Production of L ‐DOPA and dopamine in recombinant bacteria bearing the Vitreoscilla hemoglobin gene

Given the well‐established beneficial effects of Vitreoscilla hemoglobin (VHb) on heterologous organisms, the potential of this protein for the production of L ‐DOPA and dopamine in two bacteria, Citrobacter freundii and Erwinia herbicola , was investigated. The constructed recombinants bearing the VHb gene ( vgb + ) had substantially higher levels of cytoplasmic L ‐DOPA (112 mg/L for C. freundii and 97 mg/L for E. herbicola ) than their respective hosts (30.4 and 33.8 mg/L) and the vgb – control strains (35.6 and 35.8 mg/L). Further, the vgb + recombinants of C. freundii and E. herbicola had 20‐fold and about two orders of magnitude higher dopamine levels than their hosts, repectively. The activity of tyrosine phenol‐lyase, the enzyme converting L ‐tyrosine to L ‐DOPA, was well‐correlated to cytoplasmic L ‐DOPA levels. As cultures aged, higher tyrosine phenol‐lyase activity of the vgb + strains was more apparent.