The effects of elevated temperatures on spore swelling and germination in Aspergillus niger

Abstract

Exogenous carbon and nitrogen sources were necessary for complete swelling (spherical growth) and germ-tube formation from Aspergillus niger spores. The rate of spherical growth was low at 30°, maximum at 38°, and decreased at higher temperatures until at 47° inhibition was complete. At temperatures from 35° to 44° the final spore size was similar and greater than at 30° although the time taken to reach this size varied. Germ-tube formation occurred in from 97 to 99% of the spores with a good degree of synchrony between 30° and 38°. At temperatures from 38° to 43° the proportion of spores which produced germ tubes gradually decreased with a concurrent loss of synchrony. At 44° germ-tube formation was completely inhibited although spherical growth could occur over a prolonged period to produce large spherical cells. This increase of cell volume was apparently accompanied by a system of wall extension which involved wall synthesis. Under conditions of spore crowding an inhibition became apparent which affected only the initiation of spherical growth and not the spherical-growth process itself. Other effects of spore crowding were observed and were attributed to alterations in the gaseous environment. Increased spherical growth was always accompanied by a greater degree of branching of the germ tube when produced and a hypothesis relating these effects is suggested.