Biological response of protists Haematococcus lacustris and Euglena gracilis to conductive polymer poly (3,4‐ethylenedioxythiophene) polystyrene sulfonate

Improving the growth and pigment accumulation of microalgae by electrochemical approaches was considered a novel and promising method. In this research, we investigated the effect of conductive polymer poly (3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) dispersible in water on growth and pigment accumulation of Haematococcus lacustris and Euglena gracilis. The results revealed that effect of PEDOT:PSS was strongly cell‐dependent and each cell type has its own peculiar response. For H. lacustris, the cell density in the 50 mg·l−1 treatment group increased by 50·27%, and the astaxanthin yield in the 10 mg·l−1 treatment group increased by 37·08%. However, under the high concentrations of PEDOT:PSS treatment, cell growth was significantly inhibited, and meanwhile, the smaller and more active zoospores were observed, which reflected the changes in cell life cycle and growth mode. Cell growth of E. gracilis in all the PEDOT:PSS treatment groups were notably inhibited. Chlorophyll a content in E. gracilis decreased while chlorophyll b content increased in response to the PEDOT:PSS treatment. The results laid a foundation for further development of electrochemical methods to promote microalgae growth and explore the interactions between conductive polymers and microalgae cells. Significance and Impact of the Study: This study is unique in revealing the effects of conductive polymer PEDOT:PSS colloidally dispersed in water on the growth and pigment accumulation of freshwater microalgae for the first time. The effect was different on each microalgae species. PEDOT:PSS exhibited the hormesis effect on Haematococcus lacustris, promoting its growth at lower concentrations and inhibiting at higher concentrations. For Euglena gracilis, cell growth was significantly inhibited, which might be attributed to PEDOT:PSS impeding the photosynthesis. Our work provides a foundation for future studies addressed to investigate its aquatic ecotoxicity, mechanism of the effect, and interactions between microalgal cells and conductive polymers.