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TRANSCRIPTIONAL ANALYSIS OF THE UNICELLULAR, DIAZOTROPHIC CYANOBACTERIUM CYANOTHECE SP. ATCC 51142 GROWN UNDER SHORT DAY/NIGHT CYCLES1

Authors

  • Jo¨rg Toepel,

    1. Department of Biological Sciences, Purdue University, 201 S. University Street, West Lafayette, Indiana 47907, USA
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  • Jason E. McDermott,

    1. Computational Biology & Bioinformatics Group, Pacific Northwest National Laboratory (PNNL), Richland, Washington 99352, USA
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  • Tina C. Summerfield,

    1. Department of Biological Sciences, Purdue University, 201 S. University Street, West Lafayette, Indiana 47907, USA
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    • 2

      Present address: Department of Biochemistry, University of Otago, PO Box 56, Dunedin, New Zealand.

  • Louis A. Sherman

    1. Department of Biological Sciences, Purdue University, 201 S. University Street, West Lafayette, Indiana 47907, USA
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  • 1

    Received 22 August 2008. Accepted 26 January 2009.

Abstract

Cyanothece sp. strain ATCC 51142 is a unicellular, diazotrophic cyanobacterium that demonstrates extensive metabolic periodicities of photosynthesis, respiration, and nitrogen fixation when grown under N2-fixing conditions. We have performed a global transcription analysis of this organism using 6 h light:dark (L:D) cycles in order to determine the response of the cell to these conditions and to differentiate between diurnal and circadian-regulated genes. In addition, we used a context-likelihood of relatedness (CLR) analysis with these data and those from 2 d L:D and L:D plus continuous light experiments to better differentiate between diurnal and circadian-regulated genes. Cyanothece sp. acclimated in several ways to growth under short L:D conditions. Nitrogen was fixed in every second dark period and only once in each 24 h period. Nitrogen fixation was strongly correlated to the energy status of the cells and glycogen breakdown, and high respiration rates were necessary to provide appropriate energy and anoxic conditions for this process. We conclude that glycogen breakdown is a key regulatory step within these complex processes. Our results demonstrated that the main metabolic genes involved in photosynthesis, respiration, nitrogen fixation, and central carbohydrate metabolism have strong (or total) circadian-regulated components. The short L:D cycles enable us to identify transcriptional differences among the family of psbA genes, as well as the differing patterns of the hup genes, which follow the same pattern as nitrogenase genes, relative to the hox genes, which displayed a diurnal, dark-dependent gene expression.

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