paper 9

Media and incubation effects on morphological characteristics of Penicillium and Aspergillus

Toru Okuda, Maren A. Klich*, Keith A .Seifert**, and Katsuhiko Ando*** *USDA Southern Regional Research Center, New Orleans, USA; **Cereal and Oilseed Research Centre, Agriculture and Agri-food Canada, Research Branch, Ottawa, Canada; ***Kyowa Hakko Kogyo Co., Tokyo, Japan

In: Integration of Modern Taxonomic Methods for Penicillium and Aspergillus Classification. Ed. by Rob A. Samson and John I. Pitt. Harwood Academic Publishers, Australia, 2000. pp83-99.

Every scientist involved in Penicillium/Aspergillus identification is aware that a variety of known and unknown factors affect colony and microscopic characteristics. Since Thom and Raper, reproducibility in taxonomic work has been sought by standardizing cultivation parameters. Introduction of new methods has resulted in a diversity of protocols employed in different laboratories. Few intensive studies on these factors or variables have been carried out. To summarize the variability in routine methods for Penicillium/Aspergillus taxonomy, we distributed a questionnaire to the members of the International Commission on Penicillium & Aspergillus. In this study we considered the following variables: medium ingredients, types of Petri dishes, volume of media, method of inoculation, and incubation conditions including temperature, air exchange, duration, and sporadic exposure to light. In our pilot studies, the most important factors strikingly affecting colony appearance and growth were volume of media and air exchange. Inoculum size and occasional light influenced the colonies to a lesser extent. Differences in water or brands of yeast extract or agar did not greatly affect cultural characteristics.

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