THE INITIATOR CELL FOR SLIME MOLD AGGREGATION

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Abstract
Dictyostelium discoideum Raper, strain NC-4 wild type, was grown on SM agar in association with Aerobacter aerogenes and the myxamoebae were harvested and washed free of occluded bacteria after an appropriate incubation period. I-cells were recognized in the myxamoebae by their larger size, extensive lobose pseudopodia and heavier granulation when compared with the cell type present in majority. Data is presented suggesting that the I-cell is the initiator cell for slime-mold aggregation. I-cells induced aggregates among test populations to which they were added and the proportion of I-cells was about 20% in excess of the number of centers that could be formed at optimal density. A high correlation was encountered between the positions of I-cells and of centers subsequently established. Removal of I-cells at a very early stage destroys the capacity of populations to form aggregates. If any alternative mechanism of center formation operative in slime mold aggregation does exist, it apparently plays an insignificant role under the conditions employed in these experiments.