Encystment of Chattonella antiqua in laboratory cultures

Cysts of Chattonella antiqua (Raphidophyceae) were obtained in laboratory cultures for the first time. They were formed on the surface of glass coverslips added to both P- and N- depleted mediums. The yield was 50-250 cysts/cm super(2). Crossing experiments showed the highest cyst production in mixed cultures, although cysts were observed in clonal cultures as well. Cysts had approximately double the DNA content of synchronously growing vegetative cells (G sub(1) phase). The encystment process was also monitored: Under P-depleted conditions, "small cells" were formed that fused to become a "triangle"-shaped cell which in turn changed into a cyst. These results strongly suggest that cysts are the products of fusion and are diploid. "Small cells", "triangle"-shaped cells, and cysts are considered to be gametes, planozygotes, and hypnozygotes, respectively. Significant mortality was observed in laboratory cysts stored in the cold and dark for five months, although those remaining were capable of germination to reestablish a motile, vegetative population.