Autolysis of Penicillium chrysogenum-A Holistic Approach

Abstract

Despite of its biotechnological significance, the autolysis of filamentous fungi is a poorly studied and understood area of fungal physiology. The autolysis of 13-lactam producing fungus, Penicillium chrysogenum shares some similarities with the apoptosis of higher eukaryotes. For example, the biosynthesis and processing of age-related hydrolases were highly regulated in carbon-depleted cultures. The in vivo inhibition of autolytic chitinase activity hindered considerably the disintegration of pelleted structures that are typical of the exponential growth phase. In the absence of conidiation, round-ended yeast-like hyphal fragments were the dominant surviving morphological forms, which were characterised with decreasing total respiration, increasing cyanide-resistant respiration, intracellular accumulation of reactive oxygen species (ROS) and declining viability in the autolytic and post-autolytic phases of growth. The term ageing was used to describe these physiological changes, and the surviving fragments may undergo oxidative-stress induced programmed cell death. Although variations in oxygen tension and extracellular ROS concentrations are key elements in the initiation of morphological changes, the genomic expression programmes of fungi governing morphological transitions including autolysis are likely to be activated by different kinds of environmental stress and signal transduction pathways. The glutathione (GSH) and ROS metabolisms of P. chrysogenum were influenced by many extrinsic and intrinsic factors in each growth phase studied. As a consequence, no firm correlation was found between the GSHIglutathione disulphide (GSSG) redox status, the intracellular ROS levels and the observed morphological and physiological characteristics of the cells.