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 mu g/ml XTT, 5 mu M 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.