NITRATE REMOVAL BY ANTARCTIC PSYCHROPHILIC YEAST CELLS UNDER HIGH SALT CONDITIONS

We researched nitrate removal in water with high salt concentrations at low temperature using Candida sp. which was isolated from the upper layer of Lake Vanda in the McMurdo Dry Valleys, Antarctica. The strain was cultured in a synthetic medium that contained nitrate as the sole nitrogen source. The time course for the growth, and the nitrate and the total organic carbon (TOC) removals were examined aerobically in the presence of 0-20% NaCI at 5OC. The effects of pH and the C/N ratio on the removal of nitrate were studied. Candida sp. can remove more than 90% of nitrate up to an NaCI concentration of 10% in the medium. As compared with 0% NaCI, 4% NaCI in the medium did not influence the growth rate and the removal of nitrate and TOC, but, at NaCI of 8 and lo%, the growth and removal of nitrate and TOC were decreased slightly. The yeast did not grow in the medium that contained NaCI of 15 and 20%. At pH of 3 to 7, yeast cells exhibited a similar removal nitrate level but it decreased at pH 1 and 2. The removal of nitrate increased with an increase in the C/N ratio and the nitrate in the medium was completely removed at a C/N ratio of 40. Nitrite was not observed in the cultured broth throughout the experiments. The amino acid composition of the yeast cells did not change with nitrogen sources.