Relationship between fluorescein diacetate-stained hyphae and oxygen utilization, glucose utilization, and biomass of submerged fungal batch cultures.

The relationship between fungal activity and staining with fluorescein diacetate (FDA) was investigated by growing Penicillium citrinum and Rhizoctonia solani in submerged batch cultures at different initial glucose concentrations and aeration rates. A modified FDA staining method, similar to the Jones and Mollison technique (P. Jones and J. Mollison, J. Gen. Microbiol. 2:54-69, 1948), was developed to assess both total and FDA-stained hyphae. In previous studies, soil hyphae stained with FDA were considered viable. However, determination of a quantitative relationship between FDA staining and fungal activity is necessary before such an assumption can be made. Growth rates and the rate of change in the percentage of FDA-stained hyphae were significantly correlated. The regression equation calculated for the relationship was: growth rate (mg . ml-1 . h-1) = 0.34 + 1.1 (rate of change in the percentage of FDA-stained hyphae [. ml-1 . h-1]). Changes in activity as measured by O2 utilization, glucose utilization, and biomass correlated significantly with changes in the percentage of FDA-stained hyphae, although the relationships among these parameters were different for each fungal species. Fungal growth stage was also correlated with the percentage of FDA-stained hyphae. Staining was 10% or greater during fungal growth and less than 10% during the late growth, stationary, and death phases. Thus, the rate of change in the percentage of FDA-stained hyphae can be used to predict fungal activity rate changes for single fungal cultures and growth rates for mixed fungal cultures, and the growth stage can be assessed by the percentage of FDA-stained hyphae.