Absence of the Glucose Effect on the Frequency of Lysogenization in Salmonella typhimurium

WHEN a sensitive bacterial cell is exposed to a temperate bacteriophage it may undergo lysis, become lysogenized, or remain uninfected. The relative frequency with which these responses occur depends on the genetic structure of the phage and the conditions of the infection. The outcome may be influenced by temperature1, multiplicity of infection2, and the addition of various chemicals3,4. In a recent paper5, it was reported that glucose added to a nutrient agar medium affected a 100 per cent lysogenic response with Salmonella typhimurium strain LT2 (C+dgs)6and phage PLT22, while a glucose diauxie-resistant variant of this strain (C+dgr−1)6was found to be immune to this apparent glucose effect. These conclusions were based on observations of ‘turbid’ or ‘less turbid’ plaques as the criteria for lysogenization or lysis, respectively, of the initially infected cell. Recent attempts to duplicate these experiments were not successful, nor could any glucose effect on the frequency of lysogenization be detected using a more direct and reliable method developed by Luria and Fraser (ref. 4). (We wish to thank E. Bertani for details of the method and the indicator strain.)