Involvement of quorum sensing genes in biofilm development and degradation of polycyclic aromatic hydrocarbons by a marine bacterium Pseudomonas aeruginosa N6P6

Abstract

Biofilm-forming and acyl homoserine lactone (AHL) synthase-positive Pseudomonas aeruginosa N6P6 was isolated from seawater after selective enrichment with two polycyclic aromatic hydrocarbons (PAHs), viz. phenanthrene and pyrene. AHL synthesis was detected qualitatively using bioreporter strains. This marine bacterium putatively synthesized N-(3-oxododecanoyl)-L-homoserine lactone and N-butyryl-L-homoserine lactone, which were identified by TLC, GC-MS, and HPLC. Two quorum sensing (QS) genes coding for AHL synthase, i.e., lasI and rhlI, were identified in the bacterium. lasI and rhlI gene expression was studied during biofilm mode of growth at different phases using quantitative real-time PCR (qRT-PCR). The expression of lasI increased with increase in biofilm growth. In contrast, the expression of rhlI decreased during log phase of biofilm growth. The changes in lasI/rhlI expression level had significant effects (P<0.05) on biofilm architecture and subsequent PAH degradation rate. Degradation of phenanthrene and pyrene by P. aeruginosa N6P6 was affected by biofilm growth and lasI expression. The respective phenanthrene degradation for 15, 24, 48, and 72 h old biofilm after 7 days was 21.5, 54.2, 85.6, and 85.7%. However, the corresponding pyrene degradation was 15, 18.28, 47.56, and 46.48%, respectively, after 7 days. A significant positive correlation (P<0.05) was observed between lasI expression and PAHs degradation. However, in the presence of tannic acid, a QS inhibitor (QSI), PAHs degradation, biofilm formation, and pyocyanin production reduced significantly which confirmed the pivotal role of QS in biodegradation of PAHs. The findings suggest that AHLs play a pivotal role during biofilm development and subsequent bioremediation of PAHs.

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“…Both AHL QS systems are known to be activated immediately after biofilm development has begun, reaching a peak at 48 h when a certain thickness of the biofilm has been achieved. Subsequently, QS gene expression decreases (De Kievit et al, 2001;Mangwani et al, 2015). It is assumed that after 48 h, the concentration of QS molecules is higher than that after 24 h due to the growth and biofilm formation of Pa over time.…”

Bacterial biofilms and quorum sensing: fidelity in bioremediation technology

“…PAH degradation by a marine bacterium P. aeruginosa N6P6 was significantly increased with the increase in QS genes (lasI and rhlI) expression. Increase in QS gene expression enhances the biofilm growth and EPS production resulting in augmented degradation of PAH (Mangwani, Kumari, & Das, 2015). QS-induced emulsifier production by bacteria helps in dispersing oil and allows bacteria to grow by providing greater surface area.…”

Recent Advances in the Study of Marine Microbial Biofilm: From the Involvement of Quorum Sensing in Its Production up to Biotechnological Application of the Polysaccharide Fractions

“…Indeed, the expression of rhlI decreased during the log phase of biofilm growth, while the expression of lasI increased with the increase in biofilm growth. This difference in the lasI and rhlI genes' expression significantly affected the biofilm architecture and PAH degradation rate, as well [71].…”