Flow cytometric fingerprinting to assess the microbial community response to changing water quality and additives

Water is used for a very broad range of industrial applications with different water quality requirements. In all cases, the microbial water quality remains of importance as the microbial community can cause biofouling, microbial induced corrosion, odor problems, or health hazards. A close and accurate monitoring of the microbial water quality is therefore relevant for all water types used in industrial applications. Flow cytometry and additionally flow cytometric fingerprinting have been proposed before as methods to monitor the aquatic microbial communities but it remains unclear on how sensitive the fingerprinting method is for detecting quality changes in practice for different types of water. In this paper, we compared the microbial dynamics of coarsely filtered surface water, tap water, and demineralized water by challenging these waters with different concentrations and types of nutrients (C, N, and P) and additives such as corrosion inhibitors and biocides. We demonstrated that the cytometric fingerprints of the aquatic microbial communities differed in function of the type and concentration of product added, but that these differences are dependent on the type of water. Flow cytometry proved to be sensitive enough to detect subtle changes in microbial communities and to measure bacterial regrowth in different types of water. As a result, we conclude that cytometric fingerprints can be considered as indirect indicators of the physical–chemical composition of the water and a tool to monitor water biostability, as a tell-tale for minor environmental changes.