Hydrolytic Dehalogenation of Toxic Haloacetic Acids via Carbon Metabolism Regulation during Microbial Denitrification

Microbial denitrification is essential in the nitrogen cycle to enhance the quality of the reclaimed water. In addition to nitrogen removal, it has the potential to control trace pollutants. However, the fates of toxic disinfection byproducts (DBPs) on denitrification remain unelucidated. The current study focused on <i>Paracoccus denitrificans</i> (<i>P. denitrificans</i>) to investigate the response mechanisms of denitrifying microorganisms to HAAs, one of the main categories of DBPs. Upon exposure to 20 μM monoiodoacetic acid (MIAA), the number of extracellular reactive oxygen species in <i>P. denitrificans</i> increased to 2.7 times at 16 h. Concurrently, the specific nitrate reduction rate dropped by 9.3% and the specific growth rate declined by 26.7%, leading to the slowdown of the denitrification process. Nevertheless, <i>P. denitrificans</i> increased the activity of the tricarboxylic acid cycle and electron transport for sustainable denitrification under MIAA stress. Microbial hydrolytic dehalogenation contributed to over 70.0% MIAA removal, and it led to the release of iodine ions. MIAA was detoxified and concerted into low-molecular-weight organic acids, which then participated in carbon metabolism. The removal efficiency of different toxic HAAs was also compared to evaluate the adaptiveness of the DBP control. This research highlighted the interactions between denitrifying microorganisms and DBPs, providing new insights into the ecological safety protection of high-quality reclaimed water.