Zinc is one of trace elements of fundamental importance to human health. Inadequate intake of this metal can effect any of over 200 enzymes. The structural function of zinc is its role in the structure of proteins and membranes. Zinc finger proteins have been found to regulate gene expression by acting as transcription factors. Zinc also plays a role in cell signaling, has been found to influence nerve impulse transmission and hormone release. Adequate zinc intake is essential in maintaining the integrity of the immune system. HIV infected individuals are particularly susceptible to zinc deficiency.

Many species of mushrooms have been found to be highly potent immune system enhancers. Lentinus edodes is one of medicinal mushrooms from which extracted highly purified polysaccharide fraction (lentinan) is an approved drug, used in cancer treatment as well as in AIDS research. Hot water and alcohol extracts from L. edodes mushroom mycelium and culture media (LEM, LAP) demonstrate strong immunostymulating and antioxidant activity. The chemical composition of cultivated in submerged culture mycelial biomass, which can be used to obtain pharmacologically active extracts, depends on the nutritional conditions. The present study involves the optimization of medium constituents for both - L. edodes mycelium growth and high zinc content in mycelial biomass, possibly in form of a highly bioavailable organic compounds. High zinc content in mycelial biomass possibly would enhance immunostymulating and antioxidant activity of mushroom extracts.

The effect of Zn(II) on the mycelial growth and chemical composition of Lentinus edodes submerged cultured mycelial biomass was investigated in shake flask culture. Culture media were enriched in zinc by addition of ZnSO₄ in concentration range from 0 to 90 ppm, added to the medium before inoculation. The Zn(II) content in cultivated mycelial biomass was determined by use of the atomic absorption spectrometry (AAS) on GBC Avanta Ultra Z spectrometer. Zinc concentration expressed in mg% of mycelial dry mass rose from 90 mg%, estimated for mycelium cultivated in not enriched in Zn (II) medium, to 400 mg% for mycelium cultured in medium supplemented in 30 ppm of zinc. The higher than 30 ppm concentration of Zn(II) in medium affects lower zinc content in mycelial dry mass. Zinc concentration in medium strongly affects on the mycelial growth. Productivity of the mycelium rose proportionally to the increasing concentration of Zn(II) in medium. The highest mycelial growth was recorded for media enriched in Zn(II) in concentration of 30 ppm. Higher than 30 ppm concentration of Zn (II) in medium acts depressive on the mycelial growth. Optimal pH of medium for zinc accumulation was estimated by cultivation of Lentinus edodes mycelia in media of pH ranging from 3.5 to 7, enriched in 30 ppm of zinc(II). The optimal pH of medium for zinc accumulation was 7. Proportionally to the increasing concentration of zinc(II) in medium rose the percentage of this metal adsorbed on the cell surface, easy to remove by washing of the mycelium with the 0.05 molar EDTA solution. The value of the adsorbed on the cell surface zinc percentage changed in range from 30% to 70% for concentrations of Zn(II) in medium rising from 0 to 90 ppm.

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1. SUBMERGED CULTIVATION OF STREPTOMYCES TSUKUBAENSIS IN MEDIA COMPOSED OF WASTE PRODUCTS OF FOOD INDUSTRY.