This Article Full Text Full Text (PDF) Supplemental material Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Lahmi, R. Articles by Schwarz, R. Search for Related Content PubMed PubMed Citation Articles by Lahmi, R. Articles by Schwarz, R.

 Previous Article  |  Next Article 

Journal of Bacteriology, July 2006, p. 5258-5265, Vol. 188, No. 14
0021-9193/06/$08.00+0     doi:10.1128/JB.00209-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Alanine Dehydrogenase Activity Is Required for Adequate Progression of Phycobilisome Degradation during Nitrogen Starvation in Synechococcus elongatus PCC 7942

The Mina & Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, 52900, Israel,¹ Universität Rostock, Institut Biowissenschaften, Abteilung Pflanzenphysiologie, Albert-Einstein-Str. 3, D-18051 Rostock, Germany,² Institut für Mikrobiologie und Molekularbiologie, Justus-Liebig-Universität Giessen, 35392 Giessen, Germany³

Received 8 February 2006/ Accepted 24 April 2006

Degradation of the cyanobacterial light-harvesting antenna, the phycobilisome, is a general acclimation response that is observed under various stress conditions. In this study we identified a novel mutant of Synechococcus elongatus PCC 7942 that exhibits impaired phycobilisome degradation specifically during nitrogen starvation, unlike previously described mutants, which exhibit aberrant degradation under nitrogen, sulfur, and phosphorus starvation conditions. The phenotype of the new mutant, Ald, results from inactivation of ald (encoding alanine dehydrogenase). Ald is deficient in transcription induction of a number of genes during nitrogen starvation. These genes include the "general nutrient stress-related" genes, nblA and nblC, the products of which are essential for phycobilisome degradation. Furthermore, transcripts of several specific nitrogen-responsive genes accumulate at lower levels in Ald than in the wild-type strain. In contrast, ald inactivation did not decrease the accumulation of transcripts during sulfur starvation. Transcription of ald is induced upon nitrogen starvation, which is consistent with the ability of wild-type cells to maintain a low cellular content of alanine under these conditions. Unlike wild-type cells, Ald accumulates alanine upon nitrogen starvation. Our analyses suggest that alanine dehydrogenase activity is necessary for an adequate cellular response to nitrogen starvation. Decomposition of alanine may be required to provide a sufficient amount of ammonia. Furthermore, the accumulated alanine, or a related metabolite, may interfere with the cues that modulate acclimation during nitrogen starvation. Taken together, our results provide novel information regarding cellular responses to nitrogen starvation and suggest that mechanisms related to nitrogen-specific responses are involved in modulation of a general acclimation process.

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