Glycolate biosynthesis by Scenedesmus and Chlorella in the presence or absence of NaHCO3

Abstract

Both Scenedesmus and Chlorella excreted comparable quantities of glycolate. Glycolate formation was dependent upon light and oxygen, but occured in the absence of added CO₂ or NaHCO₃ for net photosynthesis. In an environment of 3000 ft. c. light and an atmosphere of oxygen, about 35 μg glycolate were excreted per hour per milliliter 1% (v/v) algae without NaHCO₃ or CO₂. Upon addition of NaHCO₃ the rate increased to about 55 μg. Glycolate formation in the light in the absence of CO₂ may result from photometabolism of algal polysaccharides. Glycolate excretion by Scenedesmus occurred at all pH values between 6.5 and 9.5 and was not related to utilization of bicarbonate. Scenedesmus obliquus excreted glycolate when existing in plates of four or eight cells, but not when present as small individual cells. At pH 9 ¹⁴C fixation by Scenedesmus was faster than fixation by Chlorella. There was no significant difference in products of ¹⁴C fixation formed by Scenedesmus at pH values between 6.5 and 9.5. For unknown reasons α-hydroxy-2-pyridinemethanesulfonate stimulated CO₂ fixation by Scenedesmus by at least 100%. This sulfonate had no effect on glycolate excretion nor upon the distribution of ¹⁴C among the products of ¹⁴CO₂ fixation by Scenedesmus.