The LuxI/LuxR-Type Quorum Sensing System Regulates Degradation of Polycyclic Aromatic Hydrocarbons via Two Mechanisms

Members of the are renowned for their ability to degrade polycyclic aromatic hydrocarbons (PAHs). However, little is known about the regulatory mechanisms of the degradative pathway. Using cross-feeding bioassay, a functional LuxI/LuxR-type acyl-homoserine lactone (AHL)-mediated quorum sensing (QS) system was identified from PQ-2, a member of the order . Inactivation of the QS system resulted in a significant decrease in PAHs degradation. The QS system positively controlled the expression of three PAH-degrading genes ( , and ) and a regulatory gene , which are located on the large plasmid. Interestingly, the transcription levels of these three PAH-degrading genes were significantly down-regulated in the mutant. In addition, bacterial cell surface hydrophobicity and cell morphology were altered in the QS-deficient mutant. Therefore, the QS system in strain PQ-2 positively regulates PAH degradation via two mechanisms: (i) by induction of PAH-degrading genes directly and/or indirectly; and (ii) by an increase of bacterial cell surface hydrophobicity. The findings of this study improve our understanding of how the QS system influences the degradation of PAHs, therefore facilitating the development of new strategies for the bioremediation of PAHs.