Synthesis of dopamine in E. coli using plasmid-based expression system and its marked effect on host growth profiles

L-Dopa and dopamine are important pathway intermediates toward the synthesis of catecholamine such as epinephrine and norepinephrine from amino acid L-tyrosine. Dopamine, secreted from dopaminergic nerve cells, serves as an important neurotransmitter. We report the synthesis of dopamine by extending the aromatic amino acid pathway of Escherichia coli DH5α by the expression of 4-hydroxyphenylacetate-3-hydrolase (HpaBC) from E. coli and an engineered dopa decarboxylase (DDC) from pig kidney cell. The activity of HpaBC and DDC require 200 µM iron supplementation and 50 µM vitamin B6, respectively as additives to the growth media. The maximum concentration of L-dopa and dopamine obtained from the broth was around 26 and 27 mg/L after 24 hr of separate shake flask studies. We observed that in the presence of dopamine synthesized in vivo host growth was remarkably enhanced. These observations lead us to an interesting finding about the role of these catecholamines on bacterial growth. It is clear that synthesis of dopamine in vivo actually promotes growth much efficiently as compared to when dopamine is added to the system from outside. From HPLC and GC–MS data it was further observed that L-dopa was stable within the observable time of experiments whereas dopamine actually was subjected to degradation via oxidation and host consumption.