In times of iron deficiency, iron uptake is controlled by three genes: "ent", "fep", and "fes" for synthesis, export, and uptake of ferric Enterobactin and its hydrolytic cleavage to release Fe3+ into the cell. This production of this compound is controlled by eight genes: entA-entF, entH, and entS. In E. coli, all of these genes are controlled by the Fur repressor, such that the genes are turned on when the concentration of iron in the environment is low. From these six genes, EntA, EntB, and EntC are responsible for the synthesis of DHB from chorismic acid and the gene EntA encodes the information of 2,3-diDHB dehydrogenase. Without , , and , the bacteria show almost an absolute requirement of DHB in order to survive. Production of siderophores also exhibited in some plant-infecting bacteria, such as "Agrobacterium tumefaciens". The enzyme is controlled by gene cluster agb and the production of 2,3-diDHB dehydrogenase is controlled by the gene agbA. The enzyme AgbA is homologous to the EntA enzyme in "E. coli", the same enzyme that produces 2,3-diDHB dehydrogenase.