Charge-specific impacts of polystyrene nanoplastics on acidogenesis and biofilm adaptation in Ethanoligenens harbinense

Despite increasing awareness of the risks posed by nanoplastics (NPs) to environmental microbes, the charge-specific effects of functionalized NPs on anaerobic acidogenic bacteria remain poorly understood. This study investigated the impact of functionalized polystyrene (PS) NPs on Ethanoligenens harbinense, a model hydrogen-producing anaerobe. The growth, metabolic, and transcriptomic responses of this bacterium to non-functionalized (PS-NPs), amino-modified (PS-NH₂), and carboxyl-modified (PS-COOH) variants were examined. Compared with the control group without NPs addition, PS-NH₂ exerted the strongest inhibition, reducing hydrogen and ethanol production by 16 % and 20 %, respectively, while elevating reactive oxygen species (ROS) level by 148 %. It also decreased biomass and down-regulated the expression of ribosome- and translation-related genes. In parallel, biofilm adaptation resulted in an 12 % increase in polysaccharide. PS-COOH enhanced biofilm reinforcement with a 21 % increase in polysaccharides and up-regulation of bapA and membrane transporter-related genes. Overall, PS-NH₂ induced broad transcriptional changes, particularly in pathways related to the phosphotransferase system (PTS), ATP-binding cassette (ABC) transporters, genetic information processing, and signaling/regulatory systems in E. harbinense. These findings provide new insights into how surface charge modifications of NPs affect anaerobic bacterial metabolism and underscore their potential environmental risks.