Excretion of Glycolic Acid by Chlorella during 



Photosynthesis* 



N. E. TOLBERT and L. P. ZILL, Biology Division, Oak Ridge National 



Laboratory, Oak Ridge, Tennessee 



Chlorella cells that had fixed NaHC^^Os for a few minutes were 

 found to excrete 3% to 10% of the fixed C^* as glycolate-C^* into the 

 aqueous nutrient medium. Glycolate was the only organic anion ex- 

 creted which could be detected and analyzed by paper and column 

 chromatography. Analysis of the soluble cellular constituents by 

 paper chromatography revealed the expected photosynthetic prod- 

 ucts inside the cell. During steady-state photosynthesis, 10 to 100 

 times as much glycolate was in the supernatant as inside the cells. 

 Normally, 3 to 8 mg. of glycolate per liter of cultures was obtained 

 from actively growing algae. Lewinf has recently found about twice 

 as much glycolate in the media from cultures of Chlamydomonas. 



The rapid excretion of glycolate by Chlorella is dependent on all 

 the factors influencing active bicarbonate fixation: (a) the presence 

 of bicarbonate, (b) aerobic conditions, and (c) light for active photo- 

 synthesis, since there must be a net bicarbonate uptake. In addition, 

 the younger cultures in the more active phases of growth and photo- 

 synthesis excrete a proportionately larger amount of glycolate. In 

 media above pH 5.5, the excretion is at a constant percentage rate of 

 the total fixed, whereas in more acid cultures the excretion of glyco- 

 late decreases until at pH 2.5 it becomes zero. 



Glycolate excretion and absorption may represent a glycolate- 

 bicarbonate anionic exchange across the Chlorella cell wall without 

 the necessity of a similar cationic shift. Since bicarbonate uptake 

 during photosynthesis and excretion during respiration represent a 

 major ionic movement, a balance of it with some other diffusible anion 

 would lessen an undesirable loss or absorption of cations. If a Donnan 



* Work performed under U.S. Atomic Energy Commission contract No. W- 

 7405-eng-26. A detailed report on the identification of glycolic acid and environ- 

 mental conditions affecting this excretion is being published elsewhere. 



t LeA\iu, R. A., personal communication. 



228 



