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Journal of Bacteriology, May 2009, p. 3265-3272, Vol. 191, No. 10
0021-9193/09/$08.00+0     doi:10.1128/JB.00013-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Nitrite Transport Activity of the ABC-Type Cyanate Transporter of the Cyanobacterium Synechococcus elongatus{triangledown}

Shin-ichi Maeda* and Tatsuo Omata

Laboratory of Molecular Plant Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan

Received 6 January 2009/ Accepted 5 March 2009

In addition to the ATP-binding cassette (ABC)-type nitrate/nitrite-bispecific transporter, which has a high affinity for both substrates (Km, ~1 µM), Synechococcus elongatus has an active nitrite transport system with an apparent Km (NO2–) value of 20 µM. We found that this activity depends on the cynABD genes, which encode a putative cyanate (NCO–) ABC-type transporter. Accordingly, nitrite transport by CynABD was competitively inhibited by NCO– with a Ki value of 0.025 µM. The transporter was induced under conditions of nitrogen deficiency, and the induced cells showed a Vmax value of 11 to 13 µmol/mg of chlorophyll per h for cyanate or nitrite, which could supply ~30% of the amount of nitrogen required for optimum growth. Its relative specificity for the substrates and regulation at transcriptional and posttranslational levels suggested that the physiological role of the bispecific cyanate/nitrite transporter in S. elongatus is to allow nitrogen-deficient cells to assimilate low concentrations of cyanate in the medium. Its contribution to nitrite assimilation was significant in a mutant lacking the ABC-type nitrate/nitrite transporter, suggesting a possible role for CynABD in nitrite assimilation by cyanobacterial species that lack another high-affinity mechanism(s) for nitrite transport.

* Corresponding author. Mailing address: Laboratory of Molecular Plant Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan. Phone: 81-52-789-4104. Fax: 81-52-789-4107. E mail: maeda{at}agr.nagoya-u.ac.jp

{triangledown} Published ahead of print on 13 March 2009.

Journal of Bacteriology, May 2009, p. 3265-3272, Vol. 191, No. 10
0021-9193/09/$08.00+0     doi:10.1128/JB.00013-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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