Optimum melanin production using recombinant Escherichia coli

Aims: A parametric study was conducted to define optimum conditions to achieve high yields in the conversion of tyrosine to eumelanin (EuMel) using recombinant Escherichia coli. Methods and Results: Escherichia coli W3110 (pTrcMutmelA) expressing the tyrosinase coding gene from Rhizobium etli and glucose‐mineral media were used to transform tyrosine into EuMel. Batch aerobic fermentor cultures were performed to study the effect of temperature, pH and inducer concentration (isopropyl‐d‐thio‐galactopyranoside) on melanin production. Under optimum conditions, 0·1 mmol l−1 of isopropyl‐d‐thio‐galactopyranoside, temperature of 30°C, and changing pH from 7·0 to 7·5 during the production phase, a 100% conversion of tyrosine into EuMel is obtained. Furthermore, tyrosine feeding allowed us to obtain the highest level (6 g l−1) of EuMel produced by recombinant E. coli reported until now. Conclusions: The most important factors affecting melanin formation and hence influencing the rate and efficiency in the conversion of tyrosine into EuMel in this system, are the temperature and pH. Significance and Impact of the Study: Maximum theoretical yield was obtained using a simple culture process and mineral media to convert tyrosine (a medium value compound) into melanin, a high value compound. The process reported here avoids the use of purified tyrosinase, expensive chemical methods or the cumbersome extraction of this polymer from animal or plant tissues.