The number of active metabolic pathways is bounded by the number of cellular constraints at maximal metabolic rates
Fig 2
Proportionality of reaction rates and growth rates, shown by many microorganisms, is an indication of low metabolic complexity.
Measured uptake rates [28–33] were gathered from experiments in which growth rate was varied in carbon-limited chemostats. For each species we normalized the measured growth rate to the so-called critical growth rate: the growth rate at which the production of overflow products starts. Uptake rates were normalized relative to the uptake rate of the species at the critical growth rate. Up to the critical growth rate, all microorganisms show a simple proportional relation between the growth rate and uptake rates of glucose and oxygen. In Section 8 we explain why this proportionality is an indication of the usage of only one EFM. After the critical growth rate, the reaction rates are no longer proportional, a phenomenon called overflow metabolism.