EFFECT OF HIGH NITRATE CONCENTRATIONS ON GROWTH AND NITRATE UPTAKE BY FREE-LIVING AND IMMOBILIZED CHLORELLA-VULGARIS CELLS

Growth and nitrate uptake were studied on free-living and immobilized Chlorella vulgaris cells cultivated in medium containing different nitrate concentrations. First, the effect of nitrate concentrations on growth indicated that cells can live in the presence of high concentrations as high as 97 mM. Although no lethal effect on cells was observed such concentration a slow down in growth and a decrease in biomass produced was observed. The rate of nitrate uptake increased with the nitrate concentration in the medium. The maximum uptake rate was reached in first days of culture in both free-living and immobilized cells. The rate dropped more rapidly for cells growing in 2 mM nitrate than for cells growing in higher nitrate concentration. The maximum rate was very much the same for free-living and immobilized and was within the order of 0.45 to 0.57 mug NO3 h-1 10(-6) cells. Immobilization modified the changes of nitrate uptake rate for concentration higher than 2 mM.