Conyersion of Somatic ‘antigens in Salmonella

The conversion of Salmonella anatultr (group Et, somatic antigens 3, 10) to group I& (antigens 3, 15) by infection with phage cl5 and its virulent mutant P vir has been analyzed. Antigen 15 appears in the cells within a few minutes after infection with either phage. The receptors for another phage, ear, which can be adsorbed only by cells with antigen 15, appear with the new antigen. The receptors for phage CM, which is adsorbed only by cells with antigen 10, disappear following infection. In the early stages the cells have both antigens 10 and 15 and both sets of phage receptors. The cells that SUFvive infection segregate lysogenic and nonlysogenic cells in their progeny. In the nonlysogenic segregants the changes in antigenic structure and in phage receptors initiated by phage infection persist for several generations; later, the cells revert to the typical Ei condition. The results indicate that the converted characters are controlled by vegetative phage as well as by prophage. Their bearing on the mechanism of conversion is discussed.