Biodegradation Of Phthalic Acid Esters By Marine Microalgae

Phthalic Acid Esters(PAEs), as a class of common organic pollutants, have been widely detected in coastal waters,while the biodegradation was one of the major removal ways. Marine microalgae were the important primary producer in marine ecosystems, which were able to bioaccumulate and biodegrade organic pollutants. Therefore, the study about biodegradation of PAEs by marine microalgae could provide evidence for assessment of environmental fate of PAEs in marine ecosystems and coast ecological remediation. In this study, biodegradation of two phthalic acid esters(PAEs)-diethyl phthalate(DEP) and di-n-butyl phthalate(DBP) in sediment extracts from Bohai Bay by two marine planktonic algae Dunaliella salina and Chaetoceros sp. and one marine benthic alga Cylindrotheca closterium was investigated. Furthermore, the mechanism was also discussed.The experimental results of DEP and DBP biodegradation under sterile condition showed that when DEP and DBP were mixed, there were no significant changes(p>0.05) of DEP concentrations in algal solutions with D. salina and Chaetoceros sp. during the whole experiment, but a small decrease(18.0%, p?0.05) of DEP concentration in algal solution with C.closterium was observed at the end. Contrary to DEP, biodegradation of DBP by the three microalgal species was fit well to the fist-order kinetic equation and the biodegradation rate constant of DBP in the algal solutions was in the order of C. closterium(0.0169 h-1) >D. salina(0.0035 h-1) and Chaetoceros sp.(0.0034 h-1), which indicated C. closterium was the most effective species, while the performance of D. salina and Chaetoceros sp. was comparable. However, there was no significant relationship between biodegradation efficiency of the PAEs by the three microalgal species and activity of esterases participating in initial hydrolysis of PAEs, suggesting that PAEs loss from the algal solutions was possibly correlated with certain esterases. Biodegradation of single DEP in algal solutions by three species was much more obvious compared with that in the presence of DBP. At the end of the experiment, the degradation efficiencies of DEP by D. salina, Chaetoceros sp. and C. closterium were 32.3%, 26.3% and 81.2%, respectively, which indicated that DBP had inhibitory effect on biodegradation of DEP by three microalgal species.In the biodegradation of DEP-DBP mixture by single bacteria and algae-bacteria systems, DEP was only not degraded obviously by single bacteria. Contrarily, DBP was significantly decreased, the biodegradation rate of which was higher than that of DEP. In algae-bacteria systems, the growth of bacteria was inhibited. Similarly, the growth of D. salina was also inhibited. However, the growth of Chaetoceros sp. and C. closterium was enhanced. In D. salina-bacteria system, degradation of DBP was from the effort of D. salina and bacteria. In Chaetoceros sp.-and C. closterium-bacteria systems, biodegradation of DBP was mainly from the contribution of Chaetoceros sp. and C. closterium, respectively.Moreover, degradation of DEP and DBP in both extra- and intracellular crude extracts containing enzymes was investigated. The results showed that DEP and DBP were able to be degradated by both extra- and intracellular crude extracts and the degradation trends were similar to those in algal solutions. At the end of the PAEs biodegradation experiment by three microalgal species, DEP was largely in water phase(93.3~100.0%), while DBP remained in both water(65.3~78.0%) and algal phase(22.0~34.7%) because DEP is more water-soluble. Thus, it can be concluded that biodegradation of DEP by the algae was mainly due to degradation by extracellular enzymes, and both extra- and intracellular enzymes played key roles in the degradation of DBP.