The Staining of Filamentous Fungi with Diazonium Blue B

The diazonium blue B staining reaction, commonly used to determine the subdivisional affinities of anamorphic yeasts, is adapted for staining cultures of filamentous fungi. When unprocessed mycelium from shake culture is treated with the reagent, Zygomycetes and some Basidiomycetes stain positively; Ascomycetes and most Basidiomycetes do not. After alkaline hydrolysis of the mycelium, Zygomycetes, Basidiomycetes, and some Ascomycetes react positively. Strains reacting negatively are exclusively ascomycetous. Apart from the standard positive and negative reactions, two anomalous reactions occur. The first is a bright yellow reaction found in certain Basidiomycetes; the second is a red reaction of the conidial slime of Hainesia lythri, a species with ascomycetous affinities.