Acyl homoserine lactone based quorum sensing affects phenanthrene removal by Novosphingobium pentaromativorans US6-1 through altering cell surface properties

Abstract

Novosphingobium pentaromativorans US6-1 can degrade polycyclic aromatic hydrocarbons (PAHs) and produce acyl-L-homoserine lactones (AHLs), which are quorum-sensing (QS) signal molecules. However, whether and how QS affects bioremediation of PAHs remain unknown. In this study, using novI and novR deletion mutants (ΔnovI and ΔnovR) and complementary strains (ΔnovI (pCM62-novI) and ΔnovR (pCM62-novR)), we proved that novI and novR constitute the QS system in US6-1. The expression of most genes encoding PAH degrading enzymes were significantly upregulated in mutants, and this finding was consistent with measurements showing that mutants had a higher phenanthrene (phe) removal efficiency (PRE) than wild-type US6-1 (WT_US6-1). Both mutants had significantly higher cell surface hydrophobicity (CSH) and lower extracellular-polysaccharide (EPS) production than WT_US6-1. The functional C–O–C groups on the cell membrane were also changed in mutants. Upregulation of spt in ΔnovI and downregulation of epsd in ΔnovR supported the measurement results of CSH and EPS production. These results indicate that the AHLs-based QS in US6-1 negatively regulates PRE and CSH and positively regulates EPS production. Correlation analysis indicates that in US6-1, QS negatively affects PRE by altering the cell surface properties, and hence, QS may serve as a target for controlling bioremediation.