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Journal of Bacteriology, October 2008, p. 6318-6329, Vol. 190, No. 19
0021-9193/08/$08.00+0     doi:10.1128/JB.00696-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Two Members of a Network of Putative Na+/H+ Antiporters Are Involved in Salt and pH Tolerance of the Freshwater Cyanobacterium Synechococcus elongatus{triangledown} ,{dagger}

Maria Billini, Kostas Stamatakis, and Vicky Sophianopoulou*

Institute of Biology, National Centre for Scientific Research "Demokritos" (NCSRD), Aghia Paraskevi, 153 10 Athens, Greece

Received 16 May 2008/ Accepted 11 July 2008

Synechococcus elongatus strain PCC 7942 is an alkaliphilic cyanobacterium that tolerates a relatively high salt concentration as a freshwater microorganism. Its genome sequence revealed seven genes, nha1 to nha7 (syn_pcc79420811, syn_pcc79421264, syn_pcc7942359, syn_pcc79420546, syn_pcc79420307, syn_pcc79422394, and syn_pcc79422186), and the deduced amino acid sequences encoded by these genes are similar to those of Na+/H+ antiporters. The present work focused on molecular and functional characterization of these nha genes encoding Na+/H+ antiporters. Our results show that of the nha genes expressed in Escherichia coli, only nha3 complemented the deficient Na+/H+ antiporter activity of the Na+-sensitive TO114 recipient strain. Moreover, two of the cyanobacterial strains with separate disruptions in the nha genes ({Delta}nha1, {Delta}nha2, {Delta}nha3, {Delta}nha4, {Delta}nha5, and {Delta}nha7) had a phenotype different from that of the wild type. In particular, {Delta}nhA3 cells showed a high-salt- and alkaline-pH-sensitive phenotype, while {Delta}nha2 cells showed low salt and alkaline pH sensitivity. Finally, the transcriptional profile of the nha1 to nha7 genes, monitored using the real-time PCR technique, revealed that the nha6 gene is upregulated and the nha1 gene is downregulated under certain environmental conditions.

* Corresponding author. Mailing address: Institute of Biology, National Centre for Scientific Research "Demokritos" (NCSRD), Aghia Paraskevi, 153 10 Athens, Greece. Phone: (30) 2106503563. Fax: (30) 2106511767. E-mail: vicky{at}bio.demokritos.gr

{triangledown} Published ahead of print on 18 July 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, October 2008, p. 6318-6329, Vol. 190, No. 19
0021-9193/08/$08.00+0     doi:10.1128/JB.00696-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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