Accurate and non-invasive monitoring of biofilms in drinking water distribution systems through the analysis of quorum sensing-related mRNA in the effluent

Biofilm growth and dispersion in drinking water distribution systems (DWDS) pose significant risks to water quality and public health. Although monitoring biofilm formation 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 expression 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 systematically analyzed in both planktonic and biofilm-associated bacteria and was found to be especially elevated at the biofilm surface, where dispersion primarily occurs. Additionally, we quantified lasI mRNA in effluent under two conditions known to trigger biofilm dispersion: (1) low free chlorine levels combined with extended stagnation, and (2) transitions to oligotrophic water quality. These experiments support that biofilm growth and dispersion in DWDS can be accurately and non-invasively monitored by analyzing lasI mRNA in the effluent. This rapid, non-invasive approach offers potential for large-scale assessments and routine monitoring of biofilm dynamics in DWDS, ultimately contributing to improved public health.