Choice between autotrophy and heterotrophy in Pseudomonas oxalaticus. Utilization of oxalate by cells after adaptation from growth on formate to growth on oxalate

1. The labelling patterns of phosphoglycerate obtained from formate-grown or oxalate-grown Pseudomonas oxalaticus after exposure for 15sec. to ¹⁴C]formate or ¹⁴C]oxalate respectively were determined. 2. The phosphoglycerate obtained from the formate-grown cells contained 78% of the radioactivity in the carboxyl group. This is in accord with that predicted for operation of the ribulose diphosphate cycle of carbon dioxide fixation. 3. The labelling pattern of the phosphoglycerate obtained from the oxalate-grown cells approached uniformity, as predicted for the heterotrophic pathway of oxalate assimilation. The departure from complete uniformity may have been due to concurrent ¹⁴CO₂ fixation into C₄ dicarboxylic acids. 4. The labelling pattern of phosphoglycerate obtained from cells that had just started to grow on oxalate after adaptation from formate was determined after incubation of the cells for 15sec. with ¹⁴C]oxalate. This pattern approached uniformity. 5. The pathway of incorporation of ¹⁴CO₂ into cells that had just started to grow on oxalate after adaptation from formate, in the presence of either formate or oxalate as energy source, was studied by chromatographic and radio-autographic analysis. 6. It is concluded from the isotopic data that a mixed heterotrophic–autotrophic metabolism, with the former mode predominating, operates in the initial stages of growth on oxalate after adaptation from growth on formate.