IMMOBILIZED AND FREE-CELL CONTINUOUS CULTURES OF A RECOMBINANT ESCHERICHIA-COLI PRODUCING CATECHOL 2,3-DIOXYGENASE IN A 2-STAGE CHEMOSTAT - IMPROVEMENT OF PLASMID STABILITY

The immobilization of recombinant strains of E. coli W3110/pTG205 in K-carrageenan gel beads improves the plasmid stability during continuous cultures in the absence of selection pressure. Since, xyl E gene (which encodes catechol 2,3-dioxygenase from Pseudomonas putida) transcription is controlled by the trp promoter, the effects of tryptophan (repressor) and 3 β-indolyl acrylic acid (derepressor) on pTG 205 stability and enzyme production have been studied in both free and immobilized cell cultures. A two-stage continuous culture system running for 150 h is described. In the first stage an immobilized culture is performed in the presence of tryptophan with a significant plasmid stability. The cells released from the gel beads are continuously transferred in the second stage reactor where expression is induced by 3 β-indolyl acrylic acid. In these conditions an efficient production of catechol 2,3-dioxygenase is observed. © 1990.