Figure 5.
Network representation of a cross-feeding chain in which metabolism of y1 by x2 produces a by-product which x1 can metabolize for growth, and this process, in turn, produces a by-product which x3 can metabolize for growth. Note that the production of y2 by x2 only occurs when y1 is present, and the production of y3 by x1 only occurs when y2 is present, so that this chain does not have an effect on other trios involving a subset of three species in the chain. For simplicity, this dependency is not shown, nor is it included in figure 6. (Online version in colour.)