Preliminary Study On The Degradation Charicteristics And Mechanisms Of Two Kinds Of Polycyclic Aromatic Hydrocarbons(PAHs) By Green Algae Chlamydomonas Reinhardii

Phenanthrene?Phe?and Benz?a?anthracene?BaA?belong to polycyclic aromatic hydrocarbons?PAHs?.They are defined as combined aromatic compounds with two or more benzene rings and their derivatives,which are a group of carcinogenic and mutagenic persistent organic pollutants?POPs?distributing in a variety of ecological habitant.The pollution of PAHs has been responsible for numerous adverse impacts on humans and environment.In recent years,PAHs were detected as a serious pollutant in freshwater around the world and the concentration in surface water ranged from245.46ng L^-11 to 1074.40ng L^-1.The concentration of Phe and BaA in surface water was above the pollutant limits.Green algae are primary photosynthetic organisms and the most important oxygen producers distributing in various habitats even in extreme environments.As the first sequenced green alga,Chlamydomonas reinhardii was investigated intensively in the different biological fields,including the genes function,photosynthesis,organelle,cell cycle control and so on.In this study,the efficiency of Phe and BaA degradation by C.reinhardii was studied,the expression of genes and activity of enzymes as well as the the intermediate metabolites were analyzed.Moreover,the mechanism of the degradation was speculated.The high degradation efficiency of the two PAHs by the C.reinhardii suggests that the green algae may be a sustainable candidate for PAHs remediation.The main research results of this study are shown as follows:1.Studies on different concentration(mg L^-1)of Phe and BaA on the growth of C.reinhardii.Under 10 mg L^-1 of Phe,the growth was almost equivalent to that of the control without Phe(0 mg L^-1).However,higher concentration above 30 mg L^-1 of Phe inhibited the growth obviously and 50 mg L^-1,100 mg L^-1of Phe inhibited completely.Under 10 mg L^-1 and 30 mg L^-1 of BaA,the growth was comparable to that of the control(0 mg L^-1 BaA).Similar as Phe,higher concentration above 50 mg L^-1 of BaA inhibited the growth dramatically.10 mg L^-11 of Phe and BaA was chosen to be the concentration in the degradation experiments.The activity of superoxide dismutase?SOD?and Catalase?CAT?of C.reinhardii during the degradation was also determined,and it was found that SOD and CAT activity was higher in the co-culture system containing Phe than in the culture system containing BaA,which showed that the toxicity of Phe to C.reinhardii was greater than that of BaA.2.Studies on the degradation charicteristics of Phe and BaA by C.reinhardii.100%of the Phe and the BaA with concentration of 10 mg L^-1 was degraded by C.reinhardii in 8 days and 11 days,respectively.The concentration of Phe and BaA were declined gradually,while the intracellular Phe and BaA kept at a low percentage,indicating that the C.reinhardtii degraded Phe and BaA.In this study,Phe and BaA were degraded by C.reinhardii with a significantly higher efficiency compared with the previous study by other microorganisms.The degradation of Phe and BaA by C.reinhardtii was affected by the environmental factors and the best condition was tested to be 25?and initial pH at 6.0.3.During the degradation of Phe and BaA,their intermediate products were assayed by a GC-MS,which were different from the previous studies,suggesting a new degradation pathway involved in the Phe and BaA degradation and a brief degradation pathway was predicted according to the experimental results.4.In the degradation process,transcriptomic analysis was conducted,Among the Up-regulated genes,hmgA,cmbL,rbcS and aox1 was detected.The expression of the genes was determined and verified by qRT-PCR.At the same time,the activities of homogentisate 1,2-dioxygenase?HGD?and Ribulose bisphosphate carboxylase oxygenase?Rubisco?were determined during this degradation process.These enzymes showed higher activities than the control.The results indicated these important genes and enzymes might participate in the degradation process.In conclusion,Chlamydomonas reinhardii is determined to degradate the Phe and BaA.The degradation characteristics and mechanism of two kinds of PAHs by C.reinhardii were stuied and analyzed,including the intermediate metabolites,the gene expression,the activity of enzymes.This study may provide more knowledge and insights in studying the degradation of PAHs in the water system and the mechanism in the molecular level.