Environmental dependence of the activity and essentiality of reactions in the metabolism of Escherichia coli

In cell biology, the concept of essentiality is generally referred to genes. However, it can be extended to reactions due to the fact that the knockout of a gene is translated into the inability of the metabolic network to use the reaction which is under control of the knocked out gene. This allows to compute cores of reactions which are important for metabolism, or to extend the concept of essentiality into superessentiality, a property which will be explained in the following section.