Aromatic hydrocarbon exposure alters soil microbial communities and redox-driven carbon metabolism

The environmental behavior and toxicological impacts of benzene, toluene, ethylbenzene, and xylene (BTEX) have been widely studied. Yet their concentration-dependent effects on soil microbial structure, redox dynamics, and metabolism remain insufficiently understood, constraining predictions of ecosystem responses and the development of targeted bioremediation strategies. Here, we explored how exposure to different concentrations of BTEX reshaped microbial community structure and metabolic function by integrating phased amplicon sequencing, metagenomic analysis, and metabolite profiling. BTEX exposure did not significantly alter the overall microbial richness or diversity across treatment groups but substantially changed the taxonomic composition (Stress = 0.096, R = 0.2284, P = 0.0500). It reduced the dominance of Bacillus and enriched various Clostridium spp. closely associated with acetate and butyrate production. At higher BTEX concentrations, Sporolactobacillus was selectively enriched, directing carbon flow toward lactate production. Functionally, BTEX inhibited early reactions in the pentose phosphate pathway (PPP), while increasing the abundance of genes involved in downstream glycolysis and PPP, leading to rapid pyruvate and NADH accumulation. Meanwhile, inhibition of NADH: ubiquinone oxidoreductase indicated a reduced capacity for respiratory NADH turnover. At slight BTEX concentrations, the redox imbalance increased NADH availability, thereby enhancing alcohol synthesis by 38.03 % (±29.18 %) (P < 0.05). Conversely, high BTEX concentrations enhanced lactate biosynthesis, redirecting carbon and reducing equivalents away from alcohol and acid accumulation (P < 0.05). These findings demonstrate that BTEX reshapes microbial redox dynamics and carbon allocation in a concentration-specific manner, providing mechanistic insights into soil microbiome responses to aromatic hydrocarbon pollution and a basis for designing and optimizing future bioremediation strategies.