Role of proteases in autolysis of Penicillium chrysogenum chemostat cultures in response to nutrient depletion

An industrial strain of Penicillium chrysogenum was subjected to carbon or nitrogen limitation in a chemostat and the response monitored in terms of the classical indicators of autolysis (biomass decline and ammonia release), culture degradation (as measured by image analysis) and by obtaining profiles for three classes of proteases implicated in autolysis. Under both sets of conditions (carbon or nitrogen limitation), once started, autolysis involved a succession of different protease activities. The first stages of the process of autolysis in starved chemostat cultures was associated with peaks in the activities of both serine and aspartyl proteases, coinciding with the mobilisation of endogenous energy reserves. Conversely, a peak in the activity of metalloproteases was associated with the later stages of autolysis, perhaps occurring in response to depletion of endogenous energy reserves; the activity of these enzymes led to gross culture degradation, disintegration of ordered mycelial structures and signalled the end of metabolic activity (respiration) within the culture. These findings indicate that strategies intended to control/regulate autolysis in large-scale industrial fungal cultures might profitably be focused on regulation of the activity of key classes of proteases involved in the series of events leading to culture degradation.