Influence of increased aspartate availability on lysine formation by a recombinant strain of Corynebacterium glutamicum and utilization of fumarate

Aspartate availability was increased in Corynebacterium glutamicum strains to assess its influence on lysine production. Upon addition of fumarate to a strain with a feedback-resistant aspartate kinase, the lysine yield increased from 20 to 30 mM. This increase was accompanied by the excretion of malate and succinate. In this strain, fumaric acid was converted to aspartate by fumarate hydratase, malate dehydrogenase, and aspartate amino transferase activity. To achieve the direct conversion of fumarate to aspartate, shuttle vectors containing the aspA+ (aspartase) gene of Escherichia coli were constructed. These constructions were introduced into C. glutamicum, which was originally devoid of the enzyme aspartase. This resulted in an aspartase activity of 0.3 U/mg (70% of the aspartase activity in E. coli) with plasmid pZ1-9 and an activity of up to 1.05 U/mg with plasmid pCE1 delta. In aspA+-expressing strains, lysine excretion was further increased by 20%. Additionally, in strains harboring pCE1 delta, up to 27 mM aspartate was excreted. This indicates that undetermined limitations in the sequence of reactions from aspartate to lysine exist in C. glutamicum.