Influences of nutritional conditions on degradation of dibutyl phthalate in coastal sediments with Cylindrotheca closterium

First identification and characterization of detoxifying plastic-degrading DBP hydrolases in the marine diatom Cylindrotheca closterium

Diatoms are photosynthetic organisms with potential biotechnological applications in the bioremediation sector, having shown the capacity to reduce environmental concentrations of different pollutants. The diatom Cylindrotheca closterium is known to degrade di-n-butyl phthalate (DBP), one of the most abundant phthalate esters in aquatic environments and a known endocrine-disrupting chemical. In this study, we present for the first time the in silico identification of two putative DBP hydrolases (provisionally called DBPH1 and DBPH2) in the transcriptome of C. closterium. We modeled the structure of both DBPH1-2 and their proposed interactions with the substrate to gain insights into their mechanism of action. Finally, we analyzed the expression levels of the two putative hydrolases upon exposure of C. closterium to different concentrations of DBP (5 and 10 mg/l) for 24 and 48 h. The data showed a DBP concentration-dependent increase in expression levels of both dbph1 and 2 genes, further highlighting their potential involvement in phthalates degradation. This is the first identification of phthalate-degrading enzymes in microalgae, providing new insights into the possible use of diatoms in bioremediation strategies targeting phthalates.

Oxidative stress responses caused by dimethyl phthalate (DMP) and diethyl phthalate (DEP) in a marine diatom Phaeodactylum tricornutum

A marine diatom (Phaeodactylum tricornutum) was exposed to different concentrations of dimethyl phthalate (DMP) and diethyl phthalate (DEP) for 96 h within a batch-culture system to investigate their toxicities. Results showed that P. tricornutum could remove DMP and DEP effectively with removal rates of 0.20-0.30 and 0.14-0.21 mg L^-1 h^-1, respectively. In addition, DMP and DEP significantly inhibited the photosynthesis and chlorophyll a biosynthesis of P. tricornutum with 96-h EC₅₀ values of 390.5 mg L^-1 and 74.0 mg L^-1, respectively. Results of reactive oxygen species (ROS) level suggested that the two PAEs could induce excessive ROS production in the diatom. Moreover, activities of antioxidant enzymes (i.e., SOD and POD) in the diatom increased with the increase of DMP and DEP concentrations. The results will help to understand the toxic mechanisms of PAEs, and provide strong evidences for evaluating their ecological risks in the marine environment.