EcoLab, Université de Toulouse, CNRS, INPT, UPS, Toulouse, France.
LBAE, Université de Toulouse, UPS, Auch, France.
Environ Sci Pollut Res Int. 2019 Dec;26(34):35107-35120. doi: 10.1007/s11356-019-06560-6. Epub 2019 Nov 2.
In freshwater ecosystem, phototrophic biofilms play a crucial role through adsorption and sequestration of organic and inorganic pollutants. However, extracellular polymeric substance (EPS) secretion by phototrophic biofilms exposed to metals is poorly documented. This work evaluated the physiological responses of phototrophic biofilms by exposing three microorganisms (cyanobacterium Phormidium autumnale, diatom Nitzschia palea and green alga Uronema confervicolum) to 20 and 200 μg L of Cu or 60 and 600 μg L of Zn, both individually and in combination. Analysis of metal effects on algal biomass and photosynthetic efficiency showed that metals were toxic at higher concentrations for these two parameters together and that all the strains were more sensitive to Cu than to Zn. U. confervicolum was the most impacted in terms of growth, while P. autumnale was the most impacted in terms of photosynthetic efficiency. In consequence to metal exposure at higher concentrations (Cu200, Zn600 and Cu200Zn600), a higher EPS production was measured in diatom and cyanobacterium biofilms, essentially caused by an overproduction of protein-like polymers. On the other hand, the amount of secreted polysaccharides decreased during metal exposure of the diatom and green alga biofilms. Size exclusion chromatography revealed specific EPS molecular fingerprints in P. autumnale and N. palea biofilms that have secreted different protein-like polymers during their development in the presence of Zn600. These proteins were not detected in the presence of Cu200 despite an increase of proteins in the EPS extracts compared to the control. These results highlight interesting divergent responses between the three mono-species biofilms and suggest that increasing protein production in EPS biofilms may be a fingerprint of natural biofilm against metal pollutants in freshwater rivers.
在淡水生态系统中，通过对有机和无机污染物的吸附和隔离，光养生物膜发挥了关键作用。然而，光养生物膜在暴露于金属时分泌的胞外聚合物（EPS）却鲜有记录。本研究通过将三种微生物（蓝藻 Phormidium autumnale、硅藻 Nitzschia palea 和绿藻 Uronema confervicolum）分别暴露于 20 和 200μg/L 的 Cu 或 60 和 600μg/L 的 Zn ，以及二者的混合物中，评估了光养生物膜的生理反应。对金属对藻类生物量和光合作用效率的影响分析表明，对于这两个参数，金属在较高浓度下具有毒性，并且所有菌株对 Cu 的敏感性都高于 Zn。在生长方面，U. confervicolum 受影响最大，而在光合效率方面，P. autumnale 受影响最大。因此，在较高浓度（Cu200、Zn600 和 Cu200Zn600）的金属暴露下，在硅藻和蓝藻生物膜中测量到更高的 EPS 产量，这主要是由蛋白质样聚合物的过度产生引起的。另一方面，在硅藻和绿藻生物膜暴露于金属时，分泌的多糖量减少。尺寸排阻色谱法揭示了 P. autumnale 和 N. palea 生物膜中 EPS 的特定分子指纹，这些生物膜在存在 Zn600 的情况下分泌不同的蛋白质样聚合物。尽管 EPS 提取物中的蛋白质与对照相比有所增加，但在存在 Cu200 时并未检测到这些蛋白质。这些结果突出了三种单种生物膜之间有趣的差异反应，并表明 EPS 生物膜中蛋白质产量的增加可能是淡水河流中天然生物膜抵御金属污染物的特征指纹。
