ABSTRACT
Yeasts represent a growth form, of which about 1500 species (representing only 1% of all yeasts) have been described. Most yeasts reproduce asexually by budding, but a few do so by binary fission (Figure 9.1). Although yeasts are predominantly unicellular, some species with yeast forms may become multicellular through the formation of a string of connected budding cells known as pseudohyphae or true hyphae as seen in most molds (Figure 9.2). Yeasts typically measure 3-4 μm in diameter, but their sizes can vary enormously depending
on species, with some yeasts measuring over 40 μm. The morphological characteristics of yeast cell, ascospore, and colony are often used in combination with the physiological characteristics (e.g., the ability to ferment sugars for the production of ethanol) to identify yeast species.
