Effect of pH on Glycolate and Ammonia Excretion in L-MSO Treated Chlorella Cells

Abstract

Abstract The effect of pH changes on the excretion of ammonia and glycolate from algal cells into the medium was investigated in L-MSO (final concentration, 0.5 mм) -treated High-and Low CO2-cells of Chlorella vulgaris 211-11 h. The excretion was analyzed in the condition in which the cells were continuously gassed with air at 25 °C. At the values tested, generally more ammonia was excreted in L-MSO-treated Low CO2-cells than in L-MSO treated High CO2-cells. In both kinds of algal cells more ammonia was excreted at low pH-values and absolutely no ammonia was excreted at pH 8. In the dark, no or only slight ammonia excretion was observed in both L-MSO-treated High and Low CO2-cells. Under all these conditions no or only very low glycolate excretion was observed in both L-MSO treated High and Low CO2-cells. In High CO2-cells rates of photosynthesis were high at pH 6 and lower at higher pH values. On the other hand Low CO2-cells showed practically little dependence of photosynthetic rates on the pH. This result might indicate that the major part of the ammonia excretion observed, was not due to the inhibition of photosynthesis at acid pH values. It is known that ammonia excretion in L-MSO treated algal cells is due to the inhibition of the refixation of ammonia which originates from the glycine-serine aminotransferase reaction in the glycolate pathway. Our results demonstrate that glycolate production and glycolate metabolism are more intense at low pH values when compared to high pH values. This is valid for both High and Low CO2-cells. Low CO2-cells in Chlorella vulgaris 211-11 h exhibit a more active glycolate metabolism than High CO2-cells.