Morphological synchrony in axenic cultures of Chytridium confervae, a promising developmental system

Abstract

Nonfilamentous, lower, aquatic fungi are potential systems for developmental study. Chytridium confervae , a monocentric, eucarpic chytrid, exemplifies the morphological and developmental simplicity of these fungi. It is easily isolated and maintained in axenic culture, and will grow and reproduce asexually in liquid culture under a variety of conditions. The degree of synchrony of growth, differentiation, and zoospore release of large populations of cells of C. confervae in axenic liquid cultures is directly related to culturing conditions. Under a specific set of conditions, called standard conditions, large populations of cells undergo rapid and consistent exponential growth as measured by increases in cell diameter. If cells are induced to sporulate just prior to the end of the exponential growth phase, a sequence of morphological events associated with zoosporangial differentiation and zoospore release occurs in a predictable pattern and with a high degree of synchrony. Between 2.5 and 4.0 h after induction, a period of time that constitutes 5% of the asexual generation time, over 95% of the cells develop opercula. During this same period, a relatively high percentage of cells undergoes mitosis. Between 6 and 7 h after induction, whole populations of cells release zoospores. The synchronization index is over 0.90 in both petri dish cultures and spinner flask cultures under standard conditions. This degree of synchrony is comparable to that reported in cultures of Blastocladiella emersonii . A variety of midicycles are possible with C. confervae and it can be grown on a defined medium, Crasemann's 1B. The high degree of synchrony and control of large populations of C. confervae in axenic culture makes it adaptable to morphological and molecular studies of development.