|M.Sc Student||Felikstain Nufar|
|Subject||The Role of Oxygen in the Induction of Synthesis of Lignin|
Peroxidase (LIP) in White Rot Fungi Phanerochaete
|Department||Department of Biology||Supervisors||Professor Emeritus Shimon Gepstein|
|Professor Carlos Dosoretz|
The white-rot fungus Phanerochaete chrysosporium is known for its exceptionally high ability to degrade and metabolize lignin as well as a broad range of recalcitrant organopollutants by an oxidation catalyzed by extracellular peroxidases: lignin peroxidase (LIP) and manganese peroxidase (MnP). Expression of LIP in liquid cultures of P. chrysosporium requires nutrient starvation as well as exposure to a pure oxygen atmosphere, which may lead to increased production of reactive oxygen species (ROS), suggesting that the fungus might be under oxidative stress. Thus, the current research focused on studying the effect of molecular oxygen in LIP producing (i.e, ligninolytic) cultures of P. chrysosporium and the roles of oxygen and its derivatives in the synthesis of LIP. High steady state concentrations of ROS, enhancement of antioxidant enzyme activities and accumulative damage in cells in ligninolytic cultures, indicated the existence of oxidative stress. Moreover, it was found that the levels of ROS were directly correlated to LIP production, suggesting that ROS may play a role in the induction of LIP genes expression. In ligninolytic cultures of the fungus, which were grown in the presence of dimethyl sulfoxide (DMSO), a scavenger of hydroxyl radical, neither LIP activity, nor LIP izoenzymes production, nor lip H2 transcripts were detected. The results strongly suggest, that hydroxyl radical is involved in the induction of LIP gene transcription.
In conclusion, this work showed the importance of ROS and particular hydroxyl radical existence in the fungi, in addition to starvation conditions, for production of high levels of LIP.