Research On The Bap Biodegradation By S. Maltophilia In BaP-Cu²⁺ Combined Pollution System And The Effects Of Pollutants On Characteristics Of S. Maltophilia Cell

To illuminate the characteristics and mechanisms involved in benzo[a]pyrene (BaP)biodegradation in the polluted environment where BaP and Cu²⁺co-existed, this study hasfocused on the bio-treatment of BaP and Cu²⁺in various combinations byStenotrophomonas maltophilia, which was isolated from the sediments of the e-wastecontamination. The experimental biodegradation of BaP was carried out in single andcombined pollution system simultaneously to discusse the properties and metabolicpathways of BaP biodegradation. Changes of cell surface features of S. maltophilia werealso investigated to determine the characteristics and mechanisms of co-contaminationbio-sorption/biodegradation.In the presence of BaP and Cu²⁺in the culture medium, the bacterium experienced a2ndgrowth and the cell biomass increased slowly after48h. S. maltophilia could utilize BaPas carbon and energy to promote growth directly when there was no external carbonsource in MSM. And the presence of Cu²⁺was beneficial for S. maltophilia to make useof BaP.S. maltophilia is an effective strain to remove BaP and Cu²⁺from solution, and thedegradation efficiency of BaP increasing over time. The concentrations of BaP and Cu²⁺in extracelluar solution declined rapidly after4h, while the pollutants content in the cellsincreased slowly and remained stable after48h. Finally, the concentration of BaP in cellwas0.14mg·g-1, but the Cu²⁺contents inside and outside bacterial cells were maintainedat0.99-1.50mg·g-1. The degradation efficiency of about45.38%within3d was achievedwhen dealing with1mg·L-1BaP under initial natural pH at30℃, and this degradation rate reached48.01%in2d at35℃.The favorable temperature and pH for BaP removalwas25℃and6.0respectively, when Cu²⁺coexisted in the solutions. S. maltophiliapresented high cell surface hydrophobicity (CSH), which kept within83.3%to95.6%from4h to72h under different pollutant systems. Then the CSH decreased withincreasing time. S. maltophilia made use of the additional carbon source, so changed thecell surface properties and regulated growth, thus, affecting the biodegradation of BaP. Ina single pollution system, BaP was open-loop decomposed in the conventional phthalatepathway. However, there was a new degradation pathway of BaP by S. maltophilia apartfrom the common phthalic degradation pathway in combined contamination system.The cell membrane permeability of S. maltophilia changed in the type and concentrationof pollutants. A single relatively high Cu²⁺content caused the permeability of cellmembrane continued to increase. But the BaP changed the plasma membrane permeabilityand split through "pore forming". Although the cell membrane changed in permeabilityafter treatment of pollutants, resulting in outflow of the cytoplasm, the cell wall still keptthe cell in original shape without complete splitting. However, after contact with thecombined pollutants for5day, the bacterial cells were out of shape seriously, theperiplasmic space enlarged, and the cytoplasm leaked. Furthermore, the nucleus brokedown and gradually disappeared, which reduced the cell activity and resulted in thegradual loss of S. maltophilia's ability to adsorb Cu²⁺.