Abstract
Phototrophic cyanobacteria are limited in growth locations by their need for visible light and must also cope with intermittent ultraviolet radiation (UVR), especially in extreme environments such as deserts and on early Earth. One survival method for cyanobacteria is growing endolithically within minerals such as micas, gypsum, and quartz minerals. However, the capability of different mica minerals to protect cyanobacteria from UVR, while at the same time allowing transmission of photosynthetically active radiation (PAR), has only been minimally examined. In this study, we performed laboratory incubation experiments to demonstrate that a model filamentous cyanobacterium, Leptolyngbya sp., can colonize micas, such as muscovite, phlogopite, and biotite. After inoculation experiments confirmed that these cyanobacteria grew between the sheets of mica, Leptolyngbya sp. colonies were exposed to UVB and UVC for up to 24 hrs, and the level of survival was determined using chlorophyll a and carotenoid assays. Of the three micas investigated, muscovite, being an Fe-poor and Al-rich mica, provided the least attenuation of UVR, however it transmitted the most visible light. Fe-rich biotite provided the best UVR shielding. Phlogopite, apparently because of its intermediate amount of Fe, showed the greatest ability to shield UVR while still transmitting an adequate amount of visible light, making it the ideal habitat for the cyanobacterium. Upon exposure to UVR, significant shifts in several important fatty acids of the cyanobacterium were detected such as linolenic acid and oleic acid, 18:3ω3 and 18:1ω9c, respectively. These cellular changes are interpreted to be a consequence of UVR and other accessory stress (such as O3).
Highlights
IntroductionIn deserts and on early earth, intense ultraviolet radiation (UVR, 280–400 nm in wavelength) can cause various damages to these organisms, such as protein and DNA damage [2], and pigment degradation [3]
Cyanobacteria are found in a number of terrestrial environments [1]
This study suggests that the level of protection is related to the structural Fe content, and of the three micas investigated, phlogopite is most effective in protecting cyanobacteria from ultraviolet radiation (UVR), while still allowing transmission of an adequate amount of visible light for photosynthesis
Summary
In deserts and on early earth, intense ultraviolet radiation (UVR, 280–400 nm in wavelength) can cause various damages to these organisms, such as protein and DNA damage [2], and pigment degradation [3]. Micas as potential UV-resilient habitats for cyanobacteria degraded by UVR but at different rates, with carotenoids generally more resistant than chlorophyll a [4]. To counteract these damaging UVR, cyanobacteria have developed multiple defense mechanisms [5,6,7]. These organisms use UV-screening pigments such as mycosporine-like amino acids and scytonemin. Certain cyanobacterial species can repair damaged DNA and/or turn over proteins to reverse the UVR-induced damage [18]
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