Insights into the metabolic basis of the halotolerant Pseudomonas aeruginosa strain LVD-10 during toluene biodegradation

• Isolation of newly Pseudomonas aeruginosa strain LVD-10.
• Toluene biodegradation under extreme conditions reached more than 80% removal by LVD-10.
• Diesel biodegraded slightly higher in 30 g L−1 NaCl compared to 0 g L−1.
• The genes XylE1, 1,2-CTD, 2,3-CTD, rhlR1 and rhlR2 were detected in LVD-10.
• Expression gene levels encode enzymes of aromatic catabolism were not reduced in salinity 30 g L−1 NaCl.

In this work a Pseudomonas aeruginosa strain (LVD-10) has been isolated from activated sludge, based on its capability to biodegrade toluene under extreme conditions. In 0, 20 and 40 g L−1 NaCl the percentage of toluene removal reached 86%, 98% and 89% within 24 h, respectively. Interestingly, the removal of toluene occurred significantly faster compared to biomass growth, while the strain achieved 79.1% and 91.7% of 1 mL L−1 diesel removal after 7 days at 0 and 30 g L−1 NaCl, respectively. The pathways used by LVD-10 were determined through PCR amplification of genes that encode key enzymes involved in aromatics degradation and genes of the Quorum Sensing (QS) system. The genes XylE1, 1,2-CTD, 2,3-CTD, rhlR1 and rhlR2 were detected in LVD-10 whereas tbmD, TodC1 and Rmo were not found. The transcription level of genes measured by Q-PCR did not show any significant variation in gene expression of cells stimulated with salinity conditions of 30 g L−1 NaCl. However, when NaCl was increased to 50 g L−1 the genes were significantly down-regulated 48 h after toluene induction, while the expression of genes was restored to normal levels at 120 h. Furthermore, the expression of genes RhlI and RhlR2, which have been proposed to be involved in the Quorum Sensing (QS) system of P. aeruginosa, indicates that the strain has great ability to tolerate toxic environments as well as to perform efficient degradation of aromatic hydrocarbons.