Metabolic reaction rates are an important phenotypic characteristic of microbial cells. ese rates (from here on also termed “uxes”) are a function of the environment and genetic code of the cell. Metabolic ux analysis aims at determining changes of uxes in response to changes in the environment (e.g., different carbon substrates) or gene deletions or insertions. Metabolic uxes can only be calculated in case the stoichiometry of the biochemical pathways in which the uxes are to be determined is known. is stoichiometric information is typically organized in a systematic linear algebraic format to give mass balances of all intracellular metabolites:

d t

dt t

X S v

( ) = ⋅ ( ) (20.1)

where X is the vector containing all intracellular metabolite concentrations, S is the time-invariant stoichiometry matrix and v is a vector containing all reaction rates.