The gram-negative anaerobe Oxalobacter formigenes, grows on oxalate as the principal carbon and energy source, but a small amount of acetate is also required for growth. Experiments were conducted to determine the distribution and the position of label in cellular amino acids from cells grown on [¹³C]oxalate, [¹³C]acetate (1-¹³C, 2-¹³C, and U-¹³C), and ¹³CCO₃. The labeling pattern (determined with NMR spectroscopy) of amino acids was consistent with their formation through common biosynthetic pathways. The majority of the carbons in the amino acids that are usually derived from pyruvate, oxaloacetate, α-ketoglutarate, 3-phosphoglycerate, and carbon in the aromatic amino acids were labeled by oxalate. Carbon from ¹³CO₃ was assimilated primarily into amino acids expected to be derived from oxaloacetate and α-ketoglutarate. Approximately 60% of the acetate that was assimilated into amino acids was incorporated as a C₂ unit into proline, arginine, glutamate, and leucine. The pattern of labeling from acetate in glutamate, arginine, and proline was consistent with acetate incorporation via citrate (si)-synthase and subsequent formation of α-ketoglutarate via the first third of the tricarboxylic acid pathway. Acetate was also assimilated into amino acids derived from pyruvate and oxaloacetate, but results indicated that this incorporation was as single carbon atoms. Based on these findings, cell-free extracts were assayed for several key biosynthetic enzymes. Enzymatic activities found included glutamate dehydrogenase, phosphoenolpyruvate carboxylase, and pyruvate carboxylase. These findings are consistent with proposed biosynthetic mechanisms.

Oxalobacterformigenes is the only well-documented oxalate-degrading bacterium isolated from the gastrointestinal tract of animals. The production of ATP by Oxalobacter formigenes is centered around oxalate metabolism and oxalate is required for growth. A small amount of acetate (0.5 mM) is also required. Oxalate is decarboxylated to formate plus CO₂ in nearly equimolar amounts. Experiments were conducted to determine which potential carbon sources (oxalate, acetate, formate, CO₂) were assimilated by Oxalobacter formigenes and which metabolic pathways were operative in carbon assimilation. Measurements of the specific activities of total cell carbon after growth with different ¹⁴C-labeled precursors indicated that at least 54% of the total cell carbon was derived from oxalate and at least 7% was derived from acetate. Carbonate was also assimilated, but formate was not a significant source of cell carbon. Labeling patterns in amino acids from cells grown in [¹⁴C]oxalate or ¹⁴CO₃ were different; however, in both cases ¹⁴C was widely distributed into most cellular amino acids. Carbon from [¹⁴C]acetate was less widely distributed and detected mainly in those amino acids known to be derived from α-ketoglutarate, oxaloacetate, and pyruvate. Cell-free extracts contained citrate synthase, isocitrate dehydrogenase, and malate dehydrogenase activities. The labeling observed in amino acids derived from acetate is in agreement with the function of these enzymes in biosynthesis and indicates that the majority of acetate carbon entered into amino acid biosynthesis via well-known pathways.