Biodegradation Characteristics Of Phthalates Degrading Strain Acinetobacter Sp.LMB-5 And Properties Analysis Of The Esterase

Phthalate acid esters（PAEs）are common plasticizer with good plasticity and low cost.They are widely used in various fields,such as food,cosmetics,construction.However,PAEs migrate to environment during the process of production,employ and treatment.The amount of PAEs is increasing in the river,soil and air.PAEs are difficult to be degraded and pernicious to human health.Degradation of PAEs by microorganism does not form secondary pollution and is friendly to the environment.Therefore,it is promising and meaningful to degrade PAEs by microbes.We have screened a PAEs degradation bacterium-Acinetobacter sp.LMB-5 from a vegetable greenhouse which has been polluted by plastic film for many years.We have studied the basic morphological properties.In this dissertation,we made more study on LMB-5.When LMB-5 degraded DMP,DEP,DBP and DEHP,the results showed that degradation efficiency increased if the side chains of PAEs were uncomplicated.To study the optimum culture conditions,the results shown that the optimum temperature for degradation of PAEs was 37℃and the optimum pH was 6.0.When the concentration of DBP increased from 100 to 400 mg/L,the degradation ability of strain LMB-5 could be described by first-order kinetics.To study the pathway of DBP degradation by LMB-5,according to the experiment,strain LMB-5 could generate BMP and DMP by oxidization,then strain LMB-5 hydrolyze ester bonds to form PA,and further metabolize to other compounds.After analysis of the whole genome of LMB-5,an important hydrolase Est₃563 was excavated.It could transform DBP into monoester MBP.The expression vector was constructed in vitro to obtain the target protein.And the basic enzymatic properties were studied.The optimum temperature and pH of Est₃536 was 40 ℃ and 6.0.Organic reagents such as ethanol,acetonitrile and ethyl acetate inhibited the activity of Est₃563.Metal ions Zn2+,Mn2+,Ca2+and Mg2+ had inhibitory effect on the activity of Est₃563,but Cu2+ and Fe3+ could improve the hydrolysis of Est₃563.Tertiary structure was built by homology modeling,and the reliability of the model was determined by software evaluation.Molecular docking indicated that ligand DBP could enter the active pocket of Est₃563.