Regulation of Aerobic and Anaerobic d -Malate Metabolism of Escherichia coli by the LysR-Type Regulator DmlR (YeaT)

Abstract

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 C 4 -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 C 4 -dicarboxylate metabolism by the regulators DcuS-DcuR, DmlR, and TtdR is discussed.