Results: 1. Fluorochromes Calcofluor white M2 R new: This well-known fluorochrome is widely used as and optical brightener. It stains 1,4-linked polymers (cellulose, chitin) and thus hyphal and cell walls (SENGBUSCH 1983; DOLAN & McNICOL 1986). GULL & TRINCI (1974) used it to stain the walls in the apical region of growing hyphae; but old structures which are still active but no longer metabolizing intensively are also visible due to the staining of hyphal walls. An additional advantage of calcofluor W is its stability of the fluorescence as well as its binding to the polymers: even permanent mounts exhibited the fluorescence after long times. Fig. 1 shows the fluorescence of calcofluor W in Arthrobotrys oligospora. The substance was obtained from Sigma (F-6259). It was applied by mixing 50 mg calcofluor white to 5 ml buffer solution (Tris-buffer pH 9.00) as a stock solution. The working solution was obtained by dilution 100 µl stock solution to 9.9 ml buffer. This working solution was quite stable. Fig. 1: Arthrobotrys oligospora: Mycelium with capture organs and a captured nematode - marked by the assimilative hyphae - stained with calcofluor white. Bar represents 100 µm. Rhodamin B: This is a well-known stain for lipid substances (GRIFITH 1984; PEARCE 1984; HEATH 1988). During these experiments it could be used only after fixation by heat or ethanol; the results, however, were not satisfactory. As a vital stain it could be used only in combinations with other fluorochromes as shown above. In these cases it gave better results with assimilative hyphae inside the nematode corpses and allowed differentiation of conidia, which exhibited a yellowish-red fluorescence. Further fluorochromes: The following substances were tested, but did not give satisfactory results with predacious fungi. Their application, however, might be useful with other investigations. Acridinorange: A well-known vital stain, which gave in our studies good results with bacteria only. DAPI (41-6-diamino-2-phenyl indole): Widely used for fluorochroming of nuclei (RAJU 1982); in soil, however, the results were quite bad. Ethidium bromide: Without fixation by ethanol bacteria were stained exclusively; in soil it did not yield good results. Combinations: To get all fungal - or hyphal - structures stained, FDA fluorochromation was often completed by the addition of calcofluor W. Though the pH optima were in both cases different (pH 6.0 for FDA and 9.0 for calcofluor white), an overlapping region was found at pH 7.0. Since, in addition, the Pleomopak 2.4 equipment allowed the changing of the filter units on a revolver, differentiated observations with both the stains separately could be done simultaneously. Double exposures allowed the documentation of the entire information, as shown in Fig. 2 and 3. In some cases the treatment was completed by addition of rhodamin B, which allowed a further improvement of the picture. Its role in the fluorochroming of living i. e. active fungi is not clear, as this substance demands previous fixation - which was not possible with FDA-staining. Fig. 4 shows the result of such a triple staining with FDA, calcofluor white and rhodamin B. Fig. 2: Arthrobotrys dactyloides, mycelium with capture organs and assimilative hyphae marking a dead nematode stained with FDA and calcofluor white. 2a: observed with filter unit 13 (for FDA); 2b: after changing to filter unit A (for calcofluor white). Note the clearly visibly constricting rings before and after inflation. Bar represents 100 µm. Fig. 3: Individual hypha with branch double stained with FDA and calcofluor white and double exposed with Filter unit A (above) and 13 (below) like in fig 2. This staining allows even to study details inside the hyphae. Bar represents 20 µm.

Fig. 4: Section of a culture in soil on a microscopic slide of Arthrobotrys oligospora with hyphae, capture organs and dead nematodes (marked by the assimilative hyphae, stained with FDA, calcofluor white and rhodamin B. Note the good fluorescence of the assimilative hyphae. Filter unit A. Bar represents 100 Âµm.

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