Unveiling the synergistic regulation of Co-metabolic substrates and Fe(III) on tetrabromobisphenol A degradation by Geobacter sulfurreducens PCA.

Tetrabromobisphenol A (TBBPA) poses a significant environmental threat due to its persistence and toxicity. This study investigated the anaerobic degradation of TBBPA by Geobacter sulfurreducens PCA, focusing on the synergistic effects of co-metabolic substrates (glucose and humic acid) and Fe(III) sources (ferric citrate and ferrihydrite). Results demonstrated that both substrates significantly enhanced TBBPA degradation, with optimal doses of 4.0 g/L for glucose (83.31% degradation) and 0.4 g/L for humic acid (80.70% degradation). Kinetic analysis revealed that glucose primarily increased the affinity for TBBPA (lowering Km to 456.42 mg L-1), while humic acid boosted the maximum degradation capacity (increasing Vmax to 47.23 mg L-1·d-1). The addition of Fe(III) further accelerated degradation, with ferric citrate being more effective than ferrihydrite due to its higher solubility. At higher TBBPA concentrations (>100 mg/L) and Fe(III) loads, humic acid exhibited superior performance, leveraging its role as an electron shuttle. LC-MS analysis identified 12 intermediates, leading to the proposal of two novel degradation pathways: a reductive debromination-ring cleavage pathway (Pathway A) and an oxidative cleavage-debromination pathway (Pathway B). The discovery of Pathway B highlights the unique capability of G. sulfurreducens PCA to synergistically employ oxidative and reductive mechanisms. These findings provide profound insights into the microbial degradation of TBBPA and offer a strategic framework for optimizing bioremediation in anaerobic environments.