Network of minimal pathway maps for E. coli. The box and ellipse nodes represent the conserved pathway maps20 and the organism-specific pathway maps20, respectively. The colors indicate the category of the pathway maps in the KEGG database (see Table 2). Orange, "carbohydrate"; brown, "energy"; blue, "lipid"; purple, "nucleotide"; red, "amino acid"; magenta, "other amino acids"; sky-blue, "glycan"; green, "cofactors and vitamins" and yellow, "genetic information processing". The notes in the boxes are abbreviations for the pathway maps, using a few words from the long descriptions in Table 2. Note that the amino acids (colored red and magenta) are denoted by three letter codes. A directed edge indicates the flow of one compound. The blue directed edges entering the central cell from the environment indicate the imports of nutrients. The exchanged compounds between pathway maps and the nutrients imported from extracellular environment are listed in Additional file 2: Table S3.