Selection for citrate synthase deficiency in icd mutants of Escherichia coli

Lakshmi, T. Mohana; Helling, Robert B.

doi:10.1128/jb.127.1.76-83.1976

Cited by 51 publications

(23 citation statements)

References 13 publications

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“…A higher value has been reported for purified E. coli aconitase, 3 ϫ 10 7 M Ϫ1 s Ϫ1 (29). In all studies, the inactivation rates were lowered somewhat by the presence of substrate (14,20), which partially shields the active site; this might particularly affect aconitase, since substrate more effectively protects aconitase and since citrate levels may be saturating in vivo (20,42,49). Based on the values determined by Flint, we use 3 ϫ 10 6 M Ϫ1 s Ϫ1 as a representative value for the inactivation rate constants (k inactivation ) of the dehydratases in the following equation:…”

Section: Discussionmentioning

confidence: 99%

Balance between Endogenous Superoxide Stress and Antioxidant Defenses

1998

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Cells devoid of cytosolic superoxide dismutase (SOD) suffer enzyme inactivation, growth deficiencies, and DNA damage. It has been proposed that the scant superoxide (O2 −) generated by aerobic metabolism harms even cells that contain abundant SOD. However, this idea has been difficult to test. To determine the amount of O2 − that is needed to cause these defects, we modulated the O2 − concentration insideEscherichia coli by controlling the expression of SOD. An increase in O2 − of more than twofold above wild-type levels substantially diminished the activity of labile dehydratases, an increase in O2 − of any more than fourfold measurably impaired growth, and a fivefold increase in O2 − sensitized cells to DNA damage. These results indicate that E. coli constitutively synthesizes just enough SOD to defend biomolecules against endogenous O2 − so that modest increases in O2 − concentration diminish cell fitness. This conclusion is in excellent agreement with quantitative predictions based upon previously determined rates of intracellular O2 − production, O2 −dismutation, dehydratase inactivation, and enzyme repair. The vulnerability of bacteria to increased intracellular O2 − explains the widespread use of superoxide-producing drugs as bactericidal weapons in nature. E. coli responds to such drugs by inducing the SoxRS regulon, which positively regulates synthesis of SOD and other defensive proteins. However, even toxic amounts of endogenous O2 −did not activate SoxR, and SoxR activation by paraquat was not at all inhibited by excess SOD. Therefore, in responding to redox-cycling drugs, SoxR senses some signal other than O2 −.

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Section: Discussionmentioning

confidence: 99%

Balance between Endogenous Superoxide Stress and Antioxidant Defenses

1998

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“…Attempts to obtain spontaneous revertants or genetic recombinants of strain "I'200 capable of growth without an added source of c~-ketoglutarate iaave thus far given negative results. It is of interest that secondary mutants with faster growth rates appear spontaneously in Eseherichga coff strains lacking ICD activity [11]; it seems that accumulation of an inhibitory compound is prevented by a second lesion that ellmiriates CS activity in such mutants. This explanation, however, does not readily account for faster growing secondary mutants ~af R. capsulata WE29 since this strain lac~ both CS aad ICD activities initially.…”

Section: Other Observations and Remarksmentioning

confidence: 99%

Nitrogen assimilation defects in a mutant of Rhodopseudomonas capsulata blocked in α-ketoglutarate generation

Beatty¹

1977

FEMS Microbiology Letters

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“…A mutant strain with deletions of both citrate synthase genes (citA and citZ) and of citC had a phenotype very similar to that of the citZC deletion strain (data not shown). Reduction of citrate synthase activity also serves to cure in part the growth defect of an ICDH mutant of E. coli (31).…”

Section: Resultsmentioning

confidence: 99%

Metabolic Imbalance and Sporulation in an Isocitrate Dehydrogenase Mutant of Bacillus subtilis

et al. 1999

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A Bacillus subtilis mutant with a deletion in thecitC gene, encoding isocitrate dehydrogenase, the third enzyme of the tricarboxylic acid branch of the Krebs cycle, exhibited reduced growth yield in broth medium and had greatly reduced ability to sporulate compared to the wild type due to a block at stage I, i.e., a failure to form the polar division septum. In early stationary phase, mutant cells accumulated intracellular and extracellular concentrations of citrate and isocitrate that were at least 15-fold higher than in wild-type cells. The growth and sporulation defects of the mutant could be partially bypassed by deletion of the major citrate synthase gene (citZ), by raising the pH of the medium, or by supplementation of the medium with certain divalent cations, suggesting that abnormal accumulation of citrate affects survival of stationary-phase cells and sporulation by lowering extracellular pH and chelating metal ions. While these genetic and environmental alterations were not sufficient to allow the majority of the mutant cell population to pass the stage I block (lack of asymmetric septum formation), introduction of the sof-1 mutant form of the Spo0A transcription factor, when coupled with a reduction in citrate synthesis, restored sporulation gene expression and spore formation nearly to wild-type levels. Thus, the primary factor inhibiting sporulation in a citC mutant is abnormally high accumulation of citrate, but relief of this metabolic defect is not by itself sufficient to restore competence for sporulation.

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Selection for citrate synthase deficiency in icd mutants of Escherichia coli

Cited by 51 publications

References 13 publications

Balance between Endogenous Superoxide Stress and Antioxidant Defenses

Balance between Endogenous Superoxide Stress and Antioxidant Defenses

Nitrogen assimilation defects in a mutant of Rhodopseudomonas capsulata blocked in α-ketoglutarate generation

Metabolic Imbalance and Sporulation in an Isocitrate Dehydrogenase Mutant of Bacillus subtilis

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