Studies On Hydroxyl Radical Scavenging Ability Of Lentinula Edodes During Lignocellulose Degradation

Lignocellulose and lignin-similar substance can be degraded indefinitely and effectively by white rot fungi through a free radical chain reaction being conducted by ligninolytic enzymes. During the course of degradation, high reactive oxygen species (ROS) concertration was exhibited, and it is worth being discussed that how white rot fungi survive in such an environment and degrade lignocellulose fully. Now, the researches of white rot fungi are focused on their degradation mechanism, and the free radical scavenging abilities of these fungi have been reported little. Thus, the extracellular hydroxyl radical (·OH) scavenging ability of white rot fungi and its characteristics in lignocellulose degradation process were studied in this paper, using the system of"white rot fungus Lentinula edodes strain A3-cornstalk lignocellulose substance- submerged shaking culture". Results are shown below.The oxidative potential and ROS concertration of culture of white rot fungus A3 during lignocellulose degradation were examined, and the damage pressure of free radical on A3 growth was established. Then, the culture filtrate of A3 was proved to have free radical scavenging ability. The·OH scavenging abilities of different white rot fungi, filamentous fungi and bacteria were compared during lignocellulose degradation, and results showed that this scavenging abilities were popular for white rot fungi in a certain extent, whereas were unique contrast to filamentous fungi and bacteria. This abilities were relative to the lignocellulose degradation mechanism and degradation effect of the strains, and could be influenced by substrate components.In-depth studies were carried out on the extracellular·OH scavenging effect of white rot fungus with various media conditions in the dynamic degrading process of lignocellulose, and on the correlation between·OH scavenging and lignocellulose degradation. The·OH scavenging efficiency of A3 reached 45%~50% significantly during biodegrading process. This scavenging ability behaved reversely to ligninolytic enzyme activity (substrate degrading activity) in cultural stage, and preferable·OH scavenging efficiency was exhibited with low enzyme activity and vice versa. Further more,·OH scavenging effect and enzyme activity showed the contrary response (inducement or inhibition) when cultural environment changed. Adding thiourea into the medium stimulated laccase production largely, and the enzyme activity maximum increased to 512 IU/L from 327 IU/L of control with enzyme activity maintained at preferable level for a long time.·OH scavenging ability of A3 was inhibited by thiourea at the same time, and the scavenging efficiency maximum decreased from 50.8% of control to 41.3%. Adding thiourea into culture filtrate had performance opposite to above. In conclusion, white rot fungus could harmonize well the·OH scavenging effect and substrate degrading activity during lignocellulose biodegradation.There were also inner relationship between·OH scavenging effect of white rot fungus and their growth in lignocellulose substrate.·OH scavenging ability of culture of fresh hypha was better than that of culture of aged hypha, and the scavenging efficiency was high when hypha grow fast, vice versa.Crude exopolysaccharides and extracellular crude proteins were the main·OH scavenging substances of white rot fungus A3 on natural cornstalk lignocellulose, and they functioned as a whole. The increase of·OH scavenging efficiency was related with the integration function of the two substances, and the concentration of crude exopolysaccharides and extracellular crude proteins were related with their own·OH scavenging efficiency, respectively. Further more,·OH scavenging specific ability of the culture of white rot fungus could be promoted during lignocellulose degradation process.