Fig. 4.

Viability of CoSMO. Monocultures of the two strains were washed free of adenine and lysine, and mixed at time 0. (A) CoSMO is viable under a wide range of initial partner ratios. The two strains were mixed at the indicated R_→L^←A:Y_→A^←L ratios (R₀:Y₀) and at the same total initial cell density and culture volume (≈5 × 10⁵ cells per ml × 2.6 ml = 1.3 × 10⁶ cells per culture, four replicate cultures per condition). Plots show culture turbidity in OD₆₀₀ (optical density at 600 nm) over time. OD₆₀₀ of 1 corresponds to a population density from 1 × 10⁷ to 5 × 10⁷ cells per ml depending on the cell size. (B) Stochastic CoSMO behavior close to the initial-density requirement. Three replicate cultures (≥20 ml) were set up at 1.1 × 10⁴ cells per ml per strain. Plots show the dynamics of live R_→L^←A (red), live Y_→A^←L (green), dead (gray), and total (black) cell densities. One of the cultures was inviable (I), whereas the other two were viable (II and III).