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Journal of Bacteriology, December 1999, p. 7363-7372, Vol. 181, No. 23
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

A Novel Nitrate/Nitrite Permease in the Marine Cyanobacterium Synechococcus sp. Strain PCC 7002

Toshio Sakamoto, Kaori Inoue-Sakamoto, and Donald A. Bryant*

Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802

Received 27 July 1999/Accepted 16 September 1999

The nrtP and narB genes, encoding nitrate/nitrite permease and nitrate reductase, respectively, were isolated from the marine cyanobacterium Synechococcus sp. strain PCC 7002 and characterized. NrtP is a member of the major facilitator superfamily and is unrelated to the ATP-binding cassette-type nitrate transporters that previously have been described for freshwater strains of cyanobacteria. However, NrtP is similar to the NRT2-type nitrate transporters found in diverse organisms. An nrtP mutant strain consumes nitrate at a 4.5-fold-lower rate than the wild type, and this mutant grew exponentially on a medium containing 12 mM nitrate at a rate approximately 2-fold lower than that of the wild type. The nrtP mutant cells could not consume nitrite as rapidly as the wild type at pH 10, suggesting that NrtP also functions in nitrite uptake. A narB mutant was unable to grow on a medium containing nitrate as a nitrogen source, although this mutant could grow on media containing urea or nitrite with rates similar to those of the wild type. Exogenously added nitrite enhanced the in vivo activity of nitrite reductase in the narB mutant; this suggests that nitrite acts as a positive effector of nitrite reductase. Transcripts of the nrtP and narB genes were detected in cells grown on nitrate but were not detected in cells grown on urea or ammonia. Transcription of the nrtP and narB genes is probably controlled by the NtcA transcription factor for global nitrogen control. The discovery of a nitrate/nitrite permease in Synechococcus sp. strain PCC 7002 suggests that significant differences in nutrient transporters may occur in marine and freshwater cyanobacteria.

* Corresponding author. Mailing address: S-234 Frear Building, Dept. of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802. Phone: (814) 865-1992. Fax: (814) 863-7024. E-mail: dab14{at}psu.edu.

Journal of Bacteriology, December 1999, p. 7363-7372, Vol. 181, No. 23
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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