Examination of Mygologigal Specimens in the Scanning Electron Microscope

690

Transactions British Mycological Society

The work being done on the mycoflora of this area is supported by the Council for Scientific and Industrial Research, Pretoria, and by the Department of Agricultural Technical Services of the R. S. Africa. The author wishes to express his gratitude to Dr J. A. von Arx, Centraalbureau voor Schimmelcultures, Baarn, Netherlands, for his valuable suggestions and for reading the manuscript and preparing the Latin diagnosis. REFERENCES

GERDEMANN,J. W. (1953). An undescribed fungus causing a root rot of red clover and other Leguminosae. Mycologia 45, 548-554. McVEY, D. V. & GERDEMANN, J. W. (1960). The morphology of Leptodiscus terrestris and the function of setae in spore dispersal. Mycologia 52, 193-:200. M. C. PAPENDORF,

Department of Botany, The University, Potchefstroom, South Africa

EXPLANATION OF PLATE

26

Leptodiscus africanus Fig. I. Conidium, x 3600. Fig. 2. Hyphae with sessile conidia, x 1600. Fig. 3. Conidiophores and conidia, x 700. Fig. 4. Conidiophores and conidia, x 1700. Fig. 5. Culture on potato-carrot agar showing conidia, aggregation of conidia and part of a fructification on extreme left, x 350.

EXAMINATION OF MYCOLOGICAL SPECIMENS IN THE SCANNING ELECTRON MICROSCOPE

The technique of scanning electron microscopy allows solid specimens to be examined directly. There appears to be no previous published record of fungal structures having been examined in this manner. Before the introduction of the scanning microscope the only available method for examining the ultra-structure of the surface features of intact microbial specimens involved the preparation of carbon replicas which could then be examined in the transmission electron microscope. Alternatively the cell contents could be removed from the material, e.g. hyphae, spores and the wall preparation then shadowed with metals such as nickel/palladium or gold/palladium before examining in the transmission electron microscope. The present note reports the results of the examination of the surface features of the conidia of Acremoniella sp. IMI I II824) in the Stereoscan M.K. II electron microscope (Cambridge Instrument Co., Ltd.). The fungus was isolated from kaolin pellets, containing vanillic acid, during their incubation on the surface of soil (Jones & Farmer, 1967). This organism was examined at the Commonwealth Mycological Institute, Kew, and did not match any culture of the same genus maintained there (personal communication, Dr Onions). Preparations of aerial hyphae stained with lactophenol-cotton blue (PI. 27, fig. 3) and examined in the light microscope revealed one-celled conidia enveloped with what appeared to be a net-like veil. For examination in the scanning electron microscope the aerial hyphae, including the Trans. Br. mycol. Soc. 50 (4), Printedin Great Britain

Trans. Br. mycol. Soc.

Vol. 50.

Plate 26

(Facing jJ. 690)

Trans. Br. mycol. Soc.

Vol. 50,

Plate 27

I 4

2

____ 5

3

6

(Facing p. 691)

Notes and Brief Articles

691

conidia, were scraped from an agar slope and mounted on a dural specimen holder on a thin layer of nitro-cellulose, allowed to dry and coated with 500 A of evaporated gold/palladium. Evaporation of the metal was carried out from all directions to avoid shadowing effects. The surface features of the net-like veil could now be clearly seen (PI. 27, figs. I, 2). Ultra-thin sections of the conidia examined in the transmission electron microscope (A.E.!., E.M. 6 model) confirmed the presence of this secondary membrane. In addition, mycelial strands of a sterile fungus isolated from pellets similar to those referred to above were examined in a similar manner. On examination in the scanning microscope a verrucose appearance to the hyphal surface was observed (PI. 27, fig. 5). Ultra-thin sections of isolated walls of this material examined in a transmission electron micrscope confirmed the presence of wart-like protrusions on the wall surface (PI. 27, fig. 6). This verrucose appearance was not observed in young material (PI. 27, fig. 4). Research into the mode of attack of microbial lytic enzymes on fungal cell walls and the chemical analysis of these walls is being carried out in the Macaulay Institute (Jones & Webley, 1967). The above observations on hitherto undescribed fungal species may well prove of value in this connexion since attempts are being made to relate the chemical components of fungal walls to the ultra-structure observed. I am indebted to Miss Celia E. Moss, Electron Probe Department, Cambridge Instrument Company Ltd., for examining the specimens in their Scanning Electron Microscope and for taking the photographs PI. 27, figs. I, 2, 4 and 5. I also wish to express my thanks to Dr D. M. Webley for valuable discussion during these investigations. REFERENCES

D. & WEBLEY, D. M. (1967). Lysis of the cell walls of yeast (Saccharomyces cerevisiae) by soil fungi. Trans. Br. mycol. Soc. 50, 149-154. JONES, D. & FARMER, V. C. (1967). The ecology and physiology of soil fungi involved in the degradation of lignin and related aromatic compounds. ]. Soil. Sci. 18, 74-84. JONES,

D. JONES,

Department oj Microbiology, Macaulay Institute Jor Soil Research, Aberdeen

EXPLANATION OF PLATE

27

Figs. 1-3. Hyphae and one-celled conidia (arrowed) of Acremoniella sp. Figs. I, 2. Stereoscan photomicrographs ( x 2300) Fig. 3. Stained preparation (lactophenol-cotton blue) examined in light microscope (x 1100). Figs. 4-6. Hyphae of sterile fungus. Figs. 4, 5. Stereoscan photomicrographs (x 11300). Fig. 6. Ultra-thin section (stained uranyl acetate) of hyphal tip of smilar material shown in fig. 5 (x 23000). Note smooth surface of young hyphae in fig. 4, and warty surface (arrowed) of old hyphae in figs. 5 and 6.

(Accepted Jor publication 14 December 1966)

Trans. Br. mycol. Soc. 50 (4), Printed in Great Britain