Improving the production of ectomycorrhizal fungus mycelium in a bioreactor by measuring the ergosterol content

The cultivation of some ectomycorrhizal fungi growing in bioreactors under submerged aerobic conditions was modified by regulating the cultivation parameters and determining the optimum duration of the process. For this goal, the active mycelium was determined by quantifying its ergosterol content. Lactarius deliciosus (strain LDF5) and Suillus mediterraneensis (strain 35 AM) were cultivated in a BRAUN Biostat(R)B bioreactor under the following fermentation conditions: 23 degreesC, pH 5.5, 60 % dissolved oxygen, 100 rpm stirring, and 1.2-2 L/min air flow. In addition, several cultivation conditions were assayed for L. deliciosus. During the fermentation cycle, samples were taken at different times. Ergosterol was extracted and quantified using high-performance liquid chromatography (HPLC). The quantity of ergosterol in L. deliciosus increased with the age of the culture up to 4.7 mug/mg (17-day-old culture). In the case of S. mediterraneensis, this quantity increased up to day 11 of the cultivation, and then it decreased. Three days after the addition of fresh medium, a maximum of 8.9 mug/mg was reached. On the other hand, the highest ergosterol content in L. deliciosus (6.3 mug/mg) was obtained using MMN medium with the addition of agar.