Figure 7. Cell growth into open space is required for self-organization and cheater isolation.
In an unperturbed spatial environment, a community starting from a high-density (∼105 total cells/mm2) confluent inoculum expanded to new territories (purple). Compared to ‘Center’, self-organization was significantly more in ‘Expanding front’. Consequently, the initially 1:1 : ratio changed in favor of cooperators as the community expanded outward but not in ‘Center’. Sections were collected from three independent communities. Using the Mann–Whitney U-test, the association indexes of the ‘Center’ and of the ‘Expanding front’ were significantly different (p = 4 × 10−4). Exp: experiment.
Figure 7—figure supplement 1. Vertical cross-sections of communities started from a high-density inoculum.
A schematic diagram (A) shows positions (gray solid lines) of cross-sections (B–E) taken from a community initiated from a high-density inoculum (dashed circle). Vertical cross-sections in (B) and (C) were 100 μm and 180 μm from the edge of the community, respectively. (D) and (E) show respectively the center portion and the expanding front portion of a vertical cross-section through the initial inoculum region. Cheater patches became smaller or disappeared as the community front expanded out. Scale bar: 200 μm.