Oxidative Metabolism of Lactate and Acetate by Micrococcus Sodonensis1

Studies on the metabolism of the strict aerobe Micrococcus sodonensis revealed that a considerable accumulation of a-ketoglutarate and glutamate occurred. This accumulation was in evidence, both during growth on complex media and during growth on chemically defined media with acetate as the sole carbon source. The major pathway of terminal respiration in aerobically growing microorganisms appears to be the Krebs tricarboxylic acid cycle. There is much evidence for the presence of a complete tricarboxylic acid cycle in a number of bacteria, including Escherichia coli (Wheat and Ajl, 1954), Micrococcus lysodeikticus (Saz and Krampitz, 1954), and Xanthomonas phaseoli (Madsen and Hochster, 1959). This cycle serves as an effective source of energy for the organism and also provides carbon skeletons for the synthesis of amino acids and other essential metabolites in the cell. An alternate pathway for tricarboxylic acid oxidation has been described (Campbell et al., 1953) in which there is an aldol cleavage of isocitrate to glyoxylate and succinate. This finding, in conjunction with the elucidation of the malate synthetase reaction (Wong and AjI, 1956), resulted in the proposed glyoxylate cycle (Kornberg and Krebs, 1957). This cycle accounts for the requisite synthesis of four carbon units when an organism is utilizing acetate as the sole carbon source. This study is concerned with the metabolism of acetate and lactate and the role of the Krebs and glyoxylate cycles in this organism.