade4^op and Lys21^op are no longer sensitive to end-product feed-back inhibition and consequently overproduce (^op) the corresponding metabolite that is eventually released (_→) into the medium (25, 26). Crosses represent genetic inactivation; yellow bars and arrows represent losses and gains in metabolite synthesis, respectively.