Application of l-glutamate oxidase from Streptomyces sp. X119-6 with catalase (KatE) to whole-cell systems for glutaric acid production in Escherichia coli

Whole-cell systems offer many benefits for biochemical production, such as relatively easy enzyme control and higher tolerance toward harsh environments, than purified enzymes. These systems can be applied to many bioconversion reactions, but they sometimes require cofactor regeneration units to support reactions at high substrate concentrations. Here, we examined l-glutamate oxidase (GOX) from Streptomyces sp. X119-6, which produces α-ketoglutarate (α-KG) from l-glutamate, and catalase (KatE) from Escherichia coli, which removes hydrogen peroxide generated by GOX. After optimizing the expression vector, pH, strains, culture conditions, and isopropyl β-d-1-thiogalactopyranoside concentration, we compared their efficiency to that of a previously reported GOX from Streptomyces mobaraensis. Our results indicated that GOX from Streptomyces sp. X119-6 and KatE increased α-KG production by 2.76-fold. This GOX required high levels of α-KG as an amino donor to convert 5-aminovaleric acid to glutaric acid. Performing the reaction at pH 8 enabled us to avoid the exogenous addition of catalase, but severe substrate inhibition was observed, resulting in the production of 287 mM glutaric acid. This α-KG regeneration system has potential for improving production in various aminotransferase systems.