Regulation of the ldhA gene, encoding the fermentative lactate dehydrogenase of Escherichia coli

Abstract

The fermentative lactate dehydrogenase (LDH) of Escherichia coli is induced by low pH under anaerobic conditions. Both translational and transcriptional gene fusions to ldhA, which encodes the fermentative LDH, have now been made. Both types of ldhA-lacZ fusion were induced by low pH, but only in the absence of air. However, the translational fusions were consistently expressed at a five-to tenfold higher level than the transcriptional fusions, perhaps implying some post-transcriptional effect on ldhA expression. Introduction of arcB ::Kan decreased expression of both translational and transcriptional ldhA-lacZ fusions by three-to fivefold. Disruption of mlc, which encodes a repressor of several genes of the phosphotransferase system, almost abolished expression of ldhA. Disruption of csrA caused a moderate drop in expression of both operon and protein ldhA fusions, whereas insertional inactivation of csrB or glgA had the opposite effect. These effects are probably indirect, resulting from alterations in sugar accumulation versus storage. Mutations in ptsG, cra, fnr, narL, rpoS, osmZ, appY, ack/pta, aceEF, pfl and ldhA had no effect on expression of the ldhA fusions. ldhA was not induced by the membranepermeant weak acid benzoate, implying that it does not respond to the internal pH directly. Little pH induction was seen during growth on glycerol plus fumarate, suggesting that products of sugar fermentation are necessary for acid induction. Addition of succinate, acetate or lactate had no effect on ldhA expression. In contrast, pyruvate caused a two-to fourfold increase in expression of ldhA-lacZ. This accords with the idea that increased sugar metabolism indirectly induces ldhA.

Escherichia coli Strains Engineered for Homofermentative Production of d -Lactic Acid from Glycerol

“…3 and Table 3), although with slightly lower concentrations of D-lactate produced (10.9 g/ liter). The production of D-lactate in both strains presumably is triggered by an increase in the pyruvate pool, which is known to allosterically activate LDH (15,35).…”

“…1): (i) the disruption of pyruvate-formate lyase (PFL; pflB gene), which catalyzes the conversion of pyruvate to acetyl-CoA and formate, and (ii) the disruption of phosphoacetyltransferase (PTA; pta gene), which converts acetyl-CoA to acetyl-phosphate (first step in acetate production from AcCoA). The increase in lactate accumulation upon the introduction of these mutations appears to be mediated by an increase in the pyruvate pool, as the introduction of defects in pta and pflB do not affect ldhA expression (15). Based on the evidence described above, two platforms for D-lactate production were engineered by using base strains that contain deletions in either the pflB or the pta gene.…”

The ldhA Gene, Encoding Fermentative l -Lactate Dehydrogenase of Corynebacterium glutamicum , Is under the Control of Positive Feedback Regulation Mediated by LldR

“…The ldhA gene is induced in anaerobically grown cultures (3,28). Expression of the ldhA gene is affected both by the redox sensor ArcAB and by carbohydrate metabolism regulators, CsrAB and Mlc (17), although direct binding of the regulators and their regulatory roles involved have not been elucidated. The lldD gene is included in the lldPRD operon (4).…”

RaoN, a small RNA encoded within Salmonella pathogenicity island-11, confers resistance to macrophage-induced stress

“…However, no evidence has yet been found for direct regulation of ldhA expression by RaoN. Since transcription of ldhA is known to be indirectly induced in response to pyruvate (Jiang et al, 2001), we can speculate that the sRNA RaoN may affect some aspects of glucose metabolism, causing an increase in pyruvate concentration.…”