Single-Cell Bacterial Bioreporter Assays to Measure Hydrocarbons

Abstract

Assays based on bacterial bioreporters can efficiently detect hydrocarbons in aqueous samples. The bioreporter cell, which is genetically engineered to respond to a specific stimulus via quantifiable output, acts as an individual sensor. Although reporter assays most often integrate a signal coming from an entire population of reporter cells, certain techniques allow us to extract information at the single-cell level and permit us to investigate individual variation in a population of cells. Here, we describe how to use epifluorescence microscopy to measure single-cell response in bacteria expressing autofluorescent proteins. In the assay, the reporter bacteria are directly (in aqueous phase) or indirectly (via the gas phase) exposed to hydrocarbons in a glass vial. After a given incubation period, a sample of the bioreporter population is transferred to a coated glass slide for microscopy analysis, and microscope images are used to further quantify the fluorescence intensity in individual bacteria. The response of the bioreporter cells can then be measured in hydrocarbon-contaminated samples and compared to hydrocarbon standards.