A fluorescence staining method for the examination of microorganisms on natural substrates.

A fluorescence staining technique is described which uses the magnesium salt of 1-anilino-8-naphthalene sulfonic acid as a protein stain. At a concentration of 2.5 or 3.0 mg ml-1 in distilled water or phosphate buffer the compound does not fluoresce under ultra-violet or far blue illumination until it is bound to a protein or similar compound. It can be applied to natural substrates such as soil, food materials, organic material in water, etc., and can be examined immediately without any washing procedures. The application of this staining method to detect microorganisms on dead green algae (detritus) is described.