Process optimization using single-factor experiments and Taguchi methodology for biotransformation L-Tyrosine into L-DOPA by a novel bacterium Paenibacillus sp. strain CT4W

Since the introduction of L-dopa (3, 4-dihydroxylphenyl-L-alanine) in the 1960s, L-dopa has been recognized as a gold-standard medical therapy for Parkinson’s disease. In the present work, a newly tyrosine-transforming strain of Paenibacillus sp. CT4W was used for the biotransformation of L-tyrosine to L-DOPA. The process parameters were optimized using single- factor experiments and Taguchi design methodology under resting cell strategy. Based on the values obtained in single-factor experiments, the optimum parameters for L- DOPA production: cell mass 6g/l, Cu+2 0.045 g/l, Temperature 30º C, pH 7, agitation 150 rpm and 0.5 g/l of yeast extract as cosubstrate. The maximum yield achieved with these parameters was 0.29 g/l after 16 h incubation. A Taguchi L16 orthogonal array was subsequently employed for further optimization. The biotransformation reaction having 5 g/l cell mass, 1.5 g/l tyrosine and 0.03 g/l Cu+2 was found to be optimum for maximum L-DOPA production. Under the optimized conditions, resting cells of Paenibacillus sp. CT4W produced 0.96 g/l L-DOPA, with a molar yield of 53.5 % after 20 h incubation.