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Journal of Bacteriology, November 2006, p. 7796-7806, Vol. 188, No. 22
0021-9193/06/$08.00+0     doi:10.1128/JB.01097-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Genome-Wide Analysis of Light Sensing in Prochlorococcus ^,

Claudia Steglich,^1, Matthias Futschik,² Trent Rector,³ Robert Steen,³ and Sallie W. Chisholm^1*

Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139,¹ Humboldt University, Institute of Theoretical Biology, Invalidenstr. 43, D-10115 Berlin, Germany,² Harvard Medical School, Department of Genetics, Biopolymers Facility, 77 Avenue Louis Pasteur, Boston, Massachusetts 02115³

Received 24 July 2006/ Accepted 28 August 2006

Prochlorococcus MED4 has, with a total of only 1,716 annotated protein-coding genes, the most compact genome of a free-living photoautotroph. Although light quality and quantity play an important role in regulating the growth rate of this organism in its natural habitat, the majority of known light-sensing proteins are absent from its genome. To explore the potential for light sensing in this phototroph, we measured its global gene expression pattern in response to different light qualities and quantities by using high-density Affymetrix microarrays. Though seven different conditions were tested, only blue light elicited a strong response. In addition, hierarchical clustering revealed that the responses to high white light and blue light were very similar and different from that of the lower-intensity white light, suggesting that the actual sensing of high light is mediated via a blue-light receptor. Bacterial cryptochromes seem to be good candidates for the blue-light sensors. The existence of a signaling pathway for the redox state of the photosynthetic electron transport chain was suggested by the presence of genes that responded similarly to red and blue light as well as genes that responded to the addition of DCMU [3-(3,4-dichlorophenyl)-1,1-N-N'-dimethylurea], a specific inhibitor of photosystem II-mediated electron transport.

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* Corresponding author. Mailing address: Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139. Phone: (617) 253-1771. Fax: (617) 258-7009. E-mail: chisholm{at}mit.edu.

Published ahead of print on 15 September 2006.

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

Present address: University Freiburg, Department of Biology II/Experimental Bioinformatics, Schaenzlestr. 1, D-79104 Freiburg, Germany.

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Journal of Bacteriology, November 2006, p. 7796-7806, Vol. 188, No. 22
0021-9193/06/$08.00+0     doi:10.1128/JB.01097-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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