After you build a model, the next step is deciding which exchanges you need to include for the in silico organism to produce biomass, or grow. Depending on how fastidious the organism is, this can range from all amino acids, glucose, O2, a Lexus, and 60-year pension to little more than salts, H2O and CO2.
What the Flux?
Each reaction in the model will have a flux ranging from -1000 to 1000. The flux values are given in the units of mM/gDCW*hr-1. By definition, a milimole of Biomass is one gram dry cell weight, therefore a direct relation to coefficient of exponential growth curve. These values can be compared and evaluated in this fashion.
After entering exchanges, attempt to run the FBA equation to solve for maximum biomass flux. This value should be positive and within a logical range, according to actual growth rate data.