THE INFLUENCE OF LIGHT ON CELL AGGREGATION IN POLYSPHONDYLIUM PALLIDUM

¹ Department of Bacteriology, University of Wisconsin, Madison 6, Wisconsin

Experiments have been performed on the effect of light on cell aggregation and aggregation density in Polysphondylium pallidum, strain WS-320. The results of these experiments may be summarized as follows:

1 . Cell aggregation occurs more quickly and with a greater density of aggregation centers in cultures incubated in the light than in comparable cultures incubated in the dark.

2. Myxamoebae grown in the dark in liquid culture and deposited on agar are most sensitive to light within the first few hours of incubation.

3. Beyond the initial period of sensitivity, there is a diminution in response resulting in an almost complete absence of light-induced aggregation.

4. Little variation in response occurred when myxamoebae were exposed to light for periods of from one to 15 minutes, indicating a fairly sensitive light response mechanism.

5. In cultures grown in situ, exposure to the light following dark incubation induces aggregation in two- to three-day-old myxamoebae. Older myxamoebae fail to display any sign of morphogenetic activity in response to light; they do respond, however, in the presence of charcoal.

6. Of certain physical and chemical agents tested for their effect on aggregation, charcoal and mineral oil were found to increase aggregation density in both light and dark, while CO₂, in the light, had the opposite effect.

The similarity in response achieved by charcoal and mineral oil, and by light, suggests that the action of light may be to change the relationship between aggregation and a center-suppressing factor that accumulates in the environment. In the light, aggregation occurs possibly because light limits the production of or destroys the center-suppressing factor, or renders the cells less sensitive to it. In the absence of light, aggregation may be inhibited by this substance while the cells are shunted in the direction of microcyst formation. If, in the latter situation, charcoal or mineral oil were added prior to actual cyst formation, the suppressor would be absorbed and aggregation could occur.