ASSIMILATION OF OXALATE, ACETATE, AND CO2 BY OXALOBACTER-FORMIGENES

Oxalobacter-formigenes is the only well-documented oxalate-degrading b acterium isolated from the gastrointestinal tract of animals. The prod uction of ATP by Oxalobacter formigenes is centered around oxalate met abolism and oxalate is required for growth. A small amount of acetate (0.5 mM) is also required. Oxalate is decarboxylated to formate plus C O2 in nearly equimolar amounts. Experiments were conducted to determin e which potential carbon sources (oxalate, acetate, formate, CO2) were assimilated by Oxalobacter formigenes and which metabolic pathways we re operative in carbon assimilation. Measurements of the specific acti vities of total cell carbon after growth with different C-14-labeled p recursors indicated that at least 54% of the total cell carbon was der ived 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 [C-14]ox alate or (CO3)-C-14 were different; however, in both cases C-14 was wi dely distributed into most cellular amino acids. Carbon from [C-14]ace tate was less widely distributed and detected mainly in those amino ac ids known to be derived from alpha-ketoglutarate, oxaloacetate, and py ruvate. Cell-free extracts contained citrate synthase, isocitrate dehy drogenase, 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 ac etate carbon entered into amino acid biosynthesis via well-known pathw ays.