Extracellular Aerobic Biodegradation Mechanism Of Tetrabromobisphenol-A By Pseudomonas Sp.Fz

Tetrabromobisphenol-A (TBBPA) is one of the most widely used brominated flames retardants in the world. Due to its persistent, bioaccumulative and toxcic, it raises the concerns about its degradation. The biodegradation methods have the advantages of less energy consumption and environment friendly. The existing biodegradation methods of TBBPA mainly contain aerobic and anaerobic treatments. However, little emphasis is placed on the mechanism of TBBPA biodegradation. Nevertheless no information has been available about the active species responsible for TBBPA biodegradation by bacteria up to now.It has been proved that TBBPA often coexists with other organic compounds in the aerobic environment. Therefore, it is significant research on aerobic cometabolism. A bacterial strain named Pseudomonas sp. fz was capable of degrading TBBPA effectively, was isolated from the activated sludge. Under the conditions of pH7.2,150rpm,35℃, and8g/L glucose as carbon sources,10mg/L of TBBPA was removed99.6%after7days cultivation. The article studies on the mechanism of TBBPA degradation via extracellular active compounds secreted by strains fz, and the research of structure and characteristic of this low molecular mass compounds, in order to explain the TBBPA degradation mechanism and understand the fate of TBBPA in the environment.Compared TBBPA degradation efficiency by extracellular, intracellular and periplasmic compounds, it was inferred that the active compounds with high oxidative activity and TBBPA-degrading activity were located extracellularly. Temperature and proteinase K had no effect on the activity of extracellular compounds. Low molecular mass active substances (molecular mass376-456Da) were further purification by ultrafiltration and gel chromatography column.The low molecular mass active substances were peptides composed of aliphatic (Gly and Ala) and aromatic amino acid (Pro) according to analysis of infrared spectroscopy, Raman spectroscopy, nuclear magnetic resonance (NMR) spectrum and Amino acid analyzer. These low molecular mass active substances showed thermostability over a wide range of temperatures (30-80℃), and high activity in the acidic pH range (2.0-5.0). The activity of the low molecular mass active substances was also affected by mental salts, inhibitor (NaN3) and oxygen. Five interminates containing2,6-dibromo-4-(l-hydroxy-enthyl) phenol,2,6-dibromo-4-(2-methoxypropan-2-yl) phenol,2,6-dibromo-4-(prop-l-en-2-yl) phenol,2-monobromophenol, and bisphenol A were identified via the high performance liquid chromatography-mass spectrometry analysis (HPLC-MS). Two simultaneous degradation pathways (isopropyl rupture and debromination) were proposed in the TBBPA degradation by extracellular compounds. Low molecular mass active substances can produce hydroxyl radicals in the process of glucose degradation according to the thiobarbituric acid (TBA) method and Electron Paramagnetic Resonance Spectrometer (ESR) analysis. The properties of low molecular mass active substances also showed that the presence of oxygen, Fe3+, Fe2+, and hydrogen peroxide was conducive to the generation of hydroxyl radicals. And the low molecular mass active substances were able to chelate with Fe3+(Fe2+) and convert Fe3+to Fe2+. Hydroxyl radical was produced by the low molecular mass active substances. The low molecular mass active substances with the substrate universality can degrade TBBPA, bisphenol A, phenol and tribromophenol.