Crosstalk with Chlorella sp. reshapes the environmental fates of aspartame: From stress responses to contaminant destabilization

Aspartame (APM) is demonstrated to facilitate the dissemination of antibiotic resistance genes and react with residual chlorine in tap water to form cytotoxic disinfection byproducts, indicating potential ecological risks. However, it remains unclear whether microalgae, as primary producers and bioindicators, interact with APM and its transformation products (APM-TPs), or whether microalgae modify their environmental fates, thereby reshaping APM-associated risks. Here, we found that APM inhibited the growth of Chlorella sp. in a concentration-dependent manner (growth inhibition rate:16.6 % to 24.4 %), altered the composition of photosynthetic pigments, and induced oxidative damage. Spiking experiments of APM-TPs confirmed (2S,5S) 5-Benzyl-3,6-dioxo-2-piperazineacetic acid ((2S,5S)-DKP) as the primary inducer of oxidative stress in Chlorella sp. Targeted and non-targeted high-resolution mass spectrometry elucidated transformation pathways of APM under hydrolytic, photolytic, and Chlorella sp. conditions. Meanwhile, the conversion of APM to (2S,5S)-DKP was 75.6 %-97.0 % in water samples from the Yangtze River, Yellow River, and Ganjiang River, further elucidating the environmental fates of APM in natural water system. Notably, the first evidence of Chlorella sp.-catalyzed isomerization of (2S,5S)-DKP, with an isomerization rate of 46.7 %, was demonstrated. Finally, transcriptomics revealed mechanisms of APM-induced oxidative stress, photosynthetic impairment, and energy metabolism dysregulation in Chlorella sp. This study comprehensively elucidated the interaction mechanisms between APM and Chlorella sp., providing novel insights into the environmental geochemical behaviors of APM and (2S,5S)-DKP.