Autolysis of Penicillium oxalicum with special reference to its cell walls

Abstract

Cultures of Penicillium oxalicum growing on a denned medium supplemented with yeast extract reached the onset of autolysis after 3 days at 25 °C. Thenceforth, autolysis was progressive and eventual reductions in dry weight of 96% were recorded by day 47. The pH of the medium fluctuated between 4.0 during the exponential phase of growth and 9.0 during autolysis. Electron microscopy of autolyzing cultures revealed a progressive loss of cytoplasmic ultrastructure. Digestion of the cell walls, with a rapid hydrolysis of the three external layers and a low hydrolysis of the two inner layers, was accompanied by deep pitting and by loss of the distinct five-layered structure. A lytic enzyme complex was obtained from the filtrates of extensively autolyzed cultures. It was rich in (1 → 3)-β-glucanase and other enzymes active against a range of fungal cell wall and storage polysaccharides. This enzyme complex degraded extensively isolated cell walls of P. oxalicum and three other Ascomycetes but had less effect on walls isolated from Mucor mucedo or Schizophyllum commune. In the case of P. oxalicum, cell walls harvested from young cultures were more readily digested than were the walls from older cultures.