Effects of Varying Nutritional and Cultural Conditions on Growth of the Ectomycorrhizal Fungus Pisolithus tinctorius SMF

The culture conditions and nutritional requirements for enhanced mycelial growth of the ectomycorrhizal fungus P. tinctorius SMF were determined in flask scale experiments. Optimum culture conditions for growth of P. tinctorius SMF in a further modified Melin-Norkrans broth were as follows; temperature 25~$27^{\circ}C$, agitation 120 rpm, and pH 4.0. P. tinctorius SMF utilized various carbon sources including monosaccharides, disaccharides, and polysaccharides. D-Glucose and mannitol were respectively the first and second most suitable carbon sources for mycelial growth. With D-Glucose as the principal carbon source, supplementation of modified Melin-Norkrans (MMN) broth with Lysine (800 mg/l), Glutamic Acid (500 mg/l), or Proline (50 mg/l) enhanced mycelial yields 63%, 34%, and 22% respectively as compared to growth in medium lacking amino acids. ThiaminㆍHCl＋biotin＋pyridoxine supplementation also enhanced growth. As compared to mycelial growth in the MMN medium, growth of P. tinctorius SMF was enhanced 120% in MMN broth when the carbon/nitrogen ratio was 25/1 in citrate buffer at pH 4.5, and growth was 50% greater in MMN broth of carbon/nitrogen ratio with a 10/1~20/1 without using the buffer. Standard conditions established for growth of P. tinctorius SMF in MMN broth were 25~$27^{\circ}C$, agitation 120 rpm, buffered to pH 4.0 with citrate, in MMN medium containing 10 g/l D-glucose supplemented with 800 mg/l lysine. In this medium the carbon/nitrogen ratio was 20/1~25/1, and the maximal mycelial yield ($Y_{x/s}$ ) was 0.472 (4.72 mg/ml) after 7 days of incubation, as compared to 0.214 (2.14 mg/ml), when the fungus was grown in standard MMN broth.