Acclimation Time Enhances Adaptation of Heterotrophic Nitrifying-Aerobic Denitrifying Microflora to Linear Anionic Surfactant Stress

Linear anionic surfactants (LAS) pose significant stress to microbial denitrification in wastewater treatment. This study investigated the performance and adaptation mechanisms of heterotrophic nitrification-aerobic denitrification (HN-AD) microbial consortia under LAS exposure after short-term (SCM, 2 months) and long-term (LCM, 6 months) acclimation. Results showed a dose-dependent inhibition of total nitrogen (TN) removal, with LCM achieving 97.40% TN removal under 300 mg/L LAS, which was 16.89% higher than SCM. Biochemical assays indicated that LCM exhibited lower reactive oxygen species (ROS) levels, a higher ATP content, and reduced LDH release, suggesting enhanced oxidative stress resistance and membrane stability. EPS secretion also increased in LCM, contributing to environmental tolerance. Metagenomic analysis revealed that long-term acclimation enriched key genera including <i>Pseudomonas</i>, <i>Aeromonas</i>, and <i>Stutzerimonas</i>, which maintained higher expression of denitrification (e.g., <i>nosZ</i>, <i>nirS</i>) and ammonium assimilation genes (<i>glnA</i>, <i>gltB</i>). Although high LAS concentrations reduced overall community diversity and led to convergence between SCM and LCM structures, LCM retained greater functional capacity and stress resistance. These findings underscore the importance of acclimation in sustaining denitrification performance under surfactant pressure and offer valuable insights for engineering robust microbial consortia in complex wastewater environments.