Introduction to Lab 4: Ex. Fungi - Molds

The purpose of this exercise is to study some representative genera of molds.

This exercise will be entirely covered with the use of demos. The reason for this being: molds can be hazardous organisms to

study in the lab.

Molds are identified based on physical structures that they produce when grown on the surface of artificial culture media.

Structure: Molds are filamentous structures (hyphae) that intertwine to form a mass called the mycelium.

The hyphae that are responsible for the absorption of nutrients from the environment are called the vegetative hyphae and are found close to or embedded in the culture medium.

When the mold starts producing spores for reproduction (especially asexual) these spores are borne above the surface to facilitate their dispersal into the environment. The hyphae that produce the asexual spore structures are hence called aerial hyphae.

Since the spore structure is ideally suited for its purpose of easy dispersal, they are very light and can be dislodged very easily from the aerial hyphae.

Hence extra precautions have to be used when handling mold cultures. They can be opened only under a containment hood with appropriate personal protection to avoid exposure to these spores.

Hyphae may be coenocytic or septate. When present septa may be of one of three kinds.

Asexual structures are the spores found within a sac or without a sac but associated with other structures.

Sexual spores are the features used in classification of Fungi. They may be of different kinds.

Specimens on demo: these include stained slides and cultures of mold growth for observation.

Mold slides are prepared by tease mount or slide culture preparations.Appropriate stains are used to color the filaments and other structures. Cultures of molds are grown using culture media that are suited for their growth, i.e., acidic pH media.

Genera: Zygomycotina – Rhizopus sp., Phycomyces sp.

Ascomycotina – Aspergillus sp., Penicillium sp.

Rhizopus - coenocytic hypha, (specific characteristic – rhizoids and columella in sporangia) asexual structures -sporangia and spores, sexual spore –zygospore.

Phycomyces – slide showing zygospore formation; culture plate with the two opposing strains and zygospores formed at the meeting of the hyphae of opposing strains.

Ascomycotina -Aspergillus niger, A. ochraceus – septate hypha, conidia with vesicle

and sterigmataspecific – afro head appearance to conidial head.Plate – black pigmented, powdery growth

Penicillium – septate hypha, conidia with sterigmata specific – branched conidiophores; paint brush-like appearance to the conidial structures.Plate – greenish and white growth, powdery appearance