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Journal of Bacteriology, March 2002, p. 1314-1323, Vol. 184, No. 5
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.5.1314-1323.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Periplasmic Nitrate Reductase (NapABC Enzyme) Supports Anaerobic Respiration by Escherichia coli K-12

*** Valley Stewart,1,2* Yiran Lu,2,{dagger} and Andrew J. Darwin2,{ddagger}

Section of Microbiology, University of California, Davis, California 95616,1 Section of Microbiology, Cornell University, Ithaca, New York 148532

Received 10 September 2001/ Accepted 23 November 2001

Periplasmic nitrate reductase (NapABC enzyme) has been characterized from a variety of proteobacteria, especially Paracoccus pantotrophus. Whole-genome sequencing of Escherichia coli revealed the structural genes napFDAGHBC, which encode NapABC enzyme and associated electron transfer components. E. coli also expresses two membrane-bound proton-translocating nitrate reductases, encoded by the narGHJI and narZYWV operons. We measured reduced viologen-dependent nitrate reductase activity in a series of strains with combinations of nar and nap null alleles. The napF operon-encoded nitrate reductase activity was not sensitive to azide, as shown previously for the P. pantotrophus NapA enzyme. A strain carrying null alleles of narG and narZ grew exponentially on glycerol with nitrate as the respiratory oxidant (anaerobic respiration), whereas a strain also carrying a null allele of napA did not. By contrast, the presence of napA+ had no influence on the more rapid growth of narG+ strains. These results indicate that periplasmic nitrate reductase, like fumarate reductase, can function in anaerobic respiration but does not constitute a site for generating proton motive force. The time course of {Phi}(napF-lacZ) expression during growth in batch culture displayed a complex pattern in response to the dynamic nitrate/nitrite ratio. Our results are consistent with the observation that {Phi}(napF-lacZ) is expressed preferentially at relatively low nitrate concentrations in continuous cultures (H. Wang, C.-P. Tseng, and R. P. Gunsalus, J. Bacteriol. 181:5303-5308, 1999). This finding and other considerations support the hypothesis that NapABC enzyme may function in E. coli when low nitrate concentrations limit the bioenergetic efficiency of nitrate respiration via NarGHI enzyme.

* Corresponding author. Mailing address: Section of Microbiology, University of California, One Shields Ave., Davis, CA 95616-8665. Phone: (530) 754-7994. Fax: (530) 752-9014. E-mail: vjstewart{at}ucdavis.edu.

{dagger} Present address: Program in Pharmacology, Graduate School of Medical Sciences of Cornell University, New York, NY 10021.

{ddagger} Present address: Department of Microbiology, New York University School of Medicine, New York, NY 10016.

Journal of Bacteriology, March 2002, p. 1314-1323, Vol. 184, No. 5
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.5.1314-1323.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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