The Quorum Sensing Regulates The Degradation Of Polycyclic Aromatic Hydrocarbons In Croceicoccus Naphthovorans PQ-2

Polycyclic aromatic hydrocarbons(PAHs)are hydrocarbons containing more than two benzene rings.PAHs with four to six rings are carcinogenic,teratogenic,and mutagenic.They have a stable chemical structure and can exist in nature for a long time.The PAHs are harmful to human health and the ecological environment.Quorum sensing(QS)is an intercellular communication process that enables bacteria to change behaviors together.The applications of QS in biodegradation of PAHs are attractive.Although there are many studies on biochemical pathways of PAHs degradation,there are little about the regulatory mechanisms of degradation pathways.Croceicoccus naphthovorans PQ-2 belongs to the Erythrobacteraceae in the Sphingomonadales family.It can degrade PAHs and generate QS signals.However,it is not clear if QS can regulate PAHs degradation in strain PQ-2.In this study,the Lux I-Lux R type QS system was identified and the regulation of QS on PAHs degradation in strain PQ-2 was explored in strain PQ-2.First,the whole genome of strain PQ-2 was analyzed.It was found that strain PQ-2 has a functional acylated homoserine lactone(AHL)-mediated QS system.Then,lux I and lux R were deleted.The cross-feeding and transcription levels analysis confirmed that QS system in strain PQ-2 consists of AHL synthase Lux I and regulator Lux R.Next,the gene cluster for PAHs degradation on large plasmid P1 in strain PQ-2 was predicted,and the metabolites of PAHs were detected by GC-MS.It was found that PAHs degradation in strain PQ-2 is via phenanthrene degradation pathway.In addition,the further degradation of phenanthrene is via the salicylic acid pathway.Finally,the catechol was decomposed by meta-cleavage of catechol 2,3 dioxygenase.The removal of large plasmid P1 from strain PQ-2 indicated that P1 is crucial for PAHs degradation.Second,the degradation ability was assessed by detecting residual phenanthrene.It was found that the inactivation of the QS system caused a significant reduce of PAHs degradation ability in strain PQ-2.Compensation of QS can accordingly recover the PAHs degradation ability,indicating that the QS system regulates PAHs degradation.Further experiments showed that the QS system controls the expression of ard R encoding the aromatic degradation regulator,which in turn regulates the expression of several genes special for PAH-degradation located on the large plasmid P1.Finally,the adherence of cells to hydrocarbons was compared between wild type of PQ-2 and ?lux I.It was found that wild-type strain was twice as hydrophobic as the mutant strain,indicating that QS also had a large effect on cell hydrophobicity.Observation under electron microscopy showed that the surface of wild-type cell was rougher than the mutant.All these data indicated that the QS system can change the surface hydrophobicity of the cells,thereby affecting the cell's attachment to PAHs.These findings have improved our understanding of how QS systems affect the degradation of PAHs,which is important to the development of new strategies for PAHs bioremediation.