Minimal reaction sets for Escherichia coli metabolism under different growth requirements and uptake environments

A computational procedure for identifying the minimal set of metabolic reac tions capable of supporting various growth rates on different substrates is introduced and applied to a flux balance model of the Escherichia coli met abolic network. This task is posed mathematically as a generalized network optimization problem. The minimal reaction sets capable of supporting speci fied growth rates are determined for two different uptake conditions: (i) l imiting the uptake of organic material to a single organic component (e.g., glucose or acetate) and (ii) allowing the importation of any metabolite wi th available cellular transport reactions. We find that minimal reaction ne twork sets are highly dependent on the uptake environment and the growth re quirements imposed on the network. Specifically, we predict that the E. col i network, as described by the flux balance model, requires 224 metabolic r eactions to support growth on a glucose-only medium and 229 for an acetate- only medium, while only 122 reactions enable growth on a specially engineer ed growth medium.