Optimization of bacteriophage λ Q^--containing recombinant Escherichia coli fermentation process

Q^- mutant phage λ is deficient in the synthesis of the proteins involved in cell lysis and λ DNA packaging. As a result, the replicated Q^- λ DNA containing a cloned gene is not easily coated by a phage head and remains naked for the ample expression of the cloned gene, and also the host cells do not lyse easily and larger amounts of cloned gene products are produced. In a two-phase operation, the first phase is operated at a low temperature to keep the phage in the lysogenic state for cell growth and cloned gene stability, while the second phase is operated at a high temperature to induce the lytic state for the amplification of the cloned gene and overproduction of its product. This two-phase operation was optimized by determining both the optimal temperatures for the growth and production phases and the optimal switching time between the growth to the production phase. The optimal temperatures for growth and production phases were 33 and 40 °C, respectively. The optimal switching time was 3 h. The recombinant β-galactosidase production using this optimal process was about 20 times higher than in the single-copy lysogenic state.