The NAR Modulon Systems: Nitrate and Nitrite Regulation of Anaerobic Gene Expression

  • Andrew J. Darwin
  • Valley Stewart


Bacterial survival often depends on the most efficient exploitation of the available resources. This is particularly true for the vital process of energy generation and the enteric bacterium Escherichia coli, with the ability to grow with or without oxygen, has evolved mechanisms to ensure that it takes the most favorable energy-generating option available. This extensively studied organism synthesizes two cytochrome oxidases for respiration at high or low oxygen concentrations. However, when cultivated without aeration the organization of the central metabolic pathways actually typifies that of anaerobes. This is no surprise since the environment of the mammalian intestine is anaerobic. Under these anaerobic conditions the organism generates energy by mixed-acid fermentation and/or by respiration with several terminal electron acceptors. The yield of energy from anaerobic respiration is related to the midpoint potential of the electron acceptor couple.1 The relatively high midpoint potentials of the nitrate/nitrite and nitrite/ammonium couples result in the preference of nitrate and nitrite over the other anaerobic electron acceptors, dimethylsulfoxide (DMSO), trimethylamine N oxide (TMAO) and fumarate. A global regulatory system has evolved to regulate anaerobic gene expression in response to nitrate and nitrite availability.


Nitrate Reductase Gene ExPRESSION Fumarate Reductase Integration Host Factor Null Strain 
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© R.G. Landes Company 1996

Authors and Affiliations

  • Andrew J. Darwin
  • Valley Stewart

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