Exploring gut microbiota responses to low-dose thallium exposure via food chain transfer: insights from soil-plant-human systems.

Thallium (Tl) is a toxic metal and priority pollutant, its soluble Tl levels in soil drive Tl accumulation in edible plants, posing health risks to gut microbiota via dietary exposure even at low doses. This study investigated Tl accumulation in sweet potatoes (4.45-32.87 µg/kg dry weight, 0.2442-1.7368 µg/kg wet weight) from soils (282.89-699.50 µg/kg) and its impact on a single pooled microbial community derived from fecal samples of three healthy adults (2 females, 1 male, 20-30 years) using an in vitro digestion-colon fermentation model. Low-dose Tl exposure drove significant, dose- and time-dependent genus-level restructuring of the pooled microbial community (Kruskal-Wallis, P = 0.001; PERMANOVA, P = 0.001, R2 = 0.783-0.980), without altering phylum-level alpha diversity (Kruskal-Wallis, P > 0.05), indicating compositional shifts rather than richness loss. Genus-level shifts included proliferation of harmful taxa (Escherichia_Shigella, Enterococcus) and reduction of beneficial taxa (Bacteroides, Prevotella, Akkermansia, Bifidobacterium, Blautia). Significant correlations (p < 0.05, 0.6883 < R2 < 0.9850) linked Tl content to Bacteroides, Prevotella, Escherichia_Shigella, and Enterococcus abundances. These findings demonstrate exposure-relevant microbiome shifts within this single pooled microbial community even at Tl concentrations below regulatory limits (300 µg/kg) via food chain transfer. However, as this in vitro model lacks host-microbe interactions (e.g., immune signaling, peristalsis) and the results reflect the response of one mixed inoculum from three donors rather than inter-individual variability, chronic in vivo studies are essential to validate these shifts and their metabolic and immune implications, informing soil-plant-human safety and public health strategies for low-dose dietary Tl exposure.