Fig. 2: Expansion of black box model to include multiple nutrients.

A The overall growth process is split into two reactions – a catabolic process in which free energy is released and an anabolic process in which new biomass is formed. The ring in the middle of the cell represents the coupling of anabolism and catabolism by ATP and other biochemical process. B Schematics of black box model expansion for two degradable nutrients. A catabolic reaction is added for each nutrient. C Schematics of model expansion for a combination of a degradable nutrient and a second nutrient that can only be used as a biomass precursor. The anabolic reaction is separated into two reactions – one for the biosynthesis of the biomass precursor and a second for the rest of the anabolic process excluding the biosynthesis reaction of the biomass precursor. D Black box model prediction for growth on two nutrient sources without mutual effect. The model predicts the produced biomass is a linear sum of the biomass gained from each nutrient. The overall biomass yield, the slope of the curve, is independent of availability of different nutrients.