The oxidation of acetate by extracts of Micrococcus lysodeikticus.

Evidence has been presented (Saz and Krampitz, 1954) which demonstrates that a-ketoglutarate and citrate are intermediates on the pathway of acetate oxidation by partially lysed cell preparations of Micrococcus lysodeikticu8. Results reported in this publication extend and further substantiate our previous findings. Despite the fact that condensing enzyme can be demonstrated in many aerobic bacteria (Ochoa et al., 1951), most of these organisms oxidize citrate very slowly if at all. The slow rate of citrate utilization has been cited as evidence against the occurrence of the tricarboxylic acid cycle in these organisms. Campbell and Stokes (1951), using dried cell preparations of Pseudomonas fluorescens, presented evidence indicating that this lack of citrate utilization is a result of permeability effects. Stone and Wilson (1952) obtained cell-free extracts of Azotobacter vinelandii which were capable of oxidizing citrate and the other acids of the tricarboxylic acid cycle at a rapid rate. These authors studied the oxidation of acetate-1-C14 by this preparation and demonstrated the incorporation of isotope into citrate, succinate, and a-ketoglutarate. The relative insensitivity of bacterial cells to malonate poisoning has also been cited as an indication against the occurrence of the tricarboxylic acid cycle in bacteria. However, the lack of malonate inhibition in these organisms may also be attributed to the impermeability of the cell wall toward malonate. Extracts of M. lysodeiktics have been obtained which oxidize citrate at a rapid rate and