Quantitative lipid biomarker detection of unculturable microbes and chlorine exposure in water distribution system biofilms

Biofilms in the drinking water distribution system can protect pathogens from disinfection and provide the inocula for periodic infestations. Assessing these biofilms can be difficult, as the plate counts of pelagic bacteria may bear little relationship to the biofilm load. Culturing the water at the outlet most often does not reflect the biofilm composition. Herein we show that analysis of polar lipid fatty acids recovered from biofilms on devices possessing a large surface area provides quantitative analysis of the viable biomass, community composition, and nutritional status that is independent of the recovery and culturability. Analysis of the polar lipid fatty acids indicated the biofilm contained a stressed and predominantly Gram-negative bacterial community. The composition was not significantly different whether collected in the summer or winter. Oxirane (epoxide) fatty acids were detected in the polar lipids of the biofilm, indicating exposure to chlorine and loss of viability within the biofilm. Tests with monocultures of Escherichia coli and Sphingomonas paucimobilis exposed to chlorine resulted in oxirane fatty acid generation and rendered them nonculturable.