Nutritional Requirements for Mycelial Growth of Milk-White Toothed Mushroom, Irpex lacteus (Agaricomycetes), in Submerged Culture.

Irpex lacteus, a medicinal fungus, is used in traditional Chinese medicine to treat chronic glomerulonephritis. In this work, a strain of I. lacteus was isolated from the fruiting body of a wild specimen and identified by ITS-5.8S ribosomal DNA sequencing analysis. Then the nutritional requirements and culture conditions for mycelial growth of I. lacteus in semisynthetic liquid media were investigated using the one-factor-at-a-time and orthogonal matrix methods. Optimum growth occurred at 30°C and 35°C. I. lacteus mycelia grew well at pH values between 3 and 9, suggesting that this strain is not sensitive to pH. The nutritional components, including 9 carbohydrates, 9 nitrogen compounds, 11 vitamins, and 10 mineral elements, were studied for their effects on mycelial growth in submerged cultures of I. lacteus. Among these variables, soluble starch, peptone, yeast extract, and calcium chloride were identified as required for optimum mycelial growth. The concentrations of each component were optimized using an orthogonal design, and the effects of medium composition on mycelial growth were found in the order soluble starch > yeast extract > peptone > calcium chloride. The optimal concentrations of these components for mycelial growth were determined to be 60 g/L soluble starch, 35 g/L peptone, 15 g/L yeast extract, and 0.6 g/L calcium chloride. Under the optimum medium and culture conditions, the maximum biomass reached 13.73 g/L after 3 days in submerged culture, a value over twice that reached using the basal medium. These results provide a basis for further physiological study and industrial fermentation of I. lacteus.