THE INFLUENCE OF LIGHT ON THE TIME OF CELL AGGREGATION IN THE DICTYOSTELIACEAE

¹ Departments of Bacteriology and Botany, University of Wisconsin, Madison 6, Wisconsin

The time at which aggregation begins in the Dictyosteliaceae was found to be influenced by the conditions of light to which the myxamoebae were exposed during the vegetative and preaggregative stages. The myxamoebae were usually pregrown in the dark on Escherichia coli or Aerobacter aerogenes, harvested, washed by centrifugation, resuspended, deposited on non-nutrient agar, and incubated under varying regimens of light and darkness. Myxamoebae of the single strains of Dictyostelium mucoroides, D. purpureum, Polysphondylium violaceum and P. pallidum included in the tests, and one strain of D. discoideum (Acr-12), aggregated earliest if exposed to constant light. Other strains of D. discoideum, including the type, NC-4, and substrains derived from it, aggregated optimally after an initial dark period of 6 to 8 hours followed by about 4 hours of light. When these latter strains were grown in light rather than in darkness, the initial dark period required for early aggregation was reduced to 4 hours. When light-grown cells of strain NC-4(H) were mixed with cells grown in the dark, the time of aggregation of the latter was accelerated, but the addition of such cells did not induce dark-grown cells to aggregate as quickly as populations of light-grown cells alone.