Filamentous fungal growth assay: correlation between [U-14C] glucose uptake and dry weight determinations

The filamentous fungus Trichophyton mentagrophytes was grown in [U-14C] glucose supplemented nutrient broth. Growth was monitored in 200 microliter microcultures and 5 ml macrocultures by measuring the incorporation of 14C into trichloroacetic acid-insoluble macromolecules and in macrocultures by dry weight determination. Adjustment of the specific activity of the [U-14C] glucose medium supplement from 1080 muCi/mmole to 108 muCi/mmole decreased the rate of isotope uptake and prolonged availability so that growth beyond 36 h could be monitored radiometrically. The dry mycelial weight of the fungus was directly proportional (r = 0.995) to the amount of isotope incorporated. Isotope uptake in microcultures and macrocultures was kinetically identical. These data clearly indicate that the uptake of 14C by T. mentagrophytes can be used to monitor fungal growth accurately in both macrocultures and microcultures.