Perfluorohexane sulfonate (PFHxS)-induced energy metabolism disruption in Chlorella pyrenoidosa: Integrating physiological and transcriptomic insights.

Perfluorohexane sulfonate (PFHxS), a widely used alternative to perfluorooctane sulfonate (PFOS), has been prevalent in aquatic environments. However, its toxic mechanisms in algae remain poorly understood. In this study, a 12-day exposure experiment was conducted to systematically investigate the toxicity of PFHxS in Chlorella pyrenoidosa through physiological parameter measurements and transcriptomic analysis. The results revealed that significant growth inhibition (9%) was observed at 1 mg/L PFHxS on day 12, accompanied by altered photosynthetic responses, including decreases in chlorophyll a and carotenoid contents by 11% and 15%, respectively, at the late exposure stage. On day 12, the accumulation of reactive oxygen species (ROS) triggered a compensatory upregulation of antioxidant enzyme activities, with superoxide dismutase (SOD) and catalase (CAT) increasing by 74% and 79%, respectively. This response was insufficient to prevent severe oxidative stress, which resulted in lipid peroxidation and substantial impairment of energy metabolism, marked by a 57% decline in adenosine triphosphate (ATP) and a 55% decline in reduced nicotinamide adenine dinucleotide phosphate (NADPH). Transcriptomic profiling suggested that PFHxS exposure was associated with suppression of the Calvin cycle and glycolysis while inhibiting the tricarboxylic acid (TCA) cycle and oxidative phosphorylation, thereby impairing energy synthesis. Although C. pyrenoidosa appeared to modulate energy metabolism and exhibited transcriptional changes associated with reduced glycogen turnover and altered fatty acid metabolism, severe oxidative damage coupled with impaired energy metabolism ultimately led to metabolic disturbance. This study provides evidence relevant to evaluating the ecological risks of PFHxS to aquatic systems and provides critical evidence for assessing the environmental impacts of PFHxS.