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 risks to water quality and public health. Although monitoring biofilm formation in DWDS is essential for mitigating the risk of waterborne disease infections, current approaches that analyze the properties of the effluent cannot differentiate between planktonic and biofilm-associated bacteria. Quorum sensing (QS) systems are microbial communication mechanisms that regulate gene expression based on population density and are known to be more active in biofilm-associated bacteria than in planktonic bacteria. We hypothesize that bacteria dispersed from biofilms in DWDS influence QS-related mRNA levels detected in tap water effluent. Using Pseudomonas aeruginosa PAO1, a common bacterium found in DWDS, 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 the lasI gene (i.e., RNA/DNA levels) in P. aeruginosa was systematically analyzed under various growth conditions. Our experiments confirmed that P. aeruginosa exhibits significantly higher lasI mRNA levels in biofilms compared to planktonic states. Additionally, we cultivated P. aeruginosa biofilms in flow channels and demonstrated that lasI mRNA levels in the effluent correlate with biofilm growth conditions within the flow channels. These findings indicate that biofilm growth in DWDS can be investigated non-invasively and accurately by analyzing lasI mRNA in the effluent. This rapid, non-invasive, and accurate biofilm monitoring approach has the potential to enable large-scale inspections and routine monitoring of biofilm growth within DWDS, ultimately improving public health.