Temperature induction of bacteriophage λ mutants in Escherichia coli

Abstract

The paper presents temperature induction in Escherichia coli cells with phage λ on the target-protein production and cell growth. Replicated A-DNA particles in the Q − and S − mutants remain naked for a longer time by preventing DNA packaging and cell lysis, and therefore the expression of the foreign genes is high. However, the parasitic infection of phage-A causes on significant losses of host cell viability in the induction phase. The temperature effects on cell growth and targeted-gene product formation were investigated. Gene amplification was found to be growth phase dependent for both Qam73 (Q mutation) and Sam100 (S mutation) mutants. Maximum induction occurs in the early exponential phase and under the optimal cell density. The total β-galactosidase activity at this optimal induction condition increases roughly 8–10-fold with respect to that without thermal induction. To maximize the induction efficiency for the gene-product β-galactosidase activity, several operating parameters were investigated. In this study, temperature induction is strongly dependent upon the population density of ‘susceptible’ cells at which time the temperature is shifted to 38–42 °C. This may be due to the ‘threshold’ population density to regulate the infection of A to hosts and control the productivity of target gene expression.