Timing of life cycle morphogenesis in synchronous samples of Sterkiella histriomuscorum I. The vegetative cell cycle

Abstract

Summary We describe standardized growth conditions and protocols for manipulating the life cycle of a common stichotrich ciliate, Sterkiella histriomuscorum (Oxytrichidae), previously isolated as Oxytricha fallax . High density cultures were obtained with short cell cycles and with predictable kinetics of growth or differentiation. By manipulating the culture conditions we could obtain mass cultures undergoing conjugation, excystment, encystment or cannibalism. Under poor growth conditions, cells down-size by rescaling the cytostome and macronuclear DNA content, as do other Oxytrichidae. Using synchronous samples obtained from cultures in each of the life cycle phases, we describe in detail the timing of morphogenesis stages in the vegetative cell cycle, in encysting cells and in excysting cells. The timing of the nuclear and cortical events are correlated to obtain a cell cycle diagram. This establishes a firm base for study and manipulation of the life cycle differentiation and cell cycle regulation of a stichotrich ciliate at the genetic and physiological level.