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RESEARCH PRODUCT

C 4 -Dicarboxylate Utilization in Aerobic and Anaerobic Growth

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description

C 4 -dicarboxylates and the C 4 -dicarboxylic amino acid l -aspartate support aerobic and anaerobic growth of Escherichia coli and related bacteria. In aerobic growth, succinate, fumarate, D - and L -malate, L -aspartate, and L -tartrate are metabolized by the citric acid cycle and associated reactions. Because of the interruption of the citric acid cycle under anaerobic conditions, anaerobic metabolism of C 4 -dicarboxylates depends on fumarate reduction to succinate (fumarate respiration). In some related bacteria (e.g., Klebsiella ), utilization of C 4 -dicarboxylates, such as tartrate, is independent of fumarate respiration and uses a Na + -dependent membrane-bound oxaloacetate decarboxylase. Uptake of the C 4 -dicarboxylates into the bacteria (and anaerobic export of succinate) is achieved under aerobic and anaerobic conditions by different sets of secondary transporters. Expression of the genes for C 4 -dicarboxylate metabolism is induced in the presence of external C 4 -dicarboxylates by the membrane-bound DcuS-DcuR two-component system. Noncommon C 4 -dicarboxylates like l -tartrate or D -malate are perceived by cytoplasmic one-component sensors/transcriptional regulators. This article describes the pathways of aerobic and anaerobic C 4 -dicarboxylate metabolism and their regulation. The citric acid cycle, fumarate respiration, and fumarate reductase are covered in other articles and discussed here only in the context of C 4 -dicarboxylate metabolism. Recent aspects of C 4 -dicarboxylate metabolism like transport, sensing, and regulation will be treated in more detail. This article is an updated version of an article published in 2004 in EcoSal Plus . The update includes new literature, but, in particular, the sections on the metabolism of noncommon C 4 -dicarboxylates and their regulation, on the DcuS-DcuR regulatory system, and on succinate production by engineered E. coli are largely revised or new.