Lysis of Escherichia coli after infection with phiX174 depends on the regulation of the cellular autolytic system.

The relationship between the rate of lysis of Escherichia coli infected with bacteriophage phiX174 and the physiological state of the host bacteria was determined. The lysis rate was comparable to the growth rate only in cells grown in rich media, whereas in minimal medium it was much slower than the growth rate. Lysis of starved cells grown in minimal medium could not be induced by phiX174 although progeny phages were produced. Lysis of E. coli provoked by expression of the cloned phiX174 lysis gene could be prevented by MgSO4 concentrations which also prevented lysis by induced autolysins whereas prevention of lysis of phage-infected E. coli needed much higher concentrations of MgSO4. Prevention of lysis in the latter case did not reestablish viability of the infected cells whereas induction of the cloned phiX174 lysis gene allowed continued multiplication in the presence of MgSO4. Lysis of E. coli by expression of the cloned phiX174 lysis gene was suppressed at pH 6.0 and could be turned on immediately upon upshift to pH 6.8. Phage-infected cells lysed at pH 6.0. At pH 8.0, lysis of E. coli by phage infection or by the cloned lysis gene product was suppressed. pH downshifts in both cases were not followed by lysis. The results suggest that the phiX174 lysis gene product interacts in a reversible manner with the regulation of the autolytic system of E. coli.