IMPROVED pH CONTROL OF FUNGAL

SUMMARY A number of fungi grew well in the presence of relatively high concentrations (40 mM) of phosphate and MES [2-(N-morpholino) ethane sulfonic acid] buffers at either pH 5.5 or 7.0. In certain instances better growth and sporulation were observed than that found using more conventional growth media (malt, Czapek-Dox) that lack any marked buffering capacity. EMTA (3,6-endomethylene-1,2,3,6-tetrahydro-cisphthalic acid) could be used as a buffer for fungal culture media with certain species only. As good growth and no major change in chemical composition occurred, these buffers are recommended for use in high concentration to eliminate pH variation in comparative physiological studies. The pH of a culture medium strongly influences fungal growth, sporulation, and metabolite production. Conventional culture media (e.g., Czapek-Dox, malt, potato dextrose, Sabouraud agars) used for taxonomic and physiologic growth studies of fungi have relatively low buffering capacities. Similarly, most commercially available media lack a specific buffer, predicated on financial grounds, or rely upon a peptone component to stablize pH. Thus, fungi grown on them can produce large changes in pH which will vary according to the fungal strain, its growth rate, the substrate, and environmental conditions. In spite of this inadequacy, conventional media are used in laboratory batch cultures without further attempt at pH control. With defined media reliance is frequently placed upon the orthophosphate content of the medium which must serve as a nutrient source and as a buffer. Cochrane (1958, p. 301) has noted optimal concentra