Berk, Richard S. (Wayne State University, Detroit, Mich.). Nutritional studies on the "auto-plaque" phenomenon in Pseudomonas aeruginosa. J. Bacteriol. 86:728-734. 1963.-Examination of 20 cultures of Pseudomonas aeruginosa indicated that 18 cultures possessed the common property of spontaneously lysing to form "plaques" or erosions on themselves in the absence of a sensitive indicator strain. Maximal lysis and plaque production was found to occur on a medium with a Tryptone concentration of 2.0 to 2.5%. Reduction of the Tryptone concentration to 0.5% or less supported growth, but was usually inadequate for support of lysis. However, addition of l-asparagine or l-arginine to 0.5% Tryptone induced lysis. Examination of five strains of Pseudomonas, which routinely exhibited the autolytic phenomenon, indicated that all were both lysogenic and pyocinogenic when tested against other Pseudomonas strains on both 2 and 0.5% Tryptone. Culturing of autolytic strain Pa-1 on a simple medium composed of glucose and inorganic salts appeared to be inadequate for "auto-plaque" formation, although lysis occurred occasionally when a yeast extract concentration of 1% was incorporated into the medium. Suppression of auto-plaque formation was also effected by growing the culture on Technicon dialyzing membrane D3 overlaid on 2% Tryptone, although lysogenic lysis of an indicator strain was demonstrable on the membrane.