Iron-induced pigment formation and ionizing radiation resistance in three strains of Micrococcus violagabriellae

Three strains of Micrococcus violagabriellae-Littlepig, Pig (Parental), and Superpig--were studied. The pulcherrimin pigment (which imparts a violet-red color to the colonies of the Parental and Superpig strains) is produced only when the cells are grown in the presence of excess iron and provides a unique system for the study of the radioprotection conferred by a pigment. Cell suspensions of each of the three strains (initially grown in the presence and in the absence of excess iron) were exposed to gamma rays and plated on media containing an excess of iron and on media without iron. The survival curves of the treated strains indicate a correlation between the color intensity of the pigment (pulcherrimin), and the ability of the organisms to survive moderate doses of ionizing radiation. Studies using radioactive iron (59Fe) showed that a correlation also exists between the intensity of the pigment and the amount of iron that the cells of each strain can remove from the medium. The effect of gamma irradiation on postirradiation cell growth is discussed for each strain irradiated during logarithmic growth and during a stationary state.