Optimal conditions for accumulation of bioavailable iron in Saccharomyces cerevisiae cells.

Growth and proliferation of brewer's yeast Saccharomyces cerevisiae in the presence of different Fe2+ levels was studied with the aim of finding optimal conditions for a maximum accumulation of bioavailable iron bound to constituents of yeast cells. The results demonstrated that iron stimulates growth and proliferation only under conditions of intensive aeration. Iron accumulation and the effect of aeration were examined in the presence 3.6 microM - 7.2 mM Fe2+, while its content in the cells after 20 h cultivation was determined by atomic absorption spectrophotometry. Control cultures were grown in no iron added medium. Further experiments revealed that iron concentrations ranging from 3.6 microM to 3.6 mM were beneficial to growth and proliferation, while higher levels did not affect these processes. The above range of iron concentrations also led to a more extensive iron accumulation, while further increase expressed no effect. So, Fe2+ concentration of 3.6 mM, enabling its high accumulation within the cells, while not negatively affecting biomass yield was selected for further studies. Iron uptake led to the modifications in transport of several other elements (Ca2+, Zn2+, K+ and Na+) and thus to the change in ion composition of the cells in comparison with the corresponding control.

Superoxide dismutase biosynthesis by two thermophilic bacteria.

Some high-molecular weight antioxidant defense system components of two thermophilic bacteria isolated from spa waters of Serbia (Yugoslavia) and identified as Bacillus stearothermophilus and Thermothrix sp. were studied. In addition to superoxide dismutase (SOD; EC 1.15.1.1), qualitative analyses demonstrated the presence of catalase (EC 1.11.1.6), peroxidases and oxidases in both bacterial strains. Cell-free extracts were subjected to nondenaturing polyacrylamide gel electrophoresis (PAGE) and SOD activity in the eluates of the corresponding bands was examined in the presence of several specific inhibitors. A slight decrease of SOD activity observed in the presence of 0.3 M potassium cyanide and its complete insensitivity to hydrogen peroxide (5 mM) and sodium azide (20 mM) action suggest that the enzyme occurring in the two thermophiles represents Mn SOD. A high SOD activity recorded in cell-free extracts strongly recommends these two bacterial strains as potential producers of this important antioxidant defense system component at industrial scale.