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Applied and Environmental Microbiology, July 2009, p. 4861-4869, Vol. 75, No. 14
0099-2240/09/$08.00+0     doi:10.1128/AEM.02508-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Organization, Evolution, and Expression Analysis of the Biosynthetic Gene Cluster for Scytonemin, a Cyanobacterial UV-Absorbing Pigment{triangledown} ,{dagger}

Carla M. Sorrels,1 Philip J. Proteau,2 and William H. Gerwick1,3*

Center for Marine Biomedicine and Biotechnology, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California,1 College of Pharmacy, Oregon State University, Corvallis, Oregon,2 Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California3

Received 1 November 2008/ Accepted 26 May 2009

Cyanobacteria are photosynthetic prokaryotes capable of protecting themselves from UV radiation through the biosynthesis of UV-absorbing secondary metabolites, such as the mycosporines and scytonemin. Scytonemin, a novel indolic-phenolic pigment, is found sequestered in the sheath, where it provides protection to the subtending cells during exposure to UV radiation. The biosynthesis of scytonemin is encoded by a previously identified gene cluster that is present in six cyanobacterial species whose genomes are available. A comparison of these clusters reveals that two major cluster architectures exist which appear to have evolved through rearrangements of large sections, such as those genes responsible for aromatic amino acid biosynthesis and through the insertion of genes that potentially confer additional biosynthetic capabilities. Differential transcriptional expression analysis demonstrated that the entire gene cluster is transcribed in higher abundance after exposure to UV radiation. This analysis helps delineate the cluster boundaries and indicates that regulation of this cluster is controlled by the presence or absence of UV radiation. The findings from an evolutionary phylogenetic analysis combined with the fact that the scytonemin gene cluster is distributed across several cyanobacterial lineages led to our proposal that the distribution of this gene cluster is best explained through an ancient evolutionary origin.

* Corresponding author. Mailing address: Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, MC0212, La Jolla, CA 92093-0212. Phone: (858) 534-0578. Fax: (858) 534-0529. E-mail: wgerwick{at}ucsd.edu

{triangledown} Published ahead of print on 29 May 2009.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, July 2009, p. 4861-4869, Vol. 75, No. 14
0099-2240/09/$08.00+0     doi:10.1128/AEM.02508-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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