title: Periplasmic nitrate reductase (NapABC enzyme) supports anaerobic respiration by Escherichia coli K-12.
abstract: 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.
authors.affiliation: Section of Microbiology, University of California, O)ne Shields Avenue, Davis, CA 95616-8665, USA. vjstewart@ucdavis.edu
authors.forename: Valley
authors.initials: V
authors.lastname: Stewart
authors.forename: Yiran
authors.initials: Y
authors.lastname: Lu
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Darwin
mesh_terms: D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002244:Carbon / Q000378:metabolism; D003470:Culture Media; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D007700:Kinetics; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000235:genetics / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D010101:Oxygen Consumption; D019897:Periplasm / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D029968:Escherichia coli Proteins; D009566:Nitrates; D009573:Nitrites; D002244:Carbon; D009565:Nitrate Reductases; D050901:Nitrate Reductase; C494404:napA protein, E coli; C494405:narZ protein, E coli