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Journal of Bacteriology, April 2000, p. 1788-1793, Vol. 182, No. 7
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Flavodoxin Mutants of Escherichia coli K-12

Philippe Gaudu and Bernard Weiss*

Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, Georgia 30322

Received 28 October 1999/Accepted 4 January 2000

The flavodoxins are flavin mononucleotide-containing electron transferases. Flavodoxin I has been presumed to be the only flavodoxin of Escherichia coli, and its gene, fldA, is known to belong to the soxRS (superoxide response) oxidative stress regulon. An insertion mutation of fldA was constructed and was lethal under both aerobic and anaerobic conditions; only cells that also had an intact (fldA+) allele could carry it. A second flavodoxin, flavodoxin II, was postulated, based on the sequence of its gene, fldB. Unlike the fldA mutant, an fldB insertion mutant is a viable prototroph in the presence or absence of oxygen. A high-copy-number fldB+ plasmid did not complement the fldA mutation. Therefore, there must be a vital function for which FldB cannot substitute for flavodoxin I. An fldB-lacZ fusion was not induced by H2O2 and is therefore not a member of the oxyR regulon. However, it displayed a soxS-dependent induction by paraquat (methyl viologen), and the fldB gene is preceded by two overlapping regions that resemble known soxS binding sites. The fldB insertion mutant did not have an increased sensitivity to the effects of paraquat on either cellular viability or the expression of a soxS-lacZ fusion. Therefore, fldB is a new member of the soxRS (superoxide response) regulon, a group of genes that is induced primarily by univalent oxidants and redox cycling compounds. However, the reactions in which flavodoxin II participates and its role during oxidative stress are unknown.

* Corresponding author. Mailing address: Glenn Memorial Building, 69 Butler St., S.E., Atlanta, GA 30303. Phone: (404) 616-0602. Fax: (404) 616-7455. E-mail: bweiss2{at}emory.edu.

Journal of Bacteriology, April 2000, p. 1788-1793, Vol. 182, No. 7
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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