Carbon/nitrogen relationships of fungus culture media

Summary and Conclusions Four basic nutrient types are described and discussed in special reference to the ratios between carbon source materials and nitrogen source materials. These include habitat, natural nutrients, semisynthetic nutrients and synthetic nutrients. Special emphasis is placed on the use of such nutrients in agar media for the primary isolation of fungi from various types of habitat materials such as soils and sewage.It is suggested that a basic C:N ratio for such nutrient agars lies at about 9 or 12 to 1, that increasing this ratio tends to overenrich the culture thus encouraging the formation of intracellular or extracellular carbon-carrying compounds, and that decreasing the ratio tends to encourage the formation of nitrogen-carrying storage products. Both conditions tend to produce staling substances more rapidly, tend to decrease discreteness of colonies, tend to produce more diffuse, less easily counted growth, and tend to develop less readily identifiable colonies.It is implied that if a C:N ratio more or less approximating that found in an agar containing plant parts, or limited nutrients plus plant parts, were used in a medium designed for primary isolation of fungi from natural materials, such a medium would have many advantages over currently popular media used for this purpose.