The methodology used here is based on the reaction catalysed by hydrogenases of the functional hyphae. They will cleave the yellow tetrazolium salt MTT ([3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide) to its purple derivative MTT-formazan, which can be dissolved in isopropanol and quantified by spectrophotometry.