Response of heterotrophic nitrification-aerobic denitrification bacterium Pseudomonas aeruginosa P-1 to Cd2+ and Pb2+ on ammonium removal performance, physiology, and transcriptome analysis

We investigated the response of Pseudomonas aeruginosa P-1, especially when performing heterotrophic nitrification-aerobic denitrification, to Cd2+ and Pb2+ stress. Ammonium removal performance, electron transport system activity (ETSA), and cell morphology were evaluated. The results showed that Pseudomonas aeruginosa P-1 could efficiently remove ammonium at concentrations of 50–200 mg L−1 of Cd2+ and Pb2+. The ETSA maintained a high value at 100 mg L−1 of Cd2+ and Pb2+, and it was less inhibited by Pb2+ than by Cd2+. The results of scanning and transmission electron microscopy showed that most cells had relatively intact surface at 100 mg L−1 of Cd2+ or Pb2+. RNA-Seq transcriptome analysis was employed to identify the mechanisms and key genes involved in the response of P. aeruginosa P-1 to Cd2+ and Pb2+ stress. The results showed that these differentially expressed genes involved in two-component systems and membrane transporters were upregulated. Therefore, P. aeruginosa P-1 may respond to Cd2+ and Pb2+ stress by regulating signal transduction to enable adaption to environmental changes and by varying membrane transporters of the cell membrane to control metal ion access. These findings are of importance in understanding the response mechanism of heterotrophic nitrification-aerobic denitrification bacteria to heavy metals and the potential application of these strains in practical wastewater treatment.