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Applied and Environmental Microbiology, May 2007, p. 3028-3033, Vol. 73, No. 9
0099-2240/07/$08.00+0     doi:10.1128/AEM.02606-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Lack of Control of Nitrite Assimilation by Ammonium in an Oceanic Picocyanobacterium, Synechococcus sp. Strain WH 8103{triangledown}

Michael Wyman* and Clare Bird

School of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, United Kingdom

Received 8 November 2006/ Accepted 23 February 2007

In cyanobacteria, the transcriptional activator NtcA is involved in global nitrogen control and, in the absence of ammonium, regulates the expression of genes involved in the assimilation of alternative nitrogen sources. The oceanic picocyanobacterium Synechococcus sp. strain WH 8103 harbors a copy of ntcA, but in the present study, we show that unlike other marine cyanobacteria that have been investigated, this strain is capable of coassimilating nitrite when grown in the presence of ammonium. Transcript levels for the genes encoding the nitrate/nitrite-bispecific permease NrtP and nitrate reductase (NarB) were substantially down-regulated by ammonium, whereas the abundances of nitrite reductase (NirA) transcripts were similar in nitrite- and ammonium-grown cells. The growth of Synechococcus sp. strain WH 8103 in medium containing both ammonium and nitrite resulted in only minor changes in the expression profile in comparison to that of nitrite-grown cells with the exception that the gene encoding the high-affinity ammonium transporter Amt1 was down-regulated to the levels seen in ammonium-grown cells. Whereas the expression of nrtP, narB, and amt1 appears to be NtcA dependent in this marine cyanobacterium, the transcription and expression of nirA appear not to be. The ability to coassimilate nitrite and reduced-nitrogen sources like ammonium may be an adaptive trait that enables oceanic strains like Synechococcus sp. strain WH 8103 to exploit the low nitrite concentrations found in oceanic surface waters that are not available to their principal and more numerous competitor, Prochlorococcus.

* Corresponding author. Mailing address: School of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, United Kingdom. Phone: 44 (0)1786 467784. Fax: 44 (0)1786 464994. E-mail: mw4{at}stir.ac.uk

{triangledown} Published ahead of print on 2 March 2007.

Applied and Environmental Microbiology, May 2007, p. 3028-3033, Vol. 73, No. 9
0099-2240/07/$08.00+0     doi:10.1128/AEM.02606-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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