UV‐acclimation responses in natural populations of cyanobacteria (Calothrix sp.)

Abstract

Phenotypic acclimation to changing conditions is typically thought to be beneficial to organisms in the environment. UV radiation is an important parameter affecting photosynthetic organisms in natural environments. We measured the response of photosynthetic carbon fixation in populations of cyanobacteria inhabiting a hot spring following acclimation to different UV treatments. These two very closely related populations of cyanobacteria, differing in their content of the extracellular UV-screening pigment scytonemin, were acclimated in situ under natural solar irradiance modified by filters that excluded both UVA/B, only UVB or transmitted both UVA/B. Cells from each preacclimation treatment were subsequently assayed for photosynthetic performance under all UV conditions (incubation treatment) giving a two-factor experimental design for each population. No acclimation filter treatment effects were observed even after two months under different acclimation treatments. This suggests that UV photoacclimation does not occur in either of these populations, regardless of the presence of scytonemin. By contrast, cells showed significant UV-inhibition during 1 h incubations under full sun. The population with high levels of scytonemin usually had lower rates of photosynthetic carbon fixation than the scytonemin-lacking population. However, the degree of UV inhibition, especially UVA inhibition, was higher for the cells without scytonemin pigment. These results suggest that closely related natural cyanobacterial populations respond differently to natural irradiance conditions and may be adopting different strategies of UV tolerance.

Epilithic Cyanobacterial Communities of a Marine Tropical Beach Rock (Heron Island, Great Barrier Reef): Diversity and Diazotrophy

“…Organisms inhabiting such beach rocks must be resilient to extreme stresses, such drastic salinity changes, desiccation, and highly fluctuating light and UV regimens between the periods of full submersion (high tide). Hence, these organisms must possess numerous tolerance and adaptive mechanisms (14). In the tropics, rocky shores are dominated by primary producers such as cyanobacteria.…”

Parasite-Host Specificity: Experimental Studies on the Basis of Parasite Adaptation

“…Specialization with a large plastic component has, for example, been demonstrated in plant-herbivore interactions where insect herbivores adapt physiologically to the deterrent allelochemicals produced by their hosts (e.g., Jermy 1990; Akhtar and Isman 2004). Plasticity, sometimes called phenotypic acclimation, is also frequently assumed in studies of microorganisms (Bennett and Lenski 1997;Dillon et al 2003;Rainey 2004). In many cases, it may be difficult to determine when specialization is due to genetic differences or differential patterns of expression among strains with the same genetic background.…”

Microscopic examination of photoautotrophic and phosphatase-producing organisms in phosphorus-limited Everglades periphyton mats

“…2a). The top mat layers were pale yellow to white in color, probably the result of photobleaching at the water surface and/or the presence of high concentrations of the pigment scytonemin (Dillon et al 2003). Deeper mat layers were not exposed to high intensities of solar radiation, and as a result, they appear green from the dominance of Notes photosynthetic cyanobacteria and green algae.…”