EVIDENCE FOR AN ULTRAVIOLET SUNSCREEN ROLE OF THE EXTRACELLULAR PIGMENT SCYTONEMIN IN THE TERRESTRIAL CYANOBACTERIUM Chiorogloeopsis sp.

Abstract

The proposed photoprotective role of the UV-A absorbing, extracellular pigment scytonemin was studied in the terrestrial cyanobacterium Chlorogloeopsis sp. strain O-89-Cgs(1). UV-A (315-400 nm) caused growth delay, cell growth restarting only when scytonemin had accumulated in the extracellular envelopes. Cultures with scytonemin were more resistant to photoinhibition of photosynthesis than cultures without scytonemin, the differential resistance being much greater to UV-A-caused photoinhibition than to photoinhibition caused by visible light. The presence of scytonemin in the extracellular envelopes was correlated with the inability of UV-A radiation to induce strong photopigment fluorescence (685 nm emission), regardless of the specific content os photosynthetic pigments. The physical removal of the scytonemin containing extracellular envelopes brought about the loss of UV-A resistance as measured by photobleaching rates of chlorophyll a under conditions of physiological inactivity (desiccation). These observations provide strong evidence for the proposed protective role of scytonemin, as a passive UV-A sunscreen, in cyanobacteria.

Effects of UV radiation on five marine microphytobenthic Wadden sea diatoms, isolated from the Solthörn tidal flat (Lower Saxony, southern North Sea) – Part II: changes in carbohydrate, amino acid and fatty acid composition

“…Besides others, the relative increase of short-chained fatty acids and a decrease of polyunsaturated fatty acids (PUFAs) are described as common responses in UV-stressed phytoplankton cells (e.g. Garcia-Pichel et al, 1992). Our data suggest that the impact of UV depends on the quality of the irradiance.…”

Isolate-specific effects of ultraviolet radiation on photosynthesis, growth and mycosporine-like amino acids in the microbial mat-forming cyanobacterium Microcoleus chthonoplastes

“…Another protective mechanism against enhanced UV-B is the biosynthesis and accumulation of sunscreen compounds like the yellow-brown lipid-soluble scytonemin that occurs predominantly in the extracellular sheaths of cyanobacteria playing an eminent role in preventing UVinduced photodamage (Garcia-Pichel et al 1992). Caroteniods, which are concentrated mainly in thylakoid membrane, cell membranes, and cell walls of cyanobacteria, also protect cells from lethal eVect of photooxidation by singlet oxygen (Edge et al 1997;Kerfeld 2004).…”

Synergistic allelochemicals from a freshwater cyanobacterium

“…However, in general the ecological role played by the majority of these metabolites is not well known (6,7). Functions established to date for cyanobacterial secondary metabolites include nitrogen storage (8), UV protection (9), metal chelation (10), defense against predation (11), and quorum sensing (12).…”