Effect of fluorochromes on bacterial surface properties and interaction with granular media

Simple, efficient, and safe tagging methods are desired in short-term microbial transport studies such as in the study of filtration systems for water and wastewater treatment. Suitability of selected fluorochromes as bacterial tagging agents in transport studies was evaluated on the basis of stability of stained cells and the effect of staining on bacterial surface characteristics and interaction with granular media. Surface properties were characterized by zeta potential and microbial adhesion to hydrocarbons. The effect of staining on interactions between bacteria and porous media was evaluated in terms of removal of bacteria in batch adsorption tests using sand coated with aluminum hydroxide to enhance adsorption. The DNA-specific fluorochrome 4',6-diamidino-2-phenylindole (DAPI) had generally negligible effects on bacterial surface properties and interaction with sand, as indicated in batch adsorption tests using pure cultures (Escherichia coli or Acinetobacter sp.) and wastewater bacteria. Cells stained with DAPI were stable for 48 h at 4 or 20 degrees C. Other nucleic acid fluorochromes tested had different but significant effects on bacterial cells and produced less stable fluorescence. Since transport through porous media is modulated by surface properties, it may be concluded based on these results that the choice of fluorochromes is critical in microbial transport studies. DAPI appeared to be a promising tagging agent. Time dependence of fluorescence of stained cells may limit the use of fluorochrome-tagged cells in long-term transport studies.