Biomass production of the mycorrhizal fungus Suillus grevillei: effect of pH and ammonium.

The ability of the ectomycorrhizal fungus Suillus grevillei (Klotzsch) Singer to grow in agitated submerged culture was investigated by employing the Marx-Melin-Norkrans (MMN) medium. The operating conditions suitable for improving the biomass production were determined. Batch experimental tests were carried out in either shake flasks or a stirred tank reactor. The results showed that at least two factors strongly affected the fungal growth, namely the pH and the ammonia-nitrogen concentration in the medium. By controlling the acidity in the pH range 4-5 with a Na-citrate buffer solution and introducing the ammonia-nitrogen in a step-feed way (without exceeding a concentration of approximately 0.07 kg N/m3), the exponential growth phase continued for longer than that of the control culture (no stationary phase seemed to be reached after 17 days) and an approximately 2-fold increase of the biomass/substrate growth yield was obtained compared with the control culture.