Laboratory of Bioremediation, Department of Environmental Pollution and Process Control, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi-830011, Xinjiang, P.R. China.
Department of Environmental Sciences, Jahangirnagar University, Dhaka, 1342, Bangladesh.
Sci Rep. 2017 Aug 22;7(1):9074. doi: 10.1038/s41598-017-09066-8.
Upon exposure to sunlight extracellular polymeric substances (EPS) were partially transformed into transparent exopolymer particles (TEP) and unstable flocs of different sizes without the addition of any precursors. Parallel factor (PARAFAC) modelling of the sample fluorescence spectra identified humic-like and protein-like or tyrosine-like components in both untreated and irradiated EPS samples. After 58 hours of solar irradiation, humic-like substances were entirely decomposed, while the regenerated protein-like substance from EPS was the key component in the irradiated samples. Degradation and reformation of EPS occurred which was confirmed by the results of size exclusion chromatography, dissolved organic carbon, total protein and total polysaccharide analyses. Irradiated EPS was composed of -COOH or C = O (amide I band) and -NH and -CN (amide II band), while Fourier transform infrared spectroscopy (FTIR) of TEP revealed more acidic -COOH and -C-O groups, indicating typical acidic protein-like TEP. The regenerated protein-like substances could form complexes with free metals originating from degraded EPS in irradiated samples, which could be responsible for the formation of TEP/floc in the aqueous media. These results suggest that TEP/floc formation from EPS could occur by a complexation mechanism between dissolved organic matter and metals, thereby causing ionic charge neutralisation upon sunlight exposure.
在阳光照射下，细胞外聚合物（EPS）部分转化为透明的外聚物颗粒（TEP）和不同大小的不稳定絮体，而无需添加任何前体物质。对样品荧光光谱的平行因子（PARAFAC）建模，在未经辐照和辐照 EPS 样品中均鉴定出类腐殖质和类蛋白质或酪氨酸样成分。在 58 小时的太阳照射后，类腐殖质物质完全分解，而 EPS 中再生的类蛋白质物质是辐照样品中的关键成分。通过尺寸排阻色谱、溶解有机碳、总蛋白和总多糖分析的结果证实 EPS 发生了降解和再形成。辐照 EPS 由 -COOH 或 C ═ O（酰胺 I 带）和 -NH 和 -CN（酰胺 II 带）组成，而 TEP 的傅里叶变换红外光谱（FTIR）显示出更多的酸性 -COOH 和 -C-O 基团，表明典型的酸性蛋白质样 TEP。再生的类蛋白质物质可以与源自辐照样品中降解 EPS 的游离金属形成复合物，这可能是在水介质中形成 TEP/絮体的原因。这些结果表明，TEP/絮体可以通过溶解有机物和金属之间的络合机制从 EPS 中形成，从而导致阳光照射下离子电荷中和。
