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Journal of Bacteriology, February 2007, p. 1036-1043, Vol. 189, No. 3
0021-9193/07/$08.00+0     doi:10.1128/JB.01249-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

A Conserved Histidine in Cytochrome c Maturation Permease CcmB of Shewanella putrefaciens Is Required for Anaerobic Growth below a Threshold Standard Redox Potential ^,

Jason R. Dale, Roy Wade Jr., and Thomas J. DiChristina^*

School of Biology, Georgia Institute of Technology, Atlanta, Georgia 30332

Received 8 August 2006/ Accepted 19 November 2006

Shewanella putrefaciens strain 200 respires a wide range of compounds as terminal electron acceptor. The respiratory versatility of Shewanella is attributed in part to a set of c-type cytochromes with widely varying midpoint redox potentials (E'₀). A point mutant of S. putrefaciens, originally designated Urr14 and here renamed CCMB1, was found to grow at wild-type rates on electron acceptors with high E'₀ [O₂, NO₃^–, Fe(III) citrate, MnO₂, and Mn(III) pyrophosphate] yet was severely impaired for growth on electron acceptors with low E'₀ [NO₂^–, U(VI), dimethyl sulfoxide, TMAO (trimethylamine N-oxide), fumarate, -FeOOH, SO₃^2–, and S₂O₃^2–]. Genetic complementation and nucleotide sequence analyses indicated that the CCMB1 respiratory mutant phenotype was due to mutation of a conserved histidine residue (H108Y) in a protein that displayed high homology to Escherichia coli CcmB, the permease subunit of an ABC transporter involved in cytochrome c maturation. Although CCMB1 retained the ability to grow on electron acceptors with high E'₀, the cytochrome content of CCMB1 was <10% of that of the wild-type strain. Periplasmic extracts of CCMB1 contained slightly greater concentrations of the thiol functional group (-SH) than did the wild-type strain, an indication that the E_h of the CCMB1 periplasm was abnormally low. A ccmB deletion mutant was unable to respire anaerobically on any electron acceptor, yet retained aerobic respiratory capability. These results suggest that the mutation of a conserved histidine residue (H108) in CCMB1 alters the redox homeostasis of the periplasm during anaerobic growth on electron acceptors with low (but not high) E'₀. This is the first report of the effects of Ccm deficiencies on bacterial respiration of electron acceptors whose E'₀ nearly span the entire redox continuum.

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* Corresponding author. Mailing address: School of Biology, Georgia Institute of Technology, 310 Ferst Drive, Atlanta, GA 30332-0230. Phone: (404) 894-8419. Fax: (404) 385-4440. E-mail: thomas.dichristina{at}biology.gatech.edu.

Published ahead of print on 1 December 2006.

Supplemental material for this article may be found at http://jb.asm.org/.

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Journal of Bacteriology, February 2007, p. 1036-1043, Vol. 189, No. 3
0021-9193/07/$08.00+0     doi:10.1128/JB.01249-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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