Study On The Mechanisms Of The Promotion Of Dye Decolorization By White Rot Fungi With Lignin As Co-substrate

Azo dyes are widely used in the global textile industries,which pose significant environmental and human health hazards.Even though some bacterials fungi,especially white rot fungi are well known for their outstanding capability in the degradation of dyestuffs,inefficient removal of dyes is still the the bottlenecks for their application due to the dyes' structural diversity and refractory characteristics.Based on this,the study focused on investigating whether lignin could promote the fungal degradation of recalcitrant dyes through the extracellular non-specific ligninolytic enzymes induced by lignin.The lignin-dye co-substrate system was established to enhance the degradation of dyes by white rot fungi,and the molecular mechanisms of rapid dye degradation in the present of lignin were also discussed,the main research results were discussed as follows:Different species of white rot fungi were selected to investigate the degradation efficiency of different dyes with lignin as co-substrate.The results showed that the dye degradation efficiency was notablely increased in presence of lignin.In case of azo dye DR5 B,the decolorization rate was increased by 34.2%(2d)and 54.8%(3d)by white rot fungi Ganoderma lucidum EN2 and Irpex lactues CD2 with lignin as co-substrate,respectively.Meanwhile,the decolorization rate of triphenylmethane dye CV was increased by 44.1%(3d)and 47.1%(2d),respectively.Further research on the decolorization of different kinds of dyes was carried out in the presence of lignin by G.lucidum EN2 and I.lacteus CD2,which confirmed the universal promotion effect of lignin in dyes removal by white rot fungi.The decolorization rate of DR5 B,RB5,DB71,DB38,DB22,CV and BB increased by 30%~50% and 38%~55% by G.lucidum EN2,and I.lactues CD2,respectivity.The mechanisms of effective degradation of DR5 B by aforementioned two typical white rot fungi in lignin/dye co-substrate system were studied.It was revealed that G.lucidum EN2 and I.lactues CD2 use different approaches to accelarate dye degradation with lignin as co-substrate.In case of G.lucidum EN2,the rapid degradation of DR5 B in presence of lignin was due to the enhancement of extracellular laccase activity which was domenstrated to be the key ligninolytic enzyme involved in DR5 B degradation.In addition,the studies of invitro experiments combined with GC/MS analysis of metabolites from lignin degradation by G.lucidum EN2 was carried out to further show that the enhancement of laccase activity were related to the small aromatic molecular derived from lignin degradation.Some of the small molecular phenol compounds such as guaiacol could act as laccase mediator to accelerate the dye degradation.I.lacteus CD2 is another unique strain which has never been detected for laccase activity,transcriptomics and proteomics were applied to elucidate the molecular mechanisms for the degradation of azo dye DR5 B by I.lacteus CD2 in presence of lignin.The result showed,first of all,many aromatic polymer degradation-relevant enzymes were coordinately up-regulated under lignin/dye co-substrate system,including ligninolytic enzymes,the metal binding and ion transporter related proteins,as well as some extracellular oxidoreductases that could generate H2O2.Secondly,besides the lignolytic enzymes,Fenton reaction based on hydroxyl radical and iron might also play a critical role in DR5 B and lignin degradation.Meanwhile,Manganese perioxidase(Mn P)was found to be the key enzyme required for the rapid degradation of DR5 B degradation by I.lacteus CD2,which was further confirmed by in vitro dye degradation assay with purified Mn P.The “omics” analysis also showed that the aromatic compound catabolism related enzymes including homogentisate 1,2-dioxygenase were significantly overexpressed in co-substrate system which was believed to be the key enzymes for the degradation pathway in I.lacteus CD2.The result showed that the effective degradation of dye in co-substrate system was carried out by a complex network of enzymes,redox system and co-factors.In summary,this study established an effective dyes biodegradation system with lignin as co-substrate by white rot fungi and revealed the molecular mechanisms and dynamic degradation process for effective aromatic compounds degradation,which not only provides technical support and theoretical basis for biomass and xenobiotics degradation for application,but also inspire a new thought for the efficient degradation for environmental pollutants by white rot fungi.