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Journal of Bacteriology, May 2004, p. 3224-3229, Vol. 186, No. 10
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.10.3224-3229.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Nitrite-Responsive Activation of the Nitrate Assimilation Operon in Cyanobacteria Plays an Essential Role in Up-Regulation of Nitrate Assimilation Activities under Nitrate-Limited Growth Conditions

Makiko Aichi,1 Shin-Ichi Maeda,2 Kazuhiro Ichikawa,2 and Tatsuo Omata2*

Department of Biological Chemistry, Chubu University, Kasugai 487-8501,1 Laboratory of Molecular Plant Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan2

Received 5 October 2003/ Accepted 6 February 2004

NtcB of the cyanobacterium Synechococcus elongatus strain PCC 7942 is a LysR family protein that enhances expression of the nitrate assimilation operon (nirA operon) in response to the presence of nitrite, an intermediate of assimilatory nitrate reduction. Inactivation of ntcB in this cyanobacterium specifically abolishes the nitrite responsiveness of nirA operon expression, but under nitrate-replete conditions (wherein negative feedback by intracellularly generated ammonium prevails over the positive effect of nitrite) activity levels of the nitrate assimilation enzymes are marginally higher in the wild-type cells than in the mutant cells, raising the issue of whether the nitrite-promoted regulation has physiological importance. On the other hand, the strains carrying ntcB expressed much higher nitrate assimilation enzyme activities under nitrate-limited growth conditions than under nitrate-replete conditions whereas the ntcB-deficient strains showed levels of the enzyme activities lower than those seen under the nitrate-replete conditions. Although the ntcB mutant maintained a constant cell population in a nitrate-limited chemostat when grown as a single culture, it was diluted at a rate expected for nondividing cells when mixed with the wild-type cells and subjected to nitrate limitation in the chemostat culture system. These results demonstrated that the nitrite-promoted activation of the nitrate assimilation operon is essential for up-regulation of the nitrate assimilation activities under the conditions of nitrate limitation and for competitive utilization of nitrate.

* Corresponding author. Mailing address: Laboratory of Molecular Plant Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan. Phone: 81-52-789-4106. Fax: 81-52-789-4107. E-mail: omata{at}agr.nagoya-u.ac.jp.

Journal of Bacteriology, May 2004, p. 3224-3229, Vol. 186, No. 10
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.10.3224-3229.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Espinosa, J., Forchhammer, K., Contreras, A. (2007). Role of the Synechococcus PCC 7942 nitrogen regulator protein PipX in NtcA-controlled processes. Microbiology 153: 711-718 [Abstract] [Full Text]  
  • Tsujimoto, R., Yamazaki, H., Maeda, S.-i., Omata, T. (2007). Distinct Roles of Nitrate and Nitrite in Regulation of Expression of the Nitrate Transport Genes in the Moss Physcomitrella patens. Plant Cell Physiol 48: 484-497 [Abstract] [Full Text]  


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