Microbial self-regulation and electron transport reconstruction under Cr(VI)-4-CP stress: From synergistic inhibition to antagonistic interaction.

Understanding how microbial communities adapt to multi-pollutant stress is crucial for efficient denitrification. Although previous studies reported the effects of heavy metals and phenolic compounds individually or in mixtures, the deep mechanisms by which combined stressors reshape microbial electron transport and community structure remain unclear. This study explored the denitrification response to combined Cr(VI) and 4-chlorophenol (4-CP) stress, revealing a temporal shift from synergistic inhibition (acute exposure) to antagonistic interaction (long-term adaptation). Acute Cr(VI)-4-CP exposure caused complete inhibition of denitrification within 18T, accompanied by the activation of dissimilatory nitrate reduction to ammonium. Cr(VI) intracellular accumulation (71.78 %) induced oxidative imbalance and 4-CP prioritized metabolism disrupted electron donor availability, collectively causing FMN decreasing, which decreased NAR electron capture efficiency. Prolonged exposure activated microbial self-regulation (denitrification efficiency recovered to 31.42 %), including extracellular Cr(III) immobilization (84.19 %), antioxidant enzyme upregulation, reshaping oxidative-antioxidant homeostasis. Concomitantly, the electron transport was remodeled via FMN/FAD complementarity, enabling partial recovery of NAR activity and suppression of N2O accumulation. Metagenomic analysis further identified functional cooperation among Microbacterium, Thermomonas, Diaphorobacter, and Acidovorax, supporting glucose/4-CP co-metabolism (COD4CP/CODglucose=1/1.26) and stabilized denitrification performance. This study established a mechanistic framework linking microbial self-regulation and electron transport remodeling, providing new insights into the resilience of denitrifiers under multi-pollutant stress.