Physiology of Candida utilis yeast in zinc-limited chemostat culture

Abstract

Candida utilis NRRL Y-900 was grown in aerobic continuous culture in a minimal salts medium with sucrose (1% w/v) as the carbon source. Increasing the concentration of zinc in the medium from 2.3 μM to about 30 μM results in an increase in the apparent critical dilution rate from 0.3 to 0.47 h−1, and in the maximum biomass productivity from 1.5 g dry weight per litre per hour (at D = 0.33 h−1) to 2.56 g per litre per hour (at D = 0.45 h−1). The maximum steady-state level of cell-associated zinc (at D = 0.4 h−1) is 4 nmol Zn2+/mg dry weight, during carbon-limited growth, and about 9 nmol Zn2+/mg dry weight when FeCl3 is omitted from the medium. At input zinc concentrations <20 μM, the cellular zinc concentration decreases linearly in proportion to the input zinc concentration and at <4.5 μM Zn2+ the culture becomes zinc-limited. Zinc-limitation results in a decrease in the growth yield Ysucrose from 0.54 to 0.38 g cells/g sucrose consumed, and Y0 from 22 to 13 g cells/g-atom O2, suggesting an altered efficiency of energy metabolism. The composition of the culture biomass with respect to protein and RNA content is not affected by zinc limitation.