Degradation Characteristics Of Phthalate Esters (PAEs) By Deep-sea Fungi

Dimethyl phthalate esters (DMPEs) which belong to the family of phthalic acid ester (PAEs) are used extensively in the manufacturing of plastics that contributes to the environmental pollution. In this study, two DMPEs-degrading fungi Mar-Y3 and IR-M4 were isolated from the deep sea sediments at depth of 2948 m from Atlantic Ocean and depth of 3300 m from Indian Ocean, respectively. Based on microscopic spore morphology and ITS rDNA gene sequence analysis, the fungal Mar-Y3 was identified as Rhodotorula mucilaginosa Mar-Y3 (KM052362) and the fungal IR-M4 was identified as Aspergillus versicolor IR-M4 (KM052361). In order to compare the biodegradation of three isomers of DMPEs which are dimethyl phthalate (DMP), dimethyl isophthalate (DMI) and dimethyl terephthalate (DMT), investigations were carried out with these two deep sea fungi.To R. mucilaginosa Mar-Y3, the study showed that DMPEs were utilized by R. mucilaginosa Mar-Y3 as the sole source of carbon and energy. Instead of mineralizing DMPEs completely, this yeast transformed them to their further degradation products. The pathways for R. mucilaginosa Mar-Y3 to degrade these three DMPE isomers were apparently different. The yeast transformed DMP and DMI to its monoesters (MMP and MMI, respectively) with one-step ester hydrolysis, but no more ability to transform MMP and MMI. Meanwhile, the deep sea yeast proceeded two-step ester hydrolysis for DMT:firstly, quickly transformed DMT to MMT and then hydrolyzed MMT to TA. The different pathways of DMPEs degradation by this deep sea yeast are shown in this study, indicating that the esterases which are the key for hydrolysis have highly specific on substrate.To A. versicolor IR-M4, the study showed that the fungal can utilize DMI and DMT as the sole source of carbon and energy to transform them to the corresponding monomethyl phthalate or phthalic acid, but cannot degrade the DMP. The pathways for A. versicolor IR-M4 to degrade DMI and DMT were also different. The fungal proceeded DMI to its monoesters (MMI) with a high speed by one-step ester hydrolysis and no further metabolism. Meanwhile, DMT was mineralized by the deep sea fungal to MMT and subsequently to TA with the second ester bonds hydrolysis. The different pathways of DMPEs transformation by A. versicolor IR-M4 are also discovered in this study, suggesting that the substrate specificity of its esterases is very high.As the two experiments showed these two deep-sea DMPEs-degrading fungi cannot mineralize the phthalic acids (PA, IA, TA), we decided to isolate some deep sea fungi which have the ability to degrade the phthalic acids in order to the further research of degrading PAEs completely and the study of dioxygenase. Finally,13 fungi strains were isolated from two deep sea sediment samples located at the depth below 5000 m in northeastern Pacific Ocean. The 13 fungi strains can use the PA/IA/ TAas the sole source of carbon and energy and degrade it.To our best knowledge, either to R. mucilaginosa or A. versicolor isolated from deep sea sediments, this study is the first report to discuss their biodegradations of three isomers of DMPEs. This study showed that the fungi isolated from deep sea sediments have great potential on biodegradation of DMPEs pollution.