Whole cell immobilization of recombinant E. coli cells by calcium alginate beads; evaluation of plasmid stability and production of extracellular L-asparaginase

L-asparaginase from Escherichia coli is an important therapeutic agent in the treatment of childhood acute lymphoblastic leukemia. In this study, the secretory production of a recombinant form of L-asparaginase enzyme was investigated in E. coli cells immobilized in calcium alginate beads. The protein expression was determined for the immobilized cells with two different initial cell concentrations and compared with the free cells. The maximum enzyme activity of the released asparaginase was achieved in the culture medium of the alginate beads with the lower cell density at 3 days after immobilization. Total asparaginase activity of the enzymes released into the culture medium or entrapped in the alginate beads was 315.8 U, which exhibited about 2-fold higher activity than the extracellular asparaginase activity of the conventional free cells (162.3 U). A maximum plasmid stability of 49%, which was 25-fold higher than the free cells, was obtained by the immobilized cells.