E. coli aroD mutants have defects in shikimate biosynthesis and fail to produce diverse aromatic metabolites. An abbreviated sequence of reactions involved in the E. coli biosynthesis of shikimate (SHK) and chorismate, and the products of this metabolism, are indicated. Black solid arrows indicate one step; black dashed arrows indicate multi-step pathways (four gene products catalyzing three steps convert SHK to chorismate). Chorismate is a precursor in the synthesis of aromatic amino acids (Phe, Tyr, Trp), menaquinol (used in E. coli respiratory electron transport and a precursor of vitamin K), enterobactin (a siderophore used by E. coli to acquire iron), 4-hydroxybenzoic acid (4-HB; a precursor of coenzyme Q) and para-aminobenzoic acid (pABA; a precursor of folate). Addition of either SHK or pABA reversed the lifespan extension in C. elegans fed a diet of aroD mutant E. coli (green boxes). In contrast, addition of the aromatic amino acids or 4-HB failed to reverse the lifespan extension (red dashed boxes). pABA also serves as a precursor of coenzyme Q in the yeast Saccharomyces cerevisiae . However, it is not yet know whether pABA is an aromatic ring precursor in coenzyme Q biosynthesis in E. coli (red dashed arrow with question marks). Sulfa drugs mimic pABA and hence inhibit folate biosynthesis in microbes, but the effect on coenzyme Q has yet to be determined.