Distinct responses of Pseudomonas aeruginosa PAO1 exposed to different levels of polystyrene nanoplastics

Large amounts of discarded plastics in the environment can be aged into microplastics and nanoplastics, which are not easily removed, posing potential nonnegligible risks to the ecosystem and human health. Although previous studies have revealed that nanoplastics have detrimental impacts on microorganisms, the potential molecular mechanisms of nanoplastic particles' effect on microbial growth and metabolism are still lacking. Here, multiple responses of Pseudomonas aeruginosa PAO1 (PAO1) to different levels of polystyrene nanoplastics (PS NPs) exposure were investigated by physiological experiments, live/dead staining, redox status, and genome-wide RNA sequencing. The results showed that PS NPs had dual effects on PAO1, and different concentrations of PS NPs demonstrated different effects on the growth and metabolism of PAO1. All levels of PS NPs had no obvious biocidal effect on PAO1. The production and consumption of ROS were in dynamic equilibrium and could be regulated genetically to ensure that the ROS level was in the biotolerable range. 20 and 50 mg/L of PS NPs severely inhibited the nitrate reduction, while 0.1 mg/L of PS NPs promoted the denitrification and TCA cycle. Meanwhile, 20 and 50 mg/L of PS NPs resulted in intense down-regulation of genes involved in denitrification. In contrast, the expression of genes involved in respiration is promoted with generated energy to withstand stress from high-level PS NPs, coinciding with the physiological results. In addition, our results showed that PS NPs concentrations of 20 and 50 mg/L exposure substantially up-regulated the expression of genes encoding for flagellar biosynthesis and biofilm formation to tackle the stress. Our findings would provide new insights into the interactions between environmental bacteria and PS NPs at the transcriptional level, thereby enhancing our understanding of the potential risks of PS NPs to microbial ecosystems and public health.