Evaluation of quorum sensing-related mRNA in tap effluent as a biomarker for biofilm dispersal in drinking water distribution systems

Biofilm growth and dispersion in drinking water distribution systems (DWDS) pose significant risks to water quality and public health. Although monitoring biofilm dispersion in DWDS is essential for mitigating the risk of waterborne diseases, current approaches that analyze effluent properties cannot distinguish between bacteria dispersed from biofilms and planktonic bacteria originating from the source water. Quorum sensing (QS) systems—microbial communication mechanisms that regulate gene expression based on population density—are known to be more active in biofilm-associated bacteria than in planktonic cells. We hypothesize that bacteria dispersed from biofilms in DWDS influence QS-related mRNA levels in tap water effluent. Using Pseudomonas aeruginosa , a common DWDS bacterium, as a model organism, we examined the transcription of the lasI gene, a key component of the las QS system responsible for synthesizing QS signaling molecules. Specifically, the transcriptional activity of lasI was found to be especially elevated at the biofilm surface, where dispersion primarily occurs. Additionally, we quantified lasI mRNA in tap effluent under two conditions known to trigger biofilm dispersion: extended stagnation time and transitions to oligotrophic water quality. These experiments support that the QS-related mRNA in the tap effluent serves as a biomarker of biofilm dispersion within DWDS.