Inactivation of Intracellular Phage Precursor by Iodoacetic Acid. ∗

There exists experimental evidence for the view that phage production involves the reaction: Inactive intracellular phage precursor+ phage→ phage. 1 The phage precursor has been shown to develop whenever the environmental conditions favor active bacterial metabolism and growth. 2 We term cells which contain a store of precursor “activated bacteria”, and have found that the precursor content of the bacteria is very thermolabile, being destroyed at rapid rates when the cells are heated to 45°-5O°C. 3 At these temperatures destruction of the precursor takes place long before sufficient damage is done to the cells to destroy their reproductive mechanism. The critical thermal increment for heat inactivation is 90,000, suggesting that the precursor either is a protein or contains a protein.

In the present paper we wish to report experiments in which destruction of precursor was brought about by concentrations of iodoacetic acid that were not lethal for the bacteria used.

Activated staphylococci were prepared by growing the organisms in a heavily oxygenated medium. 2 The activated cells were separated from the broth, resuspended in phosphate buffer solution of pH 6.1 and were stored for 1 hour at 5°C before using. Four ml aliquots of activated cell suspension were added to 1 ml amounts of varying concentrations of iodoacetic acid. The mixtures were kept at 5°C for given periods of time after which aliquots were tested for the presence of phage precursor and for the numbers of viable bacteria per ml. The precursor test was done by adding 4 ml amounts of cell suspension to 1 ml of phage solution containing 1 × 10⁹ activity units/ml. 4 The test suspensions were kept at 5°C for 6 minutes to allow interaction of phage and residual activated cells after which they were diluted for titration.