Characterization And Preliminary Mechanism Study Of A Halotolerant Azo Dye Degrading Fungus Induced By Static Magnetic

Azo dyes are common water pollutants due to their wide application.Furthermore,high loading of salts increase the difficulty of their treatment.It is shown in many researches that metabolicmechanisms,enzymaticactivityandcellmembranepermeabilityof microorganisms could be promoted by magnetic field.Thus it is expected that treatment efficiency and stability of traditional wastewater treatment processes can be enhanced.Basing on the above illustration,this study aimed at promoting treatment efficiency and stability of hypersaline azo dye wastewater by the biological method.In addition,pure strains which could be stimulated by magnetic field were tried to isolated and further mechanisms were also discussed.The effect of static magnetic field?SMF?on a marine microbial community?MMC?for treating hypersaline azo dye wastewater was firstly studied.The results showed that Acid Red B?ARB?decolorization,COD removal,detoxification,biomass proliferation processes,as well as halotolerance of MMC were all enhanced by 45.3 mT SMF.High throughput sequencing technology was used for analyzing the microbial community structure and the results showed that some bacterial and fungal genera were identified as dominant ones in the MMC community with 45.3 mT SMF,which might be related to the increase of ARB degradation efficiency.Subsequently,a halotolerant yeast named as SYF-1 which was capable of degrading azo dyes was isolated from the MMC community with 45.3 mT SMF.The yeast SYF-1 was identified as Candida tropicalis through 26S rDNA sequencing method.Then effects of different parameters on degradation of ARB by growing cells of the yeast SYF-1 were investigated and the results showed that the optimal conditions were as follows:at least 4.0 g/L glucose,0.6 g/L?NH₄?₂SO₄ and 0.08 g/L yeast extract;not higher than 30 g/L NaCl,at least 160 r/min rotation speed,30?and pH of 7.0-8.0.It was suggested that Candida tropicalis SYF-1 was a mesophilic yeast which preferred neutral and weak alkaline conditions.In addition,degradation pathway of ARB by the yeast SYF-1 was proposed as that consisted of reduction,monooxygenase-oxidization,reductive/oxidative deamination,oxidative desulfurization and ring-cleavage processes.Furthermore,acute toxicity of ARB was obviously reduced after degradation.Basing on the results of characteristics study,the effect of SMF on growing and metabolic activity,as well as halotolerance of the yeast SYF-1 was studied.The results showed that decolorization efficiency,growth rate and halotolerance of the yeast SYF-1 were higher when exposed to SMF of certain intensity than those without SMF.The optimal performance was observed when SMF intensity was 95.0 mT.However,SMF of higher than95.0 mT displayed inhibition effects.Morphology of cells with different SMF intensity was observed by scanning electron microscopy?SEM?.The result showed that slight depression appeared on cell surface when exposed to 95.0 mT SMF.In comparison,cell surface was damaged when exposed to SMF of higher than 95.0 mT.Meanwhile,the effect of 95.0 mT SMF on activities of key enzymes and composition of cell membrane was also investigated.The results showed that the activity of NADH-DCIP reductase for decolorizing azo dyes by the yeast SYF-1 was hardly influenced by SMF.In comparison,activities of two important oxidases:lignin peroxidase?LiP?and laccase?Lac?were obviously increased by 95.0 mT SMF.Furthermore,activities of all the three key enzymes were only detected intracellularly.Under hypersaline conditions,the relative abundance of total unsaturated fatty acid in cell membrane was higher when exposed to 95.0 mT SMF than that without SMF.It was suggested that cell composition under hypersaline condition was regulated to that with lower salinity by 95.0 mT SMF,thus relatively high fluidity of cell membrane was maintained,which was related to high metabolic activity.