MOLD AND YEAST DIFFERENCES

The fungi comprise a large group of eukaryotic nonphotosynthetic organisms that include such diverse forms as slime molds, water molds, mushrooms, puffballs,bracket fungi, yeasts, and molds. Fungi belong to Kingdom Myceteae. The study of fungi is called mycology.
Myceteae consist of three divisions:Gymnomycota (slime molds), Mastigomycota (water molds and others), and Amastigomycota (yeasts,molds, bracket fungi, and others). It is the last division that we will study in this exercise.
Fungi may be saprophytic or parasitic and unicellular or filamentous. Some organisms, such as the slime molds,
are borderline between fungi and protozoa in that amoeboid characteristics are present and fungi like spores are produced.The distinguishing characteristics of the group as a whole are that they (1) are eukaryotic, (2) are non-
photosynthetic, (3) lack tissue differentiation,(4) have cell walls of chitin or other polysaccharides, and (5)propagate
by spores (sexual and/or asexual).
In this study we will examine prepared stained slides and slides made from living cultures of yeasts and molds.
Molds that are normally present in the air will be cultured and studied macroscopically and microscopically.In addition, an attempt will be made to identify the various types that are cultured.Before attempting to identify the
various molds, familiarize yourself with the basic differences between yeasts are essentially unicellular and molds are multicellular.

MOLD AND YEAST DIFFERENCES

Species within the Amastigomycota may have cottony (moldlike) appearance or moist (yeasty) characteristics that set them apart. As pronounced as these differences are, we do not classify the various fungi in this group on the basis of their being mold or yeast. The reason that this type of division doesn’t work is that some species exist as molds under certain conditions and as yeasts under other conditions. Such species are said to be dimorphic, or biphasic. The principal differences between molds and yeasts are as follows

Molds

Hyphae
Molds have microscopic filaments called hyphae (hypha, singular, if thefilament has crosswalls, it is referred to as having septatehyphae. If no crosswalls are present, the coenocyticfilament is said to be nonseptate, or
aseptate.
Actually,most of the fungi that are classified as being septate are incompletely septate since the septae have central openings that allow the streaming of cytoplasm from one compartment to the next. A mass of intermeshed hyphae, as seen macroscopically, is a mycelium.

Asexual Spores Two kinds of asexual spores are seen in molds: sporangiospores and conidia.

Sporangiospores are spores that form within a sac called a sporangium. The sporangia are attached to stalks
called sporangiophores,.

Conidia are asexual spores that form on specialized hyphae called conidiophores. If the conidia are small they are called microconidia; large multicellular conidia are known as macroconidia

•Phialospores: Conidia of this type are produced by vase-shaped cells called phialides. that Penicillium and Gliocadium produce this type.

• Blastoconidia: Conidia of this type are produced by budding from cells of preexisting conidia, as in Cladosporium, which typically has lemon-shaped spores.

•Arthrospores: This type of conidia forms by separation from preexisting hyphal cells. Example: Oospora

•Chlamydospores: These spores are large, thickwalled, round, or irregular structures formed within or on the ends of a hypha. Common to most fungi, they generally form on old cultures. Example: Candida albicans.

SexualSpores Three kinds of sexual spores are seen in molds: zygospores, ascospores, and basidiospores

Zygospores are formed by the union of nuclear material from the hyphae of two different strains.

Ascospores, on the other hand, are sexual spores produced in enclosures, which may be oval sacs or elongated tubes.

Basidiospores are sexually produced on club-shaped bodies called basidia.Abasidium is considered by some to be a modified type of ascus.

Yeasts

Hyphae
Unlike molds, yeasts do not have true hyphae. Instead they form multicellular structures called pseudohyphae.

AsexualSpores The only asexual spore produced by yeasts is called a blastospore, or bud.
These spores form as an outpouching of a cell by a budding process. It is easily differentiated from the parent cell by its small size. It may separate from the original cell or remain attached. If successive buds remain attached in the budding process, the result is the formation of a pseudohypha.