This study examined how prophage integration affects the efficiency of plating (e.o.p.) in Escherichia coli K12 strains. Researchers measured viable cell counts during the transition from lag to exponential growth phase in cultures grown at various temperatures (30-42°C). The non-lysogenic K12 C600 strain and the lambda-lysogenic K12 C600(λ) strain both showed significantly reduced viable cell counts during this growth transition. However, when K12 C600 was lysogenized with a non-inducible mutant prophage (λind), the reduced e.o.p. phenomenon was suppressed, and the growth pattern resembled the control strain B. The reduction in viable cells was transitory and temperature-independent. The findings indicate that the prophage itself is not responsible for the decreased e.o.p., but rather the quality of the repressor protein produced by the prophage. The non-inducible λind mutant produces altered repressor molecules insensitive to ultraviolet or X-ray induction, suggesting that repressor synthesis and molecular quality influence host cell physiology during the growth transition phase.

Key findings

• Lysogenic E. coli K12 strains carrying wild-type λ prophage showed decreased efficiency of plating during transition from lag to exponential growth phase, while non-lysogenic K12 C600 exhibited the same phenomenon
• The decreased e.o.p. was suppressed in K12 C600(λind) lysogen carrying a non-inducible prophage mutant, indicating the defect is not inherent to lysogeny
• The quality and function of prophage repressor protein, not merely prophage presence, influences host cell physiology and viability during growth phase transitions
• The phenomenon was temperature-independent (30-42°C) and transitory in nature