Colorimetric assay for active biomass quantification of Fusarium fujikuroi

A colorimetric assay has been developed for quantitative analysis of active biomass of Fusarium fujikuroi, based on the reduction of the tetrazolium salt 2,3-Bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) when menadione was present as an electron coupling agent. The optimum assay-conditions were set as 200 μg/ml XTT, 5 μM menadione and one-hour reaction time. Under these settings, the produced formazan displayed a linear relationship with F. fujikuroi biomass. This method was subsequently applied to evaluate the cell growth behavior, which showed a positive correlation with the carbon source consumption and gibberellin biosynthesis under the industrial fermentation conditions. Our results showed that the XTT-menadione assay is a valuable tool in analyzing the industrial fermentation process of F. fujikuroi, especially when the medium contains insoluble and complex components. [Display omitted] •The selected assay conditions are 200 μg/ml XTT, 5 μM menadione and 1 h reaction time.•The produced formazan showed in a linear relationship with the fungal biomass.•The biomass behavior showed a positive correlation with the glucose level.•The cells secreted GA3 in the stationary phase, especially the late stationary phase.