TIMING OF LIFE-CYCLE MORPHOGENESIS IN SYNCHRONOUS SAMPLES OF STERKIELLA-HISTRIOMUSCORUM .1. THE VEGETATIVE CELL-CYCLE

We describe standardized growth conditions and protocols for manipulat ing the life cycle of a common stichotrich ciliate, Sterkiella histrio muscorum (Oxytrichidae), previously isolated as Oxytricha fallax. High density cultures were obtained with short cell cycles and with predic table kinetics of growth or differentiation. By manipulating the cultu re conditions eve could obtain mass cultures undergoing conjugation, e xcystment, encystment or cannibalism. Under poor growth conditions, ce lls down-size by rescaling the cytostome and macronuclear DNA content, as do other Oxytrichidae. Using synchronous samples obtained from cul tures in each of the life cycle phases, we describe in detail the timi ng of morphogenesis stages in the vegetative cell cycle, in encysting cells and in excysting cells. The timing of the nuclear and cortical e vents are correlated to obtain a cell cycle diagram. This establishes a firm base for study and manipulation of the life cycle differentiati on and cell cycle regulation of a stichotrich ciliate at the genetic a nd physiological level.