Two members of a network of putative Na+/H+ antiporters are involved in salt and pH tolerance of the freshwater cyanobacterium Synechococcus elongatus.
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 (Deltanha1, Deltanha2, Deltanha3, Deltanha4, Deltanha5, and Deltanha7) had a phenotype different from that of the wild type. In particular, DeltanhA3 cells showed a high-salt- and alkaline-pH-sensitive phenotype, while Deltanha2 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.
Billini
Maria
M
Institute of Biology, National Centre for Scientific Research Demokritos, Aghia Paraskevi, 153 10 Athens, Greece.
Stamatakis
Kostas
K
Sophianopoulou
Vicky
V
D000222:Adaptation, Physiological / Q000187:drug effects; D001426:Bacterial Proteins / Q000145:classification / Q000235:genetics / Q000502:physiology*; D015153:Blotting, Western; D005618:Fresh Water / Q000382:microbiology*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D005816:Genetic Complementation Test; D006863:Hydrogen-Ion Concentration; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012965:Sodium Chloride / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000145:classification / Q000235:genetics / Q000502:physiology*; D046940:Synechococcus / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D017923:Sodium-Hydrogen Exchangers; D012965:Sodium Chloride