Figure 6. Pathways of which the activation is dependent on the initial state of the cell. Example of a sustainability-PEM that is neither a producibility-PEM nor an optimal-efficiency-PEM.

In the iJR904 network, the production of the biomass component peptido_EC (Peptidoglycan subunit) is assured by a cycle from di-trans,octa-cis-undecaprenyl diphosphate to diphospohdecaprenu-[GlcNAc-MurNAc-pentapeptide]n. All the elements involved in the cycle are sustainability, producibility and optimal-efficiency-PEMs. The cycle is initiated by a pathway starting from pyruvate and composed of nine sustainability-PEMs that are neither producibility nor optimal-efficiency-PEMs. Indeed, at steady state, activation of the initiation pathway is not required for the production of an optimal biomass, although this pathway may be necessary to initiate the cycle when not in a steady state. The latter role in the functioning of the network is reflected by the sustainability property.