MEASUREMENT OF AUTOLYSIS IN SUBMERGED BATCH CULTURES OF PENICILLIUM-CHRYSOGENUM

The process of cellular autolysis was studied in an industrial strain of Penicillium chrysogenum by a range of methods, including assessment of biomass decline, NH4+ release, changes in culture apparent viscosi ty, and by means of a quantitative assessment of changes in micromorph ology using a computerized image analysis system. The pattern of total intracellular proteolytic and beta-1,3-glucanolytic activity in the c ulture was also examined. The overall aim was to identify a suitable m ethod, or methods, for examining the extent of autolysis in fungal cul tures. Autolysis was studied in submerged batch processes, where DOT w as maintained above 40% saturation (non-O-2-limited), and, under O-2-l imited conditions. Both N and O-2 limitation promoted extensive cultur e autolysis. Image analysis techniques were perhaps the most sensitive method of assessing the progress of autolysis in the culture. Autolyt ic regions within some hyphae were apparent even during growth phase, but became much more widespread as the process proceeded. The early st ages of autolysis involved continued energy source consumption, increa sed carbon dioxide evolution rate, degradation of penicillin, and decr eased broth filterability. Later stages involved widespread mycelial f ragmentation, with some regrowth (cryptic growth) occurring in non-O-2 -limited cultures. Intracellular tar proteolytic activity showed two p eaks, one during the growth phase, and the other during autolysis. Aut olysis was also associated with a distinct peak in beta-1,3-glucanolyt ic activity, indicating that degradation of cell wall matrix polymers may be occurring during autolysis in this strain of P. chrysogenum. (C ) 1998 John Wiley & Sons, Inc.