ABSTRACT
Escherichia coli K-12 is able to grow under aerobic conditions on d-malate using DctA for d-malate uptake and the d-malate dehydrogenase DmlA (formerly YeaU) for converting d-malate to pyruvate. Induction of dmlA encoding DmlA required an intact dmlR (formerly yeaT) gene, which encodes DmlR, a LysR-type transcriptional regulator. Induction of dmlA by DmlR required the presence of d-malate or l- or meso-tartrate, but only d-malate supported aerobic growth. The regulator of general C4-dicarboxylate metabolism (DcuS-DcuR two-component system) had some effect on dmlA expression. The anaerobic l-tartrate regulator TtdR or the oxygen sensors ArcB-ArcA and FNR did not have a major effect on dmlA expression. DmlR has a high level of sequence identity (49%) with TtdR, the l- and meso-tartrate-specific regulator of l-tartrate fermentation in E. coli. dmlA was also expressed at high levels under anaerobic conditions, and the bacteria had d-malate dehydrogenase activity. These bacteria, however, were not able to grow on d-malate since the anaerobic pathway for d-malate degradation has a predicted yield of ≤0 ATP/mol d-malate. Slow anaerobic growth on d-malate was observed when glycerol was also provided as an electron donor, and d-malate was used in fumarate respiration. The expression of dmlR is subject to negative autoregulation. The network for regulation and coordination of the central and peripheral pathways for C4-dicarboxylate metabolism by the regulators DcuS-DcuR, DmlR, and TtdR is discussed.