Nile blue A for staining Escherichia coli in flow cytometer experiments

Nile blue A is used as a stain for polyhydroxyalkanoic acid-accumulating Microorganisms or to detect polyhydroxyalkanoic acids in Microorganisms. Here we show that Escherichia coli cells that do not accumulate detectable polyhydroxyalkanoic acids can be stained with Nile blue A and that this staining is sufficient for identifying these cells in fluorescence-activated cell sorting (FACS) experiments. Nile blue A staining did not affect either surface display of peptides or specific labeling of these peptides by a second fluorescence. Staining E. coli for flow cytometry using Nile blue A is an easy-to-handle and low-cost alternative to Other fluorescent dyes or the intracellular expression of, for example, green fluorescent protein.