Principles for quorum sensing-based exogeneous denitrifier enhancement of nitrogen removal in biofilm: a review

Denitrifying bacteria play critical roles in enhancing biological biofilm denitrification for nitrogen removal in industrial and municipal wastewater treatment and groundwater remediation. Evidence intensively confirms that exogenous quorum sensing (QS) bacteria prompt biofilm formation and denitrification. Yet, exogenous bacteria forfeiting during bioaugmentation may occur despite of its priority effect and improved community function, because of open, intricate traits in wastewater treatment system. Critical topics include regulating signal-based microecological structure, effectively assembling 3D biofilm, and regulating carbon and nitrogen metabolization of denitrifiers to reduce CO2 and N2O emissions. This review demonstrates classifications of denitrifiers and the vital role of QS in regulating biofilm denitrification. Furthermore, the ecological principles of microbial community construction with the addition of exogenous denitrifiers are summarized. Moreover, the effects of signaling molecules on carbon and nitrogen transcription and metabolization are discussed. In conclusion, technologies based on quorum sensing for enhanced denitrification have high application potential and challenges. Herein, we provide a guideline for enhancing nitrogen removal by exogenous quorum-sensing bacteria and synthetic biofilms design during upgrading of municipal wastewater treatment plants.