The induction of sporulation in mould fungi

Abstract

Sporulation of Penicillium griseofulvum is rapidly induced in submerged conditions when mycelium is placed in a medium containing a high concentration of glucose but without assimilable nitrogen. External Mg 2+ , K + , and PO3/4~ are required for sporulation. In these conditions the induction of sporulation is completed in 3 to 4 h, before there is any sign of conidiophore formation. The high concentration of glucose required for sporing can be effectively replaced by an equivalent concentration of non-assimilable sugars (sorbose, D-arabinose) provided a small amount of glucose is present to supply the energy requirements of the fungus. High concentrations of salts are not effective and tend to inhibit sporing. Induction of sporing in submerged conditions is inhibited by certain concentrations of ascorbate, Hg 2+ , cetyltrimethylammonium bromide and 3,4-dichlorphenylserine which do not affect vegetative growth. The most powerful stimulus to sporulation in Penicillia and other fungi comes from emergence of mycelium from submerged into aerial conditions. Experiments with P. griseofulvum and P. chrysogenum show that emergence of the mycelium causes a sharp change in physiological behaviour which is manifest before any morphogenetic changes are apparent. Aerial mycelium assimilates NH 4 + in the complete absence of external carbohydrate, whereas submerged mycelium will not assimilate NH^ in these conditions even when fully aerated. The aerial stimulus is not associated with the supply of 0 2 nor with concentration of C0 2 nor with water loss from the mycelium. Evidence from three independent methods of investigation points to the occurrence of an abrupt change in the physical condition of the cell surface when mycelium emerges from a liquid medium into the air. Each method indicates a physical change which takes place within a few seconds of emergence, which increases slowly with time in aerial conditions, and which, like aerial sporulation itself, is reversed or delayed by re-wetting. It is considered that the primary aerial stimulus to sporulation is associated with some physical change at the cell surface caused by the abrupt formation of an air/water interface.

The Production of Sporidesmin and Sporidesmolides by Wild Isolates of Pithomyces chartarum in Surface and in Submerged Culture

“…The differences observed between growth in submerged and in surface culture resemble those described for other organisms (Morton, 1960). Thus in submerged cultures growth was more rapid with a shorter lag period.…”

“…in diameter on the third day of incubation; it is likely that such cultures were not completely ' submerged '. This would account for the appearance of conidia in cultures of isolate S73a (Morton, 1960). The occurrence of this abnormal growth was erratic and sometimes difficult to detect in vessels where very 9-2 heavy growth had occurred.…”

“…It was therefore of interest to determine whether sporidesmin and sporidesmolides were produced by field isolates and also whether such isolates differed in ability to produce these metabolites. It is known (Morton, 1960) that many fungi produce fewer spores in submerged culture than in surface culture. Thus it is possible to compare the same organism growing on the same medium a t the same temperature under conditions where one culture produces many times the number of conidia produced by the other.…”

Signal Transduction Cascades Regulating Fungal Development and Virulence

“…In fact, while sporulation in many microorganisms occurs in response to adverse environmental conditions, the signals that induce A. nidulans differentiation are not well defined. Under normal growth conditions, the only environmental requirement is exposure to air (15,200). This requirement for air does not appear to involve O 2 or CO 2 levels, but rather results from changes in the cell surface induced by the abrupt formation of an air-water interface.…”

Light is required for conidiation in Aspergillus nidulans.

“…The extrinsic environmental conditions required for initiating sporulation in this organism are poorly understood. It has been shown previously that conidiation is strongly inhibited in submerged culture but occurs readily when the mycelia are exposed to an air interface (Morton 1961;Axelrod et al 1973). The physiological basis for this effect does not appear to involve an osmotic change, because conidiation occurs in surface cultures when the atmosphere is saturated with water (Timberlake and Hamer 1986).…”