Environmentally compatible synthesis of adipic acid from d -glucose.
This work demonstrates the feasibility of applying metabolic engineering for generating E. coli strains for the production of catechol from glucose via anthranilate. These results are a starting point to further optimize environmentally-compatible production capacity for catechol and derived compounds.
Environmentally compatible synthesis of ..
Important differences exist concerning strain characteristics and catechol production efficiency when comparing synthesis routes starting from either DHS or anthranilate. When considering the catechol synthesis route starting from DHS, the maximum theoretical yield from glucose is 0.686 gCat/gGlc, Five enzyme catalyzed steps are required to transform DHS to anthranilate. In one of these steps, PEP is consumed for the synthesis of intermediate 5-enolpyruvylshikimate-3-phosphate. Considering this extra carbon atoms requirement, the maximum theoretical yield from glucose for catechol synthesis from anthranilate corresponds to 0.376 gCat/gGlc. On the other hand, the inactivation of gene aroE encoding SHIK dehydrogenase to cause DHS accumulation results in a deficiency to synthesize the aromatic amino acids and vitamins . This multiple auxotrophy is a potential problem when employing a minimal medium in a production process. However, this deficiency can be circumvented by supplementing the culture medium with the required aromatic compounds or the intermediate shikimate. In contrast, inactivation of trpD causes a tryptophan auxotrophy, therefore, this amino acid must be supplemented when culturing in minimal medium. Considering these important differences, it remains to be determined which of the two catechol-production routes, based on DHS or anthranilate as starting precursors, is more cost-effective under industrial production conditions.
Catechols are important intermediates for the synthesis of pharmaceuticals, agrochemicals, flavors, polymerization inhibitors, and antioxidants (, ). Currently, catechol is produced primarily by the oxidation of phenol and m-diisopropylbenzene or by coal-tar distillation (). However, the industrial routes to catechols, e.g., the use of elevated metal, temperature, pressure, and solvent conditions, are environmentally unsafe (, ). These chemical routes are often lengthy, energy-intensive, multistep reactions that require expensive starting materials and are plagued with isomerization and rearrangement problems (, ); hence, microbial production of catechols is attractive. Previously, catechol has been produced by transforming -glucose with a genetically modified Escherichia coli AB2834/pKD136/pKD9.069A strain expressing 3-dehydroshikimic acid dehydratase and protocatechuic acid decarboxylase (, ) and by benzene oxidation with Pseudomonas putida 6-12 expressing toluene/benzene dioxygenase while lacking catechol 1,2-oxygenase and catechol 2,3-oxygenase ().