The Interaction Mechanism Of Stenotrophomonas Maltophilia Cells And Benzo [a] Pyrene – Copper Combined Pollutant On The Cellular Interface

To illuminate the characteristics and mechanisms involved in benzo[a]pyrene(Ba P) biodegradation and copper(Cu2+) biosorption in the polluted environment where Ba P and Cu2+ co-existed, this study has focused on the bio-treatment of Ba P and Cu2+ in various combinations by Stenotrophomonas maltophilia, which was isolated from the sediments of the e-waste contamination. The experimental biodegradation of Ba P and biosorption of Cu2+ were carried out in single and combined pollution system simultaneously to discusse the properties and metabolic pathways of Ba P/Cu2+ biodegradation/ biosorption on the microbial cell interface. The cellular stress response to Ba P and Cu2+ and the changes of cell properties were also investigated to determine the characteristics and mechanisms of co-contamination bioremediation. The results indicated that Ba P and Cu2+ were rapidly removed by S. maltophilia on the 1st d, but only less than 10 % Ba P being broken down due to temporary store in cells, instead of being decomposed immediately, and only 60 % of the removed Ba P was decomposed finally. However, the Cu2+ migration in different pollution systems changed regularly over time. From the 4th h on, the concentration of Cu2+ in extracellular solution declined rapidly, while the Cu2+ content inside cells continually increased. Stripping the cell walls of S. maltophilia was beneficial to the transportation of Ba P, but was detrimental to Cu2+ adsorption because many effective adsorption sites, such as carboxyl and phosphoryl were lost. There was more than one mechanisms of removal of Cu2+ by S. maltophilia, and when the pollutants types and environmental conditions changed will lead to different adsorption process of Cu2+. Normally, the bacteria removed Cu2+ through physical / chemical interaction at first, then, the Cu2+ combined with the active groups on the cell surface and took place oxidation-reduction reaction, which led to a part of Cu2+ changed into Cu+ and Cu. At the same time, the other part of Cu2+ adsorbed transported into bacterial cell across membrane by the P-type ATPase. However, when the cell activity was restrained, the S. maltophilia still can remove the Cu2+ in the solution through electrostatic interaction and extracellular precipitation. Especially, in the Ba P-Cu2+ combined pollutant system, most of Cu2+ was removed with the EPS by extracellular precipitation. Because of the pollutants, it appeared cell apoptosis, the intracellular ATPase activity, cell microstructure and cell membrane system were changed and damaged in a varying degree, thus, affecting the transport and removal of Ba P and Cu2+. The experiment results of 2-D and MALDI-TOF-TOF mass spectrometry showed that the differentially expressed protein spots were mainly related to the transport of Ba P, the oxidation-reduction reaction and the phosphorylation during biodegradation / biosorption of Ba P / Cu2+ by S. maltophilia.