Property And Mechanism Of Decabromodiphenyl Ether Biodegradation By Brevibacillus Brevis

Decabromodiphenyl ether (BDE209) is a ubiquitous persistent pollutant and hascontaminated the environment worldwide. To accelerate BDE209elimination and revealthe mechanism concerned, the enhanced biodegradation of BDE209by Brevibacillusbrevis through acceleration of surfactants tween80and tea saponin was conducted, aswell as the changes of microbial cell surface features and BDE209biodegradationmechanism.The results revealed that B. brevis was an efficient strain to degrade BDE209inmineral salt medium. The removal efficiency of0.5mg/L BDE209by1g/L biomass wasup to48%within5d. When the concentrations of Na2HPO4, KH2PO4, NaCl and(NH4)2SO4in the mineral salt medium were90,10,40and30mg/L, respectively, thedegradation effect was favorite. The optimum conditions of BDE209biodegradation were130r/min shaking speed,5d contact time and1g/L biomass, separately.When surfactant concentrations were60mg/L, tween80and tea saponin both hadpreferable solubilization on BDE209and increased the BDE209solubility in water byabout130times compared with the control. Surfactant and B. brevis had joint positiveeffects on BDE209degradation. The degradation rate was up to about55%as theconcentration of surfactant was20mg/L. The result indicated that removal process ofBDE209included surface biosorption, active transport and biodegradation. Thebiodegradation capacity increased notably as time increased and biodegradationequilibrium nearly arrived within5d. B. brevis could release Na+, NH4-, Cl-and NO2-, andabsorb PO43-, SO42-, K+and Mg2+during BDE209biodegradation. The result also revealedthat surfactant at high levels used in the current experiments enhanced the release of someintracellular ions and depressed the utilization of certain extracellular nutrient ions.After degradation of BDE209, the surface of B. brevis was wrinkled, becamedepressed and induced cell adhesion as time passed. Although the strain cell membranechanged in permeability after treatment of pollutants, resulting in outflow of thecytoplasm, the strain still had reproductive function. The presence of BDE209couldstimulate B. brevis cell growth and increase its bioactivity. Polysaccharides, proteins and lipids in the cell membrane participated in BDE209biodegradation. The combined effectsof intracellular and extracellular enzymes, generating by B. brevis, could effectivelydegrade BDE209.GC-MS analysis revealed that the structure of BDE209was changed by the strain, andgenerated nonabromodiphenyl ethers (BDE208,207and206), octabromodiphenyl ethers(BDE203,197and196) and heptabromodiphenyl ether (BDE183) by debromination. Theamount of BDE209degraded was significantly more than that of the total detectedmetabolites, confirming that the decrease of BDE209concentration was not only due tothe debromination pathway, but also the elimination of the aromatic ring structure ofBDE209.