Aspartame induces hormesis-toxicity switch in microalgal‑bacterial granular sludge: Community assembly and functional gene responses.

Based on the distribution of aspartame in anaerobic digestion effluent (ADE) from food waste, this study explored the potential application of microalgae-bacterial granular sludge (MBGS) for treating ADE containing aspartame. While previous studies have focused on toxicity, the core scientific question of this work is to elucidate the adaptive regulatory mechanisms that govern MBGS performance under varying aspartame stresses. Notably, MBGS exhibited broad adaptive tolerance to varying aspartame concentrations, displaying a typical hormetic response: low-level aspartame exposure exerted a stimulatory effect on MBGS performance, whereas high-level exposure triggered evident inhibitory impacts. At the low concentration level, MBGS assembled a multilayered stress-tolerant defense framework characterized by bioactive metabolites, extracellular polymeric substance barriers and oxidative stress modulation. Aspartame reshaped the community abundances of Cyanobacteriota and Pseudomonadota to establish a synergistic microbial community while upregulating the abundance of key genes involved in carbon, nitrogen and phosphorus cycles. In contrast, high-concentration aspartame induced severe oxidative stress that impaired the physiological defense capability of MBGS, and suppressed ATPase-mediated electron transfer and photosynthetic activity. Despite microbial compensatory regulation and metabolic reprogramming toward stress adaptation, the overall treatment efficiency of the system was markedly compromised. This study not only elucidates aspartame's environmental behavior and ecological risks but also provides a novel theoretical framework for leveraging the hormetic effect in MBGS-based treatment of artificial sweetener wastewater.