On the redox control of synthesis of anaerobically induced enzymes in enterobacteriaceae

Abstract

Mutants of Escherichia coli were isolated in which transcription of the structural genes for hydrogenase (hyd) and for one of the components of formate dehydrogenase (fdh) (of the formate hydrogen-lyase complex) is coupled with that of the lacZ gene. They were--together with lac fusions of the nifH and nifL genes from Klebsiella--used to study regulation by redox control, of the expression of the respective structural genes. The following results were obtained: (i) beta-galactosidase synthesis was fully repressed in the presence of O2 or nitrate (anaerobically), and induced in the absence of an external electron acceptor. Fumarate as terminal electron acceptor only marginally affected nif expression and partially repressed hyd and fdh expression. Redox control of the synthesis of hydrogenase and formate dehydrogenase, therefore, (as well as that of nif) acts at the level of transcription; the size of the redox potential seems to be correlated with the amount of repression; (ii) beta-galactosidase synthesis in the hyd:: lac and fdh::lac fusion strains is induced by formate. At high concentrations formate reverses the repression by nitrate and fumarate but not that by oxygen.

Cyclic AMP and anaerobic gene expression in E. coli

“…This lends support to the view that the Fnr protein may be redox-sensitive. There is evidence for redox-control of other anaerobicallyinduced enzymes in the enterobacteria [21] and their expression could involve a comparable regulatory mechanism.…”

Isolation and characterization of the Fnr protein, the transcriptional regulator of anaerobic electron transport in Escherichia coli

“…The latter are normally only expressed under anaerobic conditions or at least in the absence of acceptors of higher redox potential, and their expression is affected by the redox potential [29]. This points to the existence of a separate redox control mediated by something other than cyclic AMP, which signals the energy state of the cell [30].…”

Characterization of a fixLJ-regulated Bradyrhizobium japonicum gene sharing similarity with the Escherichia coli fnr and Rhizobium meliloti fixK genes

“…E. coli strains were grown in Luria-Bertani (LB) medium (34); for plasmid selection, it contained the following concentrations of antibiotics: ampicillin, 200 ,ug ml-'; kanamycin, 30 ,ug ml-'; tetracycline, 10 ,ug ml-l. After TnS mutagenesis, recombinant plasmids with Tn5 insertions were selected by applying kanamycin at a concentration of 300 ,ug ml-' in plates. Complementation of E. coli fnr mutant strains was tested either by the ability to restore anaerobic growth on minimal plates containing glycerol and nitrate (51) or by formation of gas from glucose (38).…”