C 4 -Dicarboxylate Degradation in Aerobic and Anaerobic Growth

Abstract

C 4 -dicarboxylates, like succinate, fumarate, L - and D -malate, tartrate, and the C 4 -dicarboxylic amino acid aspartate, support aerobic and anaerobic growth of Escherichia coli and related bacteria and can serve as carbon and energy sources. In aerobic growth, the C 4 -dicarboxylates are oxidized in the citric acid cycle. Due to the interruption of the citric acid cycle under anaerobic conditions, anaerobic metabolism of the C 4 -dicarboxylates depends on fumarate reduction to succinate. In some related bacteria (e.g., Klebsiella ), degradation of C 4 -dicarboxylates, like tartrate, uses a different mechanism and pathway. It requires the functioning of an Na + -dependent and membrane-associated oxaloacetate decarboxylase. Due to the incomplete function of the citric acid cycle in anaerobic growth, succinate supports only aerobic growth of E. coli . This chapter describes the pathways of and differences in aerobic and anaerobic C 4 -dicarboxylate metabolism and the physiological consequences. The citric acid cycle, fumarate respiration, and fumarate reductase are discussed here only in the context of aerobic and anaerobic C 4 -dicarboxylate metabolism. Some recent aspects of C 4 -dicarboxylate metabolism, such as transport and sensing of C 4 -dicarboxylates, and their relationships are treated in more detail.