Genetically engineered microbes: A novel bidirectional regulator for biofilm in combatting aquatic nitrogen pollution

Exogenously adding N-acyl homoserine lactones (AHLs) can enhance the performance of wastewater biofilm, but their cost limits their use. In this study, four genetically engineered microbes (GEMs), including two quorum sensing (QS) GEMs (luxL and luxM) and two quorum quenching (QQ) GEMs (aiiA and aiiO), were constructed through genetic recombination technology. Sequential batch biofilm reactors (SBBR) were employed to evaluate their bidirectional regulatory effects on biofilm formation. QS-GEMs could secrete various AHLs, increasing the biofilm formation index (BFI) amount by 42.4-171.5 %. Conversely, QQ-GEMs could degrade AHLs, reducing biofilm formation index amount by 45.8-65.6 %, thus limiting and balancing biofilm and QS mechanisms. QS-GEMs enhanced gene expression key to biofilm formation (algI and bapA), denitrification (NosZ, NirS and NapA), and AHLs synthesis (lasI, rpfF and rpfB), improving biofilm thickness and nitrogen pollutant removal, reducing start-up time by 42.85 %. In comparison with AHLs, QS - engineered bacteria not only exhibited a more persistent and stable biofilm - strengthening effect but also were able to delay biofilm aging. Preliminary environmental risk assessment of GEMs suggested manageable risks, but further investigation under real aquatic ecosystem conditions is necessary to substantiate their safety. This study presented a novel solution for replacing traditional exogenous AHLs methods and enhancing biofilm denitrification.