Study On Production Of Substances Eliminating Free Radicals During Lignocellulose Degradation By White Rot Fungi

White rot fungi are effective microbes that have strong potential to degrade lignocellulose now. They produce lots of activated free radicals such as hydroxyl radicals(·OH) for helping ligninolytic enzymes to degrade lignocellulose better. White rot fungi can protect themselves from the damage of free radicals, the mechanism involved is worth studying. Firstly, preponderant fungus A3(Lentinus edodes) was chosed from four white rot fungi, because it had better advantage in growth, better ability to secrete laccase and best ability to produce substances that could eliminate free radicals. And simultaneity, cornstalk was filtrated as experimental material from three straws. The system of study was founded. It was showed in the study on extracellular substances eliminating free radicals of fungus A3 that the component and proportion of extracellular substances eliminating free radicals were diverse in different mediums. In the basal medium, crude exopolysaccharides was the main component of extracellular substances eliminating free radicals. And in the lignocellulose medium, crude exopolysaccharides also was the main component of extracellular substances eliminating free radicals, but their proportion declineed to some extent, and the proportion of protein portion in crude exopolysaccharides rose. In the lignocellulose medium, there were some other substances eliminating free radicals which had some relations with lignocellulose biodegradation. It was showed in the study on endocellular substances eliminating free radicals of fungus A3 that the main component of endocellular substances eliminating free radicals in different mediums all were endopolysaccharides and protein, but their proportion were diverse in different mediums. Moreover, there were some other substances eliminating free radicals except for endopolysaccharides and protein, and they accounted for about 15% in endocellular substances eliminating free radicals. In the same medium, the mass of exopolysaccharides was obviously more than that of endopolysaccharides of fungus A3, furthermore, the ability to eliminate free radicals of exopolysaccharides also was stronger than that of endopolysaccharides. After the protein were removed, the eliminating efficiency to hydroxyl radicals of crude exopolysaccharides and endopolysaccharides dropped to some extent, it showed that the protein portion of crude polysaccharides had considerable effect on the ability to eliminate hydroxyl radicals of crude polysaccharides. In the lignocellulose medium, the content and the unit ability to eliminate hydroxyl radicals of extracellular and endocellular substances eliminating free radicals changed congruously with ligninolytic enzymes activities on the whole. Lignocellulose could promote the production of extracellular and endocellular substances eliminating free radicals, and thiourea which was a sort of reagent eliminating free radicals could restrain the promotion to a great extent. It showed that the production of extracellular and endocellular substances eliminating free radicals of fugus A3 had some relations with lignocellulose biodegradation and the concentration of free radicals in the culture environment. The main significance of white rot fungi producing substances eliminating free radicals during lignocellulose degradation was that white rot fungi could found effective extracellular and endocellular defensive system by secreting various extracellular and endocellular substances eliminating free radicals such as polysaccharides, SOD, therefore they could protect themselves from free radicals during lignocellulose degradation. The thesis studied firstly the production of extracellular and endocellular substances eliminating free radicals during lignocellulose degradation by white rot fungi, ascertained the component,character and dynamic changing law of extracellular and endocellular substances eliminating free radicals of white rot fungi, and discussed the mechanism of white rot fungi defending against free radicals during lignocellulose biodegradation, which has important theoretic and practical significance.