The Production Of Hydroxyl Radical Under Different Initial Conditions During The Biodegratation Of Lignin By Phanerochaete Chrysosporium

Lignin biodegradation is an important part of the global carbon cycle. White-rotfungi can secrete extracellular enzymes for degradation of lignin. However largeproteins, such as manganese peroxidase whose molecular weight is greater than40000,are hard through the complete wood cell walls into cells, only after the cell wall isdestroyed by other substances, can enzymes enter secondary wall intercellular layer.So some auxiliary small molecules play a decisive role to lignocellulose degradation.Research shows that in the process of degradation of lignocellulose, anion free radicaland hydroxyl radical and lipid peroxide radicals these three active oxygen groupsplayed an important role. One of the most important is hydroxyl radical (OH), it caneasily oxidation of various organic and inorganic, and response quickly, and has highefficiency. On the other hand, OH can destroy the structure of lignocellulose, andincrease extracellular enzymes’ accessibility to the component of cell wall bycorrosion of wood cell wall.In this paper we take phanerochaete chrysosporium as the research object, usingboth submerged fermentation and solid state fermentation system under the differentinitial conditions. The pH, enzyme activity and free radical content, amount of lignindegradation and the change of the physical and chemical parameters were detected toinvestigate the production of OH during the biodegration of lignin.Under the condition of liquid fermentation, the experimental results show thatin the three kinds of liquid fermentation system, alkali lignin were degradated indifferent degree, and add the hellebore alcohol, manganese sulfat, these smallmolecules oxalate led a better alkali lignin degradation. After10days, concentrationof alkali lignin in the control group was188.2mg/L, group A was180.9mg/L, groupB was166.7mg/L, alkali lignin degradation rate were21.6%,24.6%and30.5%respectively. The lignin degradation rate of Group B is higher than A, indicate thatsmall molecules were beneficial to generate hydroxyl radicals then contribute to thedegradation of lignin. Hydroxyl radical, as a kind of low molecular weight ofantioxidant, it can help open the channel, is conducive to further attacks on lignin by the enzymes.From the perspective of the change of hydroxyl free radical, hydroxylfree radicals content of the two groups increased to the maximum on day2, thendecreased, the same trends were found in the changes of degradation of alkali lignin.For the control group, high concentration of hydroxyl radicals was observed on thefirst two days, which just explains alkali lignin degradation in the control group.In solid state fermentation conditions, the results showed that an appropriateincrease of initial Pb2+concentration could enhance the production of OH during thesolid-state fermentation. The probable reason was that a higher Pb2+concentrationleads to a higher generation of oxalate and O2-, both of which were beneficial to thegeneration of OH. However, when the initial Pb2+concentration reached400mg kg-1,a decrease of OH production was observed, which might be due to the inhibition offungal growth under this condition. In the present of Pb2+, no correlation between OHproduction and lignin degradation were observed, and the related mechanism neededfurther studies.