How do ciliates protect themselves from ultraviolet radiation?
Recently, we identified several photoprotective strategies in ciliates from lakes (in cooperation with the ‚Lake and Glacier Research Group’ of the Institute of Ecology at the University of Innsbruck):
Living in symbiosis
Some ciliate species live in symbiosis together with unicellular algae (mixotrophy). The algae do not only provide the host with photosynthetic products but also synthesize specific sunscreen compounds (so-called mycosporine-like amino acids or MAAs)
Not all symbiotic algae are able to synthesize MAAs but provide physical shelter to the ciliates nuclei by accumulating in one cell end. Moreover, many individuals of the ciliate Paramecium bursaria form dense green spots, the so-called ‚collective shield‘. The optimal UV-sunscreen in Paramecium bursaria depends on the amount of symbiotic algae present in the ciliates’ cytoplasm
Ciliates without symbionts
Some ciliates without symbionts may accumulate the sunscreens through MAA-rich algal food
Ciliate plankton in an alpine lake
In alpine lakes the incident solar radiation is high and even the UV-B wavelengths can reach the lake bottom. See how the summer ciliate plankton in such a lake protects itself from high UV-irradiation levels.
UV-photoprotection in Paramecium bursaria
Changes in relative abundance (% of T0) of symbiotic P. bursaria (A), of the cell line with reduced symbiotic algae (B), and of the aposymbiotic (without symbionts) cell line (C) 5 h after exposure to simulated UVR+PAR (photosynthetically active radiation); red bars (left) indicate the relative abundance in the control (i.e., darkness) and orange bars (right) in the UVR treatment; results are reported as the means ± standard deviations for three independent experiments; asterisk indicates a significant difference between control and treatment (p<0.05).