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Flocculation and Transparent Exopolymer Particles Formation of Microbial Mat Extracellular Polymeric Substances from a Hypersaline Lake
Mashura Shamm
Thesis AdvisorPan Xiangliang(潘响亮) ; Khan M. G. Mostofa ; Daoyong Zhang
Degree Grantor中国科学院大学
Place of Conferral新疆乌鲁木齐
Degree Discipline博士
KeywordExtracellular Polymeric Substances (Eps) Transparent Exopolymeric Particles (Tep) Dissolved Organic Carbon (Doc) Locculation Zeta−potential Particle Size Distribution (Psd)
AbstractThis study investigated the mechanism of flocculation and transparent exopolymer particles (TEP) formation of extracellular polymeric substances (EPS) from mixed algal-bacterial biofilm mat from hypersaline lakes. Various spectrophotometric techniques were employed along with parallel factor (PARAFAC) modelling on the sample excitation-emission matrix (EEM) spectra. EPS with exposure to sunlight was found to form larger TEP and floc particles of variable sizes, confirmed from turbidity test, ζ−potential (−mV) and PSD (d.nm) assay in the first few hours of sunlight exposure. It further suggested that floc/TEP formation from EPS could occur by charge neutralization and bridging mechanism. Correspondingly, EEM-PARAFAC identified humic-like and protein-like or tryptophan-like components in both raw and treated EPS samples. After the fifth day of solar irradiation, humic-like substances were entirely decomposed whilst the regenerated protein-like substances from EPS were the key components remained in irradiated samples. Degradation of EPS, particularly protein molecules of EPS was observed from the result of HPLC−SEC, which was confirmed from degradation of DOC, total protein and total polysaccharide analysis. FTIR of treated EPS and filtered EPS had more –COOH, C−H, and –C–O groups indicating acidic polysaccharide typical of TEP. With increasing pH, EPS flocculated with increasing PSD (d.nm) while a decrease in PSD (d.nm) was observed with decreasing pH. Microscopic images with AB dye assay showed a significant increase in floc/TEP at pH 10 followed by pH 8.Incubation over 24 hours with different concentration of NaCl (0 mM to 60 mM) had noteworthy effect on floc/TEP formation. But AB dye assay image with NaCl treatment showed no significant differences in floc/TEP size by changing the concentration of NaCl. ATR-FTIR spectroscopy analysis confirmed C=O and C–N groups. The carboxylic and phenolic (–COO− /–O − ) containing protein molecules in EPS might be responsible for EPS-metal (Mn+)–protein or EPS- metal (Mn+)-polysaccharide complexation by higher pH and Na+/Cl−leading to TEP/flocformation.The TEP/floc formation mechanism of EPS in response to different divalent cations (Fe2+, Ca2+ and Mg2+) with different concentrations (2 mM, 0.5 mM and 10µM) were observed. In the course of time a significant charge drop was observed with increasing concentration of Fe2+ followed by a larger floc/TEP formation in the first six hours. However, the larger floc/TEP broken down into daughter particles in the next 24 hours (approximately ~1652 d.nm). Microscopic investigation of AB dye confirmed fibrillar amorphous floc/TEP formation after 24 hours of incubation EPS adjusted with FeCl2 , CaCl2 and MgCl2. PSD assay confirmed highest floc/TEP formation in FeCl2 treatment compared to CaCl2 and MgCl2 treated EPS. ζ−potential, PSD and turbidity assay confirmed that particle bridging and particle breakage were dominant. Excitation-emission (EEM) spectroscopy along with parallel factor (PARAFAC) analysis confirmed protein-like, tryptophan-like and humic-like substances of EPS formed complexes through donation of their electrons to Fe2+, Ca2+,Mg2+ and that subsequently formed TEP/floc. It is, therefore, evidence from the above experiments that EPS can transform itself into the floc/TEP in a natural environment by the influence of sunlight, pH, salinity and different types of divalent cations that alter the geochemical interaction in natural waters.
Other Abstract本文采用各种分光光度技术以及平行因子(PARAFAC)建模、样品激发发射矩阵(EEM)光谱,研究了来自超级盐水湖的混合藻类细菌生物膜的絮凝和透明聚合物颗粒(TEP)形成细胞外聚合物质(EPS)的机制。 EPS 暴露于阳光几个小时后,通过测定浊度测试、ζ-电位(-mV)和 PSD(d.nm)可知,EPS 形成更大颗粒的 TEP 和可变尺寸的絮状颗粒。该结果表明,通过电荷中和和桥接机理,EPS 可形成 floc/ TEP。 相应地,经过 EEM-PARAFAC 对原始和经处理的EPS 样品进行鉴定,得出 EPS 的成分为腐殖质、蛋白质、色氨酸。 经过 5 天太阳辐射后,腐殖质物质被完全分解,而来自 EPS 的再生蛋白质物质是 EPS 重要的分解成分。由 HPLC-SEC、DOC、总蛋白质、多糖的检测可知,EPS 发生了降解与重组,特别是 EPS 的蛋白质分子。 经过 FTIR 分析可知,处理的 ESPs 比未处理的 EPS 具有更多的-COOH,C-H 和-C-O 基团,这暗示 TEP 具有酸性多糖的特征。随着 pH 的增加,EPS 絮凝体随着 PSD(d.nm)的增加而增加,而随着 pH值的降低,PSD(d.nm)也随之下降。 用 AB 染色的显微镜图像显示:pH 由 8升高至 10,floc/TEP 显著增加。由不同浓度的 NaCl(0 mM至 60 mM)孵育 floc/TEP 24 小时可知,NaCl 对絮凝物/ TEP 形成几乎没有影响。AB 染色成像和 NaCl 处理显示,NaCl 浓度的变化对 floc/TEP 的尺寸影响不大。 ATR-FTIR 光谱分析证实,EPS 和处理 EPS 中均有 C = O 和 C-N 基团。 EPS 的蛋白质分子含有羧酸和酚(-COO -/ - O- ),是由于在较高 pH 和 Na+/Cl- 条件下 EPS 与金属蛋白络合或 EPS 与多糖络合而致使 TEP /絮凝物形成。探讨了不同阳离子(Fe2+、Ca2+和 Mg2+)和不同离子浓度(2 mM、0.5 mM 和10µM)对 EPS 的 TEP /絮凝物形成机理的影响。 反应 6 h 后,EPS 电位随着 Fe2+浓度增加显著下降,是由于生成了一个大粒径的 floc/TEP。然而,24 h 后,较大的絮凝物/ TEP 裂解成小颗粒物(颗粒粒径约为 0 ~1652 d.nm)。 AB 染色显微观察证实,floc/TEP 是不定性状的纤维状絮凝体。PSD测定结果证实,相比 CaCl2和 MgCl2的处理组,FeCl2处理组有更多 floc/ TEP 形成。EPS+FeCl 2经过孵化 24h,有不定性状的纤维状絮凝体形成。 Ζ-电位、PSD 和浊度测定结果证实,颗粒桥接和颗粒断裂起主导作用。发射矩阵光谱和平行因子分析证实,EPS 中的类蛋白质物质、类色氨酸物质、类腐殖酸物质与 Fe2+、Ca2+、Mg2+络合形成了TEP/floc。综上所述,在自然环境的阳光辐射下,EPS 可以自己转变成为 floc/TEP。在阳光、pH、不同阳离子影响下,最终改变天然水域的地球化学相互作用。
Subject Area生态学
Document Type学位论文
2.Institute of Surface-Earth System Science, Tianjin University
3.Xinjiang Institute of Ecology and Geography
Recommended Citation
GB/T 7714
Mashura Shamm. Flocculation and Transparent Exopolymer Particles Formation of Microbial Mat Extracellular Polymeric Substances from a Hypersaline Lake[D]. 新疆乌鲁木齐. 中国科学院大学,2017.
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