Observations on the Fine Structure of Saccharomyces cerevisiae as Affected by Biotin Deficiency

Abstract

SUMMARY: Growth of a biotin-requiring strain of Saccharomyces cerevisiae in a medium containing a suboptimal concentration of biotin caused changes in the fine structure of the yeast as revealed by electron microscopy. The cytoplasmic and vacuolar membranes in yeast grown in unsupplemented biotin-deficient medium were particularly susceptible to polymerization damage and appeared to split along the lipid layer. Similar changes in the appearance of the cytoplasmic membrane were observed in biotin-optimal yeast after treatment with aqueous butanol. Yeast grown in unsupplemented biotin-deficient medium also contained a slightly greater number of large storage granules as compared with exponential phase biotinoptimal yeast. When grown in aspartate-supplemented biotin-deficient medium, the yeast had much thicker cell walls than when grown in unsupplemented biotin-deficient medium. In yeast grown in oleate-supplemented biotin-deficient medium, the cytoplasmic membrane split less extensively along the lipid layer as compared with yeast grown in unsupplemented biotin-deficient medium. Organisms grown in biotin-deficient medium supplemented with aspartate + oleate resembled those grown in biotin-deficient medium supplemented with only aspartate in possessing thick cell walls, but otherwise were similar in fine structure to yeast grown in oleate-supplemented biotin-deficient medium. The storage granules in yeast grown in biotin-optimal medium and in unsupplemented biotin-deficient medium stained strongly with Sudan Black B, a lipophilic stain, and their appearance in increased numbers in yeast grown in unsupplemented biotin-deficient medium was accompanied by an increase in the lipid content of the yeast as compared with biotin-optimal yeast. The significance of these changes in fine structure is discussed in relation to changes in chemical composition previously reported to result from an imposition of biotin deficiency in the yeast.