Study On Ligninolytic Enzyme System Of White Rot Fungi And The Biotoxicity Of Reactive Black KN-B

White rot fungi are capable of degrading many persistent poIIutants.The degradation process relies on the extracellular ligninolytic enzyme system. The paper focuses on the ligninolytic enzyme system of basidiomycete Phanerochaete chrysosporum and the biotoxicity of Reactive Black KN-B (RB KN-B) on P. chrysosporum. The biodegradation of RB KN-B by P. chrysosporum was assayed, and the toxic effects of RB KN-B on Manganese-dependent Peroxidase (MnP) activity and cellular ultrastructure of P. chrysosporum was studied. Furthermore, we observed the ligninolytic enzyme of a new basidiomycete and it's detoxicative effects on mixture of reactive dyes.The results are as follows:1. Under the cultivation condition of our lab, the activity of MnP and laccase (Lac)of P. chrysosporum could be detected after 4 days cultivation and increased to a peak on the seventh day of cultivation. The activity of LiP could not be detected during the cultivation period.2. Absorbance spectrum of cocultivative solution of P .chrysoporum with RB KN-B showed that, with the treatment of P .chrysoporum, the absorbance at 598 nm decreased significantly, which indicated the elimination of RB KN-B. Meanwhile, the wavelength of maxium absorbance of the cocultivative solution shifted from 598nm to 525nm and 556nm, and the absorbance spectrum in ultraviolet band also presented significant changes. These results indicated that biodegradation of RB KN-B existed under the treatment of P.chrysoporum.3. At the concentration of 50 mg/L, RB KN-B could induce higher MnP activity. At 200, 350 and 500 mg/L, activity of MnP was remarkably decreased during the whole observation period, and the inhibition effect enhanced with the increase of RB KN-B concentration. In the range of low concentration of RB KN-B (20-80mg/L) , MnP activity underwent a time course of increasing early and decreasing later.4. Acute toxicity test performed on luminescent bacteria and micronucleus test on V.faba root tips indicated that RB KN-B was acute toxic and mutagenic.5. After exposure to RB KN-B for 10 days, the ultrastructure of hyphal cells was evidently damaged. The changes included plasma membrane separating from cellular wall and cytoplasm coagulating. The obvious cellular autolysis was observed at 500 mg/L. The above adverse effects became more evident with the increase of RB KN-B concentration.6. A new basidiomycete (named as 12# mutant temporarily) was preliminarily explored in this paper. No ligninolytic enzyme activity was detected when 12# mutant was cultivated in different cultivation conditions. However LiP, MnP and Lac enzyme activity could be detected when 12# mutant was cultivated with mixture of reactive dyes in the bioreactor. , The mutagenicity of mixture of reactive dyes was significantly decreased after the treatment by 12# . mutant in the bioreactor. When at 100mg/L, the acute toxicity of mixture of reactive dyes was decreased by the treatment of 12# mutant in the bioreactor, however no notable change on the acute toxicity when at 400 mg/L.The results above suggest that Phanerochaete chrysosporum is capable of degradinge RB KN-B and MnP might serve as the key enzyme involved in the biodegradation. As a toxic exogenous agent, RB KN-B may have an adverse influence on P.chrysosporum at the aspects of biochemistry and morphology. Cocultivated with RB KN-B, P.chrysosporum underwent a stress response which manifested three stages of inducement, inhibition and exhaustion at the level of MnP activity. RB KN-B could induce untrastructural damage in P.chrysosporum and these morphological changes were relevant to the alteration of MnP activity. It is suggested that the production of MnP might be one of stress response in P.chrysosporum under threatening environmental factors such as RB KN-B. 12# mutant could produce ligninolytic enzyme in the symbiotic system of bioreactor. There were evidences that the bioreactor of 12# mutant had the potential to reduce toxicity of mixture of reactive dyes.