Microcycle conidiation in submerged cultures of Penicillium cyclopium attained without temperature changes.

Microcycle conidiation in shaken cultures of Penicillium cyclopium M 79 was induced at 24 degrees C without any shock treatment. The occurrence of a microcycle depended on the presence of an organic acid (especially glutamic acid) in combination with glucose, low phosphate concentration, light and sufficient aeration. Absence of glucose and/or lowered aeration evoked vegetative growth. A synchronous and homogeneous microcycle required a certain relationship between the number of inoculated conidia and the concentration of the organic acid in the medium; the optimum was at 0.08 nmol acid per conidium. Higher values stimulated normal vegetative growth. A shortage or absence of the organic acid led to an atypical growth. The effect of organic acid can be partially replaced by addition of 2% (w/v) CaCO3. Addition of NH+4 in concentrations higher than 6 mM to cultures with glutamate or glutamine evoked vegetative growth.