Biol/CSES 4684

PENICILLIUM

SOIL MICROBIOLOGY

This webpage was created by Lauren Barlow

1. IDENTIFYING CHARACTERISTICS:

Eukaryote.
Aerobic, saprophytic fungus.
Cells typically 0.75-5 x 2-6 microns.
Form a layer of conidophores and conidia on surface of colonies.
Condiogenous cells are flask shaped.
Conidia are small aseptate and shapes range from globose to cylindrical.
Conidia walls range from smooth to strongly roughened surfaces.
Some produce a telemorph with nonstiolate ascomatas.
Hyphae can be either aerial or submerged.
Colonies are gray-green to blue-green in color and have large numbers of dry conidiospores.
Spores are nearly always green.

The picture to the left shows a Penicillium conidiospore arrangement that is referred to as triverticillate.

2. TAXONOMIC DESCRIPTION:
Penicillium has vegetative mycelium that consist of hyphae that are either pale or brightly colored. The conidiophores grow perpendicular to the hyphae and at the apex the basal portion is relatively narrow. At the ends of these conidiophores are clusters of flask-shaped philiades. Here a branched fruiting structure is formed and consists of condiogenous cells. The cell wall consists of four layers in which the outermost layer is released when the spore swells and the other three innermost layers form the germ tube walls.

Penicillium is the largest group of fungi in soils and is very difficult to categorize. It can , however, be divided into groups depending on the branching structures of its spore-bearing conidiophores. Some species have no branching of conidiophores and are called monoverticillate and those that do have clusters of branches are called biverticillate. The third category is the triverticillate, which have a second order of branches and clusters of phialides.

Many species have a mycelium that is submerged within the first couple of millimeters on an agar surface. This allows the fungus to penetrate into the nutrient-rich substrate and obtain the necessary energy and nutrients. Conidiophores form directly from this submerged hyphae or coremia, which in turn promotes spore dispersal. Pencillium will grow larger, more complex conidial heads when grown from a substrate culture medium and form smaller, less complex heads when originating from the aerial hyphae. Certain isolates of Penicillium form roughenings on the walls of the conidiophores and others will have smooth walls depending on the surrounding environment. The fungus also produces secondary metabolites which can be toxic to fungal predators such as insects and vertebrates.

The picture above shows Penicillium in late growth phase.

3. ISOLATION AND ECOLOGY:
Penicillium can readily be isolated on Czapek's agar and malt-extract agar with Czapek's salts. Isolation media are best incubated for seven days in the dark at 25^o Celsius. Pencillium can grow in the temperature range of 22^o to 27^o Celsius and, in certain bacteriology labs, the cultures are grown at 37^o Celsius because this temperature correlates to the human body temperature and it is an optimum temperature to determine species differentiation. Penicillium grows optimally at neutral to slightly acidic pH. In order to have rapid and uniform fungal growth, yeast extract is usually added to media because this provides a source of trace minerals and organic nitrogen that is needed by Penicilllium. The Penicillium cultures will usually grow conidiophores; and conidia the same color as the agar on which it is grown. Cultures also form deposits of yellow, orange and red colored granules on aerial hyphal structures.

Penicillium is commonly found in temperate soils and can survive and even grow in low water activity environments. It also frequently inhabits soils that contain a high amount of organic matter, especially in forest soils that have abundant amounts of leaf litter on the surface.

Penicillium has many uses in the manufacturing industry and is commonly employed in such processes as the production of fermented foods, as a flavoring agent; and is most well known for producing the antibiotic, penicillin. Penicillin is produced in liquid culture by Penicillium chrysogenum, and the antibiotic is used primarily against Gram positive bacteria. Today, most penicillin is manufactured by synthetic processes.

Penicillium is a very common mold that is found in most households and is known to reqularly infect such foods as citrus, other fruits, and cheeses. Food contamination by Penicillium can be a serious problem to those who suffer from allergic reactions to the fungus.

The picture above is a Penicillium culture showing hyphal growth and spore capsules.

4. ADDITIONAL SOURCES OF INFORMATION
Perbedy, John F. (ed.) 1987. Penicillium and Acremonium. Plenum Press, New York.

Pitt, John I. 1979. The genus Penicillium and Its Telemorphic States, Eupenicillium and Talaromyces. Academic Press, New York.

Ramirez, Carlos. 1982. Manual and Atlas of the Penicillia. Elsevior Biomedical Press, New York.

Samson, Roberto A., and John I. Pitt, (eds.) 1987. Advances in Penicillium and Aspergillus Systematics. Plenum Press, New York.

5. LINKS TO OTHER SITES ABOUT PENICILLIUM
Penicillium Research at the University of Toronto

Penicillium website at the University of Minnesota