Efficiency of CO2 fixation in a glycollate oxidoreductase mutant of Alcaligenes eutrophus which exports fixed carbon as glycollate

Mutant strains of the facultative autotrophic bacterium Alcaligenes eutrophus blocked in glycollate utilization were isolated and characterized. One of the strains, AE161, which lacked glycollate oxidoreductase activity, excreted up to 1.2µmol glycollate/mg cell protein per hour during autotrophic growth. This mutant strain was used to study the efficiency of CO₂ fixation in terms of how much of the fixed carbon was excreted as glycollate under different conditions. Glycollate excretion was not detected during heterotrophic growth. Only 1% of the total CO₂ fixed was excreted as glycollate in an atmosphere of 4% CO₂ plus 20% O₂. The rate of glycollate excretion showed a large increase and CO₂ fixation decreased as the CO₂ concentration was lowered. Almost half (40–50%) of the total CO₂ fixed was excreted as glycollate in an atmosphere of 0.07% CO₂ plus 20% O₂.