S U M M A R YThe wall of basidiomycetous and related yeasts showed a lamellar structure in sections of both budding cells and hyphae fixed with potassium permanganate. The yeasts also had a typical way of bud formation and septation. These features differ from those recorded for ascomycetous yeasts. In the hyphae of some species septa1 pores were observed which were either dolipores or simple pores.

Abstract. Cells of 3 yeast species capable of assimilating methanol have been examined by electron microscopy. When grown on methanol as the sole source of carbon and energy they contained many microbodies. Cells grown on glucose or ethanol either did not contain such bodies at all, or only to a limited extent.Key words: Yeasts --Methanol --Microbodies.Since the recent discovery of a number of yeasts which can utilize methanol as the sole source of carbon and energy, much progress has been made with respect to the enzymology of methanol metabolism in these organisms. It has been shown that the dissimilation of methanol is mediated by a methanol oxidase, catalase, and NAD dependent formaldehyde--and formate dehydrogenases (Fujii and Tonomura, 1972). The same authors (1973) obtained indications that the ribulose phosphate pathway of formaldehyde fixation is involved in the assimilation of methanol in yeasts. However, as yet, nothing is known about the localization of the assimilatory and dissimilatory enzyme systems involved in methanol metabolism in the yeast cell. Recent work in our laboratories has revealed a special intracellular organization of a number of yeasts during growth on methanol. This communication describes observations made on the ultrastructure of these C1 utilizers. Microorganisms and Cultivation. Strains of Hansenula polymorpha de Morals et Maia, CBS 4732, Pichia pinus (Holst)Phaff, CBS 5098 and Candida boidinii Ramirez, CBS 2429 were grown in a mineral medium supplemented with vitamins and either methanol, ethanol or glucose (0.3 ~ w/v) as the sole source of carbon and energy (van Dijken and Harder, 1974). H. polymorpha was grown in batch and in chemostat cultures, whereas the other two species were batch-cultivated. Subcellular fractions were prepared via protoplast formation with snail gut enzyme (Helicase) followed by mechanical breakage in a Potter Elvehjem homogenizer and differential centrifugation. Electron Microscopy. For the preparation of specimens for sectioning, the yeast cells were harvested and washed with water. Two methods of fixation were employed: (1) with 1.5 ~ KMnO4 for 20 rain at room temperature, and (2) with 3 ~ glutaraldehyde in 0.1 M cacodylate buffer, pH 7.2 for 3 h at 0 ~ C, followed by washing in the same buffer and postfixation with 1 ~ OsO4 in cacodylate buffer for 16 h at 4 ~ C. During dehydration in an ethanol series, the cells were poststained with a saturated solution of uranyl acetate in 100~ ethanol. They were embedded in Epon 812, and part of the sections were stained with lead citrate. Freeze-etch replicas were made in a Balzer's unit as described by Moor (1964).

A new yeast species, Trichosporon adeninovorans, was isolated from soil by the enrichment culture method. Apart from adenine, the strain utilized uric acid, guanine, xanthine, hypoxanthine, 6,8-dihydroxypurine, putrescine, propylamine, butylamine, pentylamine, hexylamine and octylamine as sole source of carbon, nitrogen and energy. The structure of the cell wall of Tr. adeninovorans was ascomycetous. On the subcellular level growth on adenine or uric acid was accompanied with the development of microbodies in the cell. These cell organelles probably were the site of urate oxidase, an enzyme that, after growth on purine substrates, together with allantoinase was present at high activities. Low activities of adenine amidohydrolase and xanthine dehydrogenase were also demonstrated.

The wall of mature ascospores of Saccharomyces cerevisiae showed in sections under the electron microscope a dark outer layer and a lighter inner layer. The latter was composed of a greyish inner part and a light outer part. During germination, the spore grew out at one side and the dark outer layer was broken. Of the light inner layer, the inner greyish part became the wall of the vegetative cell, but the extended part of the cell had a new wall.

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