Research progress in bioreduction mechanisms for hexavalent chromium and environmental implications

Hexavalent chromium [Cr(VI)] is a widespread and highly toxic heavy metal contaminant commonly found in industrial effluents from electroplating, metallurgy, and dye manufacturing. Due to its strong oxidizing nature, high solubility, and severe biological toxicity, Cr(VI) is recognized as a priority contaminant to be managed in aquatic and terrestrial environments. Although conventional treatment technologies can rapidly reduce Cr(VI) concentrations, they often entail high costs, pose risks of secondary pollution, and are susceptible to environmental fluctuations. Bioreduction of Cr(VI) has emerged as a promising alternative, offering advantages such as low energy requirements, environmental compatibility, and operational sustainability. This review provides a comprehensive overview of the core mechanisms underlying Cr(VI) bioreduction, which involve key chromate reductases, intracellular and extracellular electron transfer pathways, gene regulatory networks, and adaptive strategies of microbial communities under stress. Furthermore, we discuss the synergistic contributions of metabolic pathways, such as denitrification and sulfur cycling, to elucidate electron competition and pathway modulation in complex multi-contaminant systems. Subsequently, we analyze the effects of environmental parameters including pH, temperature, Cr concentration, and electron donor types on bioreduction efficiency. Representative studies are discussed to illustrate detoxification performance, community succession, and ecological restoration outcomes under field conditions. Finally, this review envisions future advances in microbial remediation through the application of synthetic biology to construct engineered microbial strains, the use of multi-omics technologies to elucidate metabolic pathways, and the integration of artificial intelligence (AI) with in situ sensing technologies for dynamic regulation. It further outlines a developmental framework centered on “intelligent detection-adaptive response-multifunctional coordination”, providing both a theoretical foundation and technological guidance for the in situ remediation of Cr(VI) contamination.