Werner Nadine, Orfanoudaki Maria, Hartmann Anja, Ganzera Markus, Sommaruga Ruben
Department of Ecology University of Innsbruck Innsbruck Austria.
Institute of Pharmacy Pharmacognosy University of Innsbruck Innsbruck Austria.
Freshw Biol. 2021 Jan;66(1):169-176. doi: 10.1111/fwb.13627. Epub 2020 Oct 15.
Cyanobacteria are one of the oldest organisms on Earth and they originated at a time when damaging ultraviolet (UV) C radiation still reached the surface. Their long evolution led to several adaptations to avoid deleterious effects caused by exposure to solar UV radiation. Synthesis of sunscreen substances, such as mycosporine-like amino acids (MAAs), allows them to photosynthesise with reduced risk of cell damage. The interplay of solar UV radiation and MAAs is well documented for cyanobacteria in the plankton realm, but little is known for those in the benthic realm, particularly of clear alpine lakes.Here, we assessed the temporal dynamics of MAAs in the benthic algal community of one clear alpine lake dominated by cyanobacteria during the ice-free season and along a depth gradient using state-of-the-art analytical methods (high-performance liquid chromatography, nuclear magnetic resonance, liquid chromatography-mass spectrometry). We differentiated between the epilithic cyanobacterial community and the overlying loosely attached filamentous cyanobacteria, as we expected they will have an important shielding/shading effect on the former. We hypothesised that in contrast to the case of phytoplankton, benthic cyanobacteria will show less pronounced temporal changes in MAAs concentration in response to changes in solar UV exposure.Three UV-absorbing substances were present in both types of communities, whereby all were unknown. The chemical structure of the dominant unknown substance (maximum absorption at 334 nm) resulted in the identification of a novel MAA that we named aplysiapalythine-D for its similarity to the previously described aplysiapalythine-C.Chlorophyll--specific MAA concentrations for epilithic and filamentous cyanobacteria showed a significant decrease with depth, although only traces were found in the former community. The temporal dynamics in MAA concentrations of filamentous cyanobacteria showed no significant variations during the ice-free season.Our result on the low temporal MAA dynamics agrees with the reduced growth rates of benthic cyanobacteria reported for cold ecosystems. The permanent presence of this community, which is adapted to the high UV levels characteristic of clear alpine lakes, probably represents the most important primary producers of these ecosystems.
蓝细菌是地球上最古老的生物之一，它们起源于有害的紫外线C辐射仍能到达地球表面的时期。它们漫长的进化过程导致了几种适应机制，以避免暴露于太阳紫外线辐射所造成的有害影响。合成防晒物质，如类菌孢素氨基酸（MAAs），使它们能够在细胞受损风险降低的情况下进行光合作用。太阳紫外线辐射与MAAs之间的相互作用在浮游生物领域的蓝细菌中已有充分记录，但对于底栖生物领域的蓝细菌，尤其是清澈的高山湖泊中的蓝细菌，人们了解甚少。在此，我们使用先进的分析方法（高效液相色谱法、核磁共振法、液相色谱 - 质谱联用），评估了一个以蓝细菌为主的清澈高山湖泊在无冰季节沿深度梯度的底栖藻类群落中MAAs的时间动态。我们区分了附着在岩石上的蓝细菌群落和覆盖其上的松散丝状蓝细菌，因为我们预计后者会对前者产生重要的屏蔽/遮蔽作用。我们假设，与浮游植物的情况不同，底栖蓝细菌对太阳紫外线暴露变化的响应中，MAAs浓度的时间变化不太明显。两种群落中都存在三种紫外线吸收物质，但均为未知物质。主要未知物质（最大吸收波长为334nm）的化学结构导致鉴定出一种新型MAA，因其与先前描述的aplysiapalythine - C相似，我们将其命名为aplysiapalythine - D。附着在岩石上的蓝细菌和丝状蓝细菌中叶绿素特异性MAA浓度随深度显著降低，尽管在前一个群落中仅发现微量。丝状蓝细菌中MAA浓度的时间动态在无冰季节没有显著变化。我们关于MAA时间动态较低的结果与寒冷生态系统中报道的底栖蓝细菌生长速率降低一致。这个适应了清澈高山湖泊高紫外线水平的群落的永久存在，可能是这些生态系统中最重要的初级生产者。
