Carbon assimilation by Pseudomonas oxalaticus (OX 1). 1. Formate and carbon dioxide utilization during growth on formate

Abstract

The incorporation of carbon from either[C14] formate or [C14] bicarbonate by cultures of Pseudomonas oxalaticus (OX 1) grown on formate has been studied. Isotope appeared in both the aqueous ethanol-soluble and protein fractions of the cells during 5 min. incubation periods. The distribution of radioactivity within the non-volatile constituents of these fractions, after incubation for from 12 sec. to 5 min., has been analysed by chromatography and radioautography. Over 80% of the radioactivity incorporated at the earliest time (12 sec.) into the ethanol-soluble fractions was present in phosphorylated compounds, and 5% in malate, with either [C14] formate or [C14] bicarbonate. After incubation for 1 min., radioactivity also appeared in citrate, aspartate and glutamate. In 12 sec., over 80% of the radioactivity initially incorporated into phosphorylated compounds was present in 3-phosphoglyceric acid; phosphates of glucose, fructose, sedoheptulose and ribose (to a minor extent) became labelled in the later samples. The specific radioactivity of cellular material obtained from cells grown on [C14] formate in air was reduced 17-fold by bubbling air+CO2 (95:5, v/v) through the growing culture. Thus at least 94% of the carbon incorporated must have passed through the stage of CO2 or a compound in ready equilibrium with it. These results show that the organism synthesizes cell constituents from CO2 by a cycle similar to that found in photosynthetic organisms and other autotrophic organisms. The necessary energy is derived from oxidation of the formate to CO2.