| Abstract: | No fruiting of the NC-18 isolate of Acrasis rosea occurs in cultures maintained in continuous light or in continuous dark. The use of different food organisms does not alter the aforementioned behavior. The time at which fruiting occurs in this isolate can be regulated by administering stimulatory light followed by a dark period. Mature sorocarps are formed approximately 14 hr after the termination of light and the start of darkness. Within this 14-hr interval aggregation and sorocarp development occur. After about 6 hr of dark incubation, NC-18 amebae, previously stimulated by light, form a few weak aggregation centers. After 8 hr of dark incubation there are numerous aggregation areas, large in size and deep rose in color. By 10 hr the aggregations are quite compact and firm in appearance, and between 12 and 14 hr late aggregations, sorogens and, finally, mature sorocarps are formed. The minimum dark period, i.e., the minimum time that is required in darkness (for cultures previously stimulated with light) to obtain at least some fruiting within the 14-hr developmental period, is 7–8 hr for NC-18 and 5–6 hr for Tu-26. Maximum numbers of sorocarps form when cultures are given 10–11 hr of uninterrupted dark. Light-stimulated cultures of NC-18 placed in darkness and interrupted by a 10- or 30-min exposure to wide-spectrum blue or cool white fluorescent light an hour prior to the minimal dark period exhibit a 4–5 hr-delay in fruiting when returned to darkness and inspected at intervals following the second irradiation. Growth and fruiting of NC-18 occurred with purified food sources of each of five different species of Chlorella and with the alga Stichococcus bacillaris. This is apparently the first report of the utilization of algae as food sources by a cellular slime mold. Fruiting of NC-18 was readily arrested by lowering the relative humidity to 40–45%. This change in the moisture content of the surrounding air induced microcyst formation. Growth on buffered medium occurred in the entire pH range tested, 3.5–7.6, but fruiting occurred only between pH 5.0 and 6.6. |
