2,4-Bisphenol S triggers physiological changes, oxidative stress and lipidome alterations in Gram-positive Enterococcus faecalis at environmental concentrations

2,4-bisphenol S (2,4-BPS) was an emerging BPS analogue as color developers, widely found in the environment. Fish toxicities, cytotoxicity and antiestrogenic effects of 2,4-BPS have been documented at mg L^-1, while the toxicity of 2,4-BPS at environmental concentrations (from ng L^-1 to μg L^-1) were scarce. Bacteria are identified as important components of the ecosystem, while little is known regarding the ecotoxicity of 2,4-BPS on bacteria. Enterococcus faecalis, a good indicator of faecal contamination and anthropogenic pollution, was exposed to 0.5-50 nmol L^-1 2,4-BPS. 2,4-BPS resulted in significantly decreased growth but notably increased membrane permeability in E. faecalis compared with the control. Hormetic effects on the expression of genes involved in DNA replication and efflux were observed. Inhibition of biofilm formation and induction of oxidative stress were caused by 0.5, 5 and 50 nmol L^-1 2,4-BPS. Fatty acyls, glycerolipids and glycerophospholipids were differentially regulated by 2,4-BPS. Glycerolipid metabolism and glycine, serine and threonine metabolism were significantly altered by 0.5 nmol L^-1 2,4-BPS, compared with glycerophospholipid metabolism disturbed by 5 and 50 nmol L^-1 2,4-BPS, showing concentration-dependent responses. Trend analysis of differential lipids demonstrated that there were three significant clusters, all of which were enriched in glycerophospholipid metabolism. 2,4-BPS elicited the strongest lipidomic responses at 5 nmol L^-1. Our study provides evidence for 2,4-BPS-induced toxicity to E. faecalis at environmental concentrations and contributes to a comprehensive understanding of the interaction between 2,4-BPS and Gram-positive bacteria.