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Transcription and Regulation of the Bidirectional Hydrogenase in the Cyanobacterium Nostoc sp. Strain PCC 7120
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
2007 (English)In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 73, no 17, 5435-5446 p.Article in journal (Refereed) Published
Abstract [en]

The filamentous, heterocystous cyanobacterium Nostoc sp. strain PCC 7120 (Anabaena sp. strain PCC 7120) possesses an uptake hydrogenase and a bidirectional enzyme, the latter being capable of catalyzing both H2 production and evolution. The completely sequenced genome of Nostoc sp. strain PCC 7120 reveals that the five structural genes encoding the bidirectional hydrogenase (hoxEFUYH) are separated in two clusters at a distance of approximately 8.8 kb. The transcription of the hox genes was examined under nitrogen-fixing conditions, and the results demonstrate that the cluster containing hoxE and hoxF can be transcribed as one polycistronic unit together with the open reading frame alr0750. The second cluster, containing hoxU, hoxY, and hoxH, is transcribed together with alr0763 and alr0765, located between the hox genes. Moreover, alr0760 and alr0761 form an additional larger operon. Nevertheless, Northern blot hybridizations revealed a rather complex transcription pattern in which the different hox genes are expressed differently. Transcriptional start points (TSPs) were identified 66 and 57 bp upstream from the start codon of alr0750 and hoxU, respectively. The transcriptions of the two clusters containing the hox genes are both induced under anaerobic conditions concomitantly with the induction of a higher level of hydrogenase activity. An additional TSP, within the annotated alr0760, 244 bp downstream from the suggested translation start codon, was identified. Electrophoretic mobility shift assays with purified LexA from Nostoc sp. strain PCC 7120 demonstrated specific interactions between the transcriptional regulator and both hox promoter regions. However, when LexA from Synechocystis sp. strain PCC 6803 was used, the purified protein interacted only with the promoter region of the alr0750-hoxE-hoxF operon. A search of the whole Nostoc sp. strain PCC 7120 genome demonstrated the presence of 216 putative LexA binding sites in total, including recA and recF. This indicates that, in addition to the bidirectional hydrogenase gene, a number of other genes, including open reading frames connected to DNA replication, recombination, and repair, may be part of the LexA regulatory network in Nostoc sp. strain PCC 7120.

Place, publisher, year, edition, pages
2007. Vol. 73, no 17, 5435-5446 p.
Keyword [en]
Bacteria, Enzyme, Oxidoreductases, Nostoc, Cyanobacteria, Hydrogenase, Regulation(control), Transcription
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97276DOI: 10.1128/AEM.00756-07ISI: 000249246700006PubMedID: 17630298OAI: oai:DiVA.org:uu-97276DiVA: diva2:172140
Available from: 2008-05-14 Created: 2008-05-14 Last updated: 2011-01-25Bibliographically approved
In thesis
1. Regulation of the Cyanobacterial Bidirectional Hydrogenase
Open this publication in new window or tab >>Regulation of the Cyanobacterial Bidirectional Hydrogenase
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Today, mankind faces a new challenge in energetic terms: a new Industrial Revolution is imperative, already called by some as an Energetic Revolution. This corresponds to a conversion to clean, environmentally friendly and renewable energy sources. In this context, hydrogen arises as a valid alternative, since its combustion produces a considerable amount of energy and releases solely water as a by-product. In the present thesis, two model cyanobacteria, namely Synechocystis sp. strain PCC 6803 and Anabaena/Nostoc sp. strain PCC 7120, were used to examine the hydrogen metabolism. The efforts were focused on to understand the transcription regulation of the hox genes, encoding the structural elements of the bidirectional hydrogenase enzyme. Here, it is shown that such regulation is operated in a very distinct and intricate way, with different factors contributing to its delicate tuning. While in Synechocystis sp. strain PCC 6803 the hox genes were shown to be transcribed as a single operon, in Anabaena/Nostoc sp. strain PCC 7120 they were shown to be transcribed as two independent operons (possibly three). Two transcription factors, LexA and AbrB-like protein, were identified and further characterized in relation to the hydrogen metabolism. Furthermore, different environmental conditions were demonstrated to operate changes on the transcription of the bidirectional hydrogenase genes. In addition, functional studies of three open reading frames found within the hox operon of Synechocystis sp. strain PCC 6803 suggest that this may be a stress responsive operon. However, based on the gained knowledge, it is still not possible to connect the signal transduction pathways, from the environmental signal, through the response regulator, to the final regulation of the hox genes. Nevertheless, the crucial importance of studying the transcription regulation of the different players involved in the hydrogen metabolism is now established and a new era seems to be rising.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 63 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 437
Keyword
Biology, Biohydrogen, Cyanobacteria, Synechocystis, Anabaena/Nostoc, Bidirectional hydrogenase, Transcription regulation, LexA, AbrB-like protein, Biologi
Identifiers
urn:nbn:se:uu:diva-8862 (URN)978-91-554-7215-3 (ISBN)
Public defence
2008-06-05, Å2001, The Ångström Laboratory, Lägerhyddsvägen 1, Polacksbacken,, Uppsala, 10:15 (English)
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Available from: 2008-05-14 Created: 2008-05-14 Last updated: 2009-08-17Bibliographically approved

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Sjöholm, JohannesOliveira, PauloLindblad, Peter

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