SCYTONEMIN, A CYANOBACTERIAL SHEATH PIGMENT, PROTECTS AGAINST UVC RADIATION: IMPLICATIONS FOR EARLY PHOTOSYNTHETIC LIFE

During the Precambrian, ultraviolet (UV) radiation reaching the Earth’s surface, including UVC wavelengths (190–280 nm), was considerably higher than present because of the lack of absorbing gases (e.g. O2 and O3) in the atmosphere. High UV flux would have been damaging to photosynthetic organisms e...

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Bibliographic Details
Published in:Journal of phycology 1999-08, Vol.35 (4), p.673-681
Main Authors: Dillon, Jesse G., Castenholz, Richard W.
Format: Article
Language:English
Subjects:
Brackish
Calothrix
Chroococcidiopsis
cyanobacteria
Cyanophyta
Freshwater
Marine
photosynthesis
Precambrian
scytonemin
UVC radiation
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Summary:During the Precambrian, ultraviolet (UV) radiation reaching the Earth’s surface, including UVC wavelengths (190–280 nm), was considerably higher than present because of the lack of absorbing gases (e.g. O2 and O3) in the atmosphere. High UV flux would have been damaging to photosynthetic organisms exposed to solar radiation. Nevertheless, fossil evidence indicates that cyanobacteria‐like ancestors may have evolved as early as 3.5 × 109 yr ago, and were common in shallow marine habitats by 2.5 × 109 years ago. Scytonemin, a cyanobacterial extracellular sheath pigment, strongly absorbs UVC radiation. Exposure to high‐irradiance conditions caused cells to synthesize scytonemin and resulted in decreased UVC inhibition of photosynthetic carbon uptake. It was further demonstrated that scytonemin alone was sufficient for substantial protection against UVC damage. This represents the first experimental demonstration of biological protection against UVC radiation in cyanobacteria. These results suggest that scytonemin may have evolved during the Precambrian and allowed colonization of exposed, shallow‐water and terrestrial habitats by cyanobacteria or their oxygenic ancestors.
ISSN:0022-3646
1529-8817
DOI:10.1046/j.1529-8817.1999.3540673.x