Characterization Of Phthalate-degrading Bacterial Strain And Its Application In Phthalate-Contaminated Soil

Phthalic acid esters?PAEs?are commonly used as plasticizers in industry and are easily released into the environment during the production and use of plastics.Because of its carcinogenicity,teratogenicity and mutagenicity,it has great harm to human health.In recent years,with the wide application of agricultural plastic films,more and more PAEs have been released into agricultural soils.The content of PAEs in some typical covered farmland soils in China is much higher than the control standards of soil PAE compouds in the United States.Therefore,it is very necessary to remedy PAEs contaminated soil.At the same time,the key to successful remediation of contaminated soils is to screen out highly-efficient PAEs-degrading bacteria with strong environmental adapability.In the present study,acclimated and screened PAEs-degrading bacteria from activated sludge,studied their degradation characteristics,speculated their metabolic pathways to PAEs,and studied their their remediation effect on PAEs-contaminated soils,providing a theoretical basis for the actual bioremediation of contaminated soils.The main findings are as follows:?1?obtained highly-efficient PAEs-degrading strain and bacterial consortium:a di-2-ethylhexyl pgthalate?DEHP?-degrading bacteria?named ASW6D?and a bacterial consortium?B1?capable of degrading dibutyl phthalate?DBP?was obtained fome the activated sludge.Based on 16S rRNA sequence analysis,the bacterial strain was identified as Mycobacterium sp.?Genbank:KY888692?.Community analysis revealed that the predominant genus of consortium B1 was Pandoraea and the rests were Microbacterium,Flavisolibacter,Gordonia,Comamonas and so on.?2?the strain ASW6D can efficiently degrade DEHP and has high adaptability to environmental factors such as temperature and pH:DEHP can be efficiently degraded at a temperature of 20–40°C and a pH of 5–10;ASW6D could degrad 100 mg/L DEHP by 89.34%within 24 h,and degrad 500 mg/L DEHP by more than 82.87%within 3 d.Further,ASW6D also utilized dimethyl phthalate?DMP?and dibutyl phthalate?DBP?as carbon sources.The metabolites of DEHP degradation were further analyzed by Gas Chromatography-Mass Spectrometer?GC-MS?.The metabolic pathway of DEHP was as follows:initially the side chain of DEHP was shortened by?-oxidation,and then DBP was formed;DBP was then converted to phthalic acid?PA?by hydrolysis;PA oxidizes to open the ring and eventually enters the tricarboxylic acid cycle to produce CO₂ and H₂O.?3?the consortium B1 can efficiently degrade DBP and can efficiently degrade DBP under a wide temperature and pH range:when the DBP concentration is not higher than 500mg/L,the mixed bacteria B1 can degrade DBP by 90%within 3 d;when the initial concentration is no more than 500 mg/L,DBP was efficiently degraded by consortium B1,with the degradation rate above 90%within 3 d.In addition,B1 can efficiently degrade DBP?35 mg/L?over a wide range of temperature?20–40°C?and pH?4.5–10.5?.Apart from DBP,consortium B1 could also utilize dimethyl phthalate?DMP?and di-2-ethylhexyl pgthalate?DEHP?as the sole carbon and energy source.The addition of different carbon sources has a certain effect on the utilization of DBP by B1,but it does not affect the final removal rate of DBP.The results of GC-MS analysis showed that PA was the only intermediate product detected during the degradation of DBP,and that PA could also be utilized by mixed B1.?4?bioremediation of PAEs-contaminated soil by ASW6D and B1:degrading bacteria ASW6D and consortium B1 can survive in the PAEs-contaminated soil,and the addition of ASW6D and B1 greatly improve the removal rate of DEHP and DBP in the soil,suggesting that the degrading bacteria ASW6D and consortium B1 have potential for the bioremediation of PAEs-contaminated soil.