Continuous production of L-tryptophan from indole and L-serine by immobilized Escherichia coli cells

Escherichia coli B 10, which has high activity of tryptophan synthetase, was grown in a 50‐L batch culture in order to determine in which growth phase the cells have the highest specific tryptophan productivity. Accordingly, whole cells of the stationary phase were used for immobilization in polyacrylamide beads. After immobilization, these immobilized cells had 56% activity of tryptophan synthetase compared with that of free cells. First, the properties of immobilized cells were investigated. Next, discontinuous productions of L‐tryptophan were carried out by using immobilized cells. In discontinuous production of L‐tryptophan by the batch, the activity remaining of immobilized cells was 76–79% after 30 times batchwise use. In continuous production of L‐tryptophan with a continuous stirred tank reactor (CSTR), the activity remaining of the immobilized cells was 80% after continuous use for 50 days. The maximum productivity of L‐tryptophan in this CSTR system was 0.12 g tryptophan L−1 h−1.