EXCRETION OF GLYCOLATE BY THIOBACILLUS-NEAPOLITANUS GROWN IN CONTINUOUS CULTURE

Thiobacillus neapolitanus grown in minerals medium in a thiosulfate-limited chemostat excreted 15% of all the carbon dioxide fixed as 14C-organic compounds at a dilution rate (D) of 0.03 h-1. At D=0.36 h-1 this excretion was 8.5%. Up to a D of 0.2h-1 glycolate was the major excretion product. Glycolate excretion was maximal at a pO2 of 100% air saturation (a.s.) and not detectable at a pO2 of 5% (a.s.). Increasing the pCO2 of the gassing mixture to 5% (v/v), at a pO2 of 50% a.s. resulted in a lowering of the glycolate excretion from 3.5% of the total CO2 fixed to 1.8%. These results indicate that glycolate excretion in T. neapolitanus is due to oxygenase activity of D-ribulose-1,5-bisphosphate carboxylase. HPMS (2-pyridylhydroxymethanesulfonate), an inhibitor of glycolate metabolism, did not stimulate the glycolate production in T. neapolitanus. Glycolate excretion was not observed in thiosulfate-limited chemostat cultures of the obligately chemolithotrophic Thiomicrospira pelophila or in thiosulfate- or formate-grown cultures of the facultatively chemolithotrophic Thiobacillus A2. © 1979 Springer-Verlag.