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Microbiology 155 (2009), 25-34; DOI  10.1099/mic.0.022251-0
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Microbiology 155 (2009), 25-34; DOI  10.1099/mic.0.022251-0
© 2009 Society for General Microbiology

Role of calcium in acclimation of the cyanobacterium Synechococcus elongatus PCC 7942 to nitrogen starvation

Francisco Leganés1, Karl Forchhammer2 and Francisca Fernández-Piñas1

1 Departamento de Biología, Universidad Autónoma de Madrid, Madrid 28049, Spain
2 Lehrstuhl für Mikrobiologie-Organismische Interaktionen, Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany

Correspondence
Francisca Fernández-Piñas
francisca.pina{at}uam.es

A Ca2+ signal is required for the process of heterocyst differentiation in the filamentous diazotrophic cyanobacterium Anabaena sp. PCC 7120. This paper presents evidence that a transient increase in intracellular free Ca2+ is also involved in acclimation to nitrogen starvation in the unicellular non-diazotrophic cyanobacterium Synechococcus elongatus PCC 7942. The Ca2+ transient was triggered in response to nitrogen step-down or the addition of 2-oxoglutarate (2-OG), or its analogues 2,2-difluoropentanedioic acid (DFPA) and 2-methylenepentanedioic acid (2-MPA), to cells growing with combined nitrogen, suggesting that an increase in intracellular 2-OG levels precedes the Ca2+ transient. The signalling protein PII and the transcriptional regulator NtcA appear to be needed to trigger the signal. Suppression of the Ca2+ transient by the intracellular Ca2+ chelator N,N'-[1,2-ethanediylbis(oxy-2,1-phenylene)]bis[N-[2-[(acetyloxy)methoxy]-2-oxoethyl]]-,bis[(acetyloxy)methyl] ester (BAPTA-AM) inhibited expression of the glnB and glnN genes, which are involved in acclimation to nitrogen starvation and transcriptionally activated by NtcA. BAPTA-AM treatment partially inhibited expression of the nblA gene, which is involved in phycobiliprotein degradation following nutrient starvation and is regulated by NtcA and NblR; in close agreement, BAPTA-AM treatment partially inhibited bleaching following nitrogen starvation. Taken together, the results presented here strongly suggest an involvement of a defined Ca2+ transient in acclimation of S. elongatus to nitrogen starvation through NtcA-dependent regulation.

Abbreviations: BAPTA-AM, N,N'-[1,2-ethanediylbis(oxy-2,1-phenylene)]bis[N-[2-[(acetyloxy)methoxy]-2-oxoethyl]]-,bis[(acetyloxy)methyl] ester; [Ca2+]i, free intracellular calcium concentration; DFPA, difluoropentanedioic acid; 2-MPA, methylenepentanedioic acid; 2-OG, 2-oxoglutarate






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