Disinfectant-driven selective gene expression and metabolic evolution: Unstable nitrite accumulation and enhanced...

The mixotrophic partial denitrification/anammox (MPDA) was a highly efficient nitrogen removal system, but its total nitrogen removal efficiency decreased from 95 % to 83 % due to nitrite supply destabilization under the pressure of disinfectants. The decrease in sulfur autotrophic denitrification activity and increase in heterotrophic denitrification activity were responsible for the partial denitrification (PD) disruption. Consistently, there was an increase in the abundance of Thauera, a decrease in Thiobacillus and Thiothrix. Following disinfectants exposure, the content of protein (as the redox mediator) from extracellular polymeric substances elevated, while the polysaccharide (as the carbon source) decreased. The abundance of nitrogen metabolism-related genes in anaerobic ammonium oxidation bacteria was generally elevated, supporting its carbon fixation and high activity in disinfectant-rich environments. The up-regulation of key genes in Embden-Meyerhof-Parnas pathway and tricarboxylic acid cycle, helped system to resist disinfectants, maintain nitrogen removal activity and accelerate electron production while disrupting PD. The disinfectants induced the up-regulation of antibiotic resistance genes (ARGs). Bacterial virulence factors (VFs) were weakened in Defensive VFs but enhanced in Offensive VFs. As a major contributor to VFs and ARGs, Candidatus Kuenenia was recognized as a health issue to the public.