THE INDUCTION OF LAMBDA PROPHAGES BY CONTROLLED DESICCATION

Abstract

Cells of Escherichia coli K12 (λ +) and Escherichia coli M3 (λ59) were desiccated at various levels of relative humidity (R.H.). When the cells were cultured in an enriched medium and held at 55% R.H., induction of the prophage in 36% of E. coli K12 cells and 75% of E. coli M3 cells occurred. At 30% R.H. or 70% R.H., fewer inductions took place. The maximum number of cells in which prophage induction occurred was found 15 minutes after desiccation began with E. coli K12 and immediately after the cells were dried with E. coli M3. After the attainment of maximum levels of induction, plaque-forming ability was gradually destroyed, but the rate of destruction was dependent on the R.H. at which the cells were held. The plaque-forming ability of the free viruses and of cells in which prophage induction had occurred were destroyed by prolonged desiccation at different rates. Also, the loss of colony-forming ability of the cells was more rapid than the inactivation of plaque-forming ability of either induced prophages or the free viruses. The compound, i-inositol, prevented prophage induction by desiccation and also stopped the destruction of induced prophages within the cell.It is concluded that water molecules bound to the DNA hold the prophage to the host DNA and their removal results in induction.