Role of hydrolytic enzymes and oxidative stress in autolysis and morphology of Blakeslea trispora during β-carotene production in submerged fermentation

Abstract

The role of hydrolytic enzymes (proteases and chitinase) and oxidative stress in the autolysis and morphology of Blakeslea trispora during beta-carotene production from a chemically defined medium in shake flask culture was investigated. The process of cellular autolysis was studied by measuring the changes in biomass dry weight, pH, concentration of beta-carotene, specific activity of the hydrolytic enzymes and micromorphology of the fungus using a computerized image analysis system. In addition, the phenomenon of autolysis was associated with high concentrations of reactive oxygen species (ROS). The accumulation of ROS produced during fermentation causes oxidative stress in B. trispora. Oxidative stress was examined in terms of the activities of two key defensive enzymes: catalase (CAT) and superoxide dismutase (SOD). The profile of the specific activities of the above enzymes appeared to correlate with the oxidative stress of the fungus. The high activities of CAT and SOD showed that B. trispora is found under oxidative stress during beta-carotene production. The culture began to show signs of autolysis nearly in the growth phase and autolysis increased significantly during the production phase. The morphological differentiation of the fungus was a result of the degradation of the cell membrane by hydrolytic enzymes and oxidative stress. Increased beta-carotene production is correlated with intense autolysis of clumps, which has as a consequence the increase of the freely dispersed mycelia.