Preliminary Study On Quorum Sensing System In Novosphingobium Pentaromativorans US6-1 For BaP Biodegradation

For a long time,polycyclic aromatic hydrocarbons(PAHs)pollution abatement has become the hot topic in environmental science.Bioremediation is considered to be the main way to remove PAHs in the environment because of its high degradation ability and friendly to environment.In recent years,people have made progress in screening efficient degradation bacteria and exploring the metabolism of PAHs.However,how the bacteria to contact with each other under the PAHs stress is still unclear.In this research,a Gram-negative bacterium,Novosphingobium pentaromativorans US6-1,which is capable of degrading 2-ring to 5-ring PAHs,was choosed to study the quorum sensing system and its function on intercellular information exchange in the process of PAHs degradation using microscopic observation and genome analysis.The main results are as follows:Firstly,a variety of bacterial stress response including cell shrinkage,aggregation and extracellular secretion were found in the process of benzopyrene degradation using transmission electron microscopy,scanning electron microscopy and fluorescence microscopy.Secondly,the AHLs signal molecules was detected in strain US6-1 by report plate.It was found that strain US6-1 increased biofilm formation during the BaP degradation process of 1 d.The ability to increase the performance of the biofilm thickness and roughness was measured using crystal violet staining and fluorescence microscopy.Meanwhile,the ability to increase the extracellular polysaccharide and protein further indicated that US6-1 started a variety of physiological response under the BaP stress.Three quorum sensing pathways were observed in US6-1 with the genome analysis.Real-time quantitative PCR results show that US6-1 has started three quorum sensing pathways in the process of BaP degradation.It was found that relative expression of gene JI59_RS07565 significantly correlated to the biofilm formation and EPS production(p<0.01 and p<0.05).The result indicated that AHLs-QS pathway palys the leading role.While the other two pathways coordinated with the formation of more rough biofilm and more EPS.In addition,several functions similar to LuxR solo protein were detected in US6-1.LuxR protein can receive signals from the two-component system to participate in the process of physiological regulation of US6-1 for degradation of BaP.In this research,the function of quorum sensing on the degradation of BaP was measured using quorum sensing inhibitor.It was found that 5 ?g/mL 4-nitropyridine-N-oxide(4-NPO)could significantly inhibit the production of AHLs without affecting the growth of the cells.The degradation rate of BaP decreased significantly when 4-NPO was added,which indicated that AHLs has effect on the degradation of BaP.The above results suggest that Novosphingobium pentaromativorans US6-1 started the QS system to control the formation of biofilm and EPS so that the strain enhanced the adsorption of PAHs and achieved PAHs degradation.The results of this study provide a basis for revealing the mechanism of US6-1 response to PAHs at the population level,and also give a theoretical basis for establishing the strategies of PAHs bioremediation in the future.