Felz Simon, Kleikamp Hugo, Zlopasa Jure, van Loosdrecht Mark C M, Lin Yuemei
Department of Biotechnology, Delft University of Technology, Van der Maasweg 9, 2629 HZ, Delft, the Netherlands.
Biofilm. 2019 Dec 3;2:100011. doi: 10.1016/j.bioflm.2019.100011. eCollection 2020 Dec.
Structural extracellular polymeric substances (structural EPS) can form stable hydrogels and are considered to be responsible for the stability of biofilms and aerobic granular sludge. Structural EPS were extracted from aerobic granular sludge and characterized for their gel-forming capacity with different alkaline earth and transition metal ions. The structural EPS hydrogels were compared to alginate hydrogels. Alginate is a well characterized polymer which is able to form stiff hydrogels with multivalent ions. The stiffness of the obtained hydrogels was measured with dynamic mechanical analysis and quantified by the Young's modulus. Furthermore the stability of structural EPS hydrogels towards disintegration in the presence of ethylenediaminetetraacetic acid (EDTA) was evaluated at pH 4.5-10.5 and compared to that of alginate, polygalacturonic acid and κ-carrageenan. The stiffness of alginate hydrogels was multiple times higher than that of structural EPS. Alkaline earth metals resulted in stiffer alginate hydrogels than transition metals. For structural EPS this trend was opposite to alginate. Independent of the pH, polysaccharide hydrogels were quickly disintegrated when being exposed to EDTA. Structural EPS hydrogels demonstrated greater stability towards EDTA and were still intact after one month at pH 4.5-8.5. It is suggested that the gelling mechanism of structural EPS is not only related to metal ion complexation of the polymers, but to a combination of interactions of multiple functional groups present in structural EPS. This study helps to further understand and characterize structural EPS from aerobic granular sludge, and therewith understand its stability and that of biofilms in general.
结构性胞外聚合物（结构性胞外多糖）可形成稳定的水凝胶，被认为对生物膜和好氧颗粒污泥的稳定性起作用。从好氧颗粒污泥中提取结构性胞外多糖，并对其与不同碱土金属和过渡金属离子形成凝胶的能力进行表征。将结构性胞外多糖水凝胶与藻酸盐水凝胶进行比较。藻酸盐是一种特性明确的聚合物，能够与多价离子形成坚硬的水凝胶。通过动态力学分析测量所得水凝胶的硬度，并用杨氏模量进行量化。此外，在pH值为4.5 - 10.5的条件下，评估了结构性胞外多糖水凝胶在乙二胺四乙酸（EDTA）存在下抗崩解的稳定性，并与藻酸盐、聚半乳糖醛酸和κ-卡拉胶的稳定性进行比较。藻酸盐水凝胶的硬度比结构性胞外多糖水凝胶高好几倍。碱土金属使藻酸盐水凝胶比过渡金属形成的更硬。对于结构性胞外多糖，这种趋势与藻酸盐相反。无论pH值如何，多糖水凝胶在暴露于EDTA时都会迅速崩解。结构性胞外多糖水凝胶对EDTA表现出更高的稳定性，在pH值为4.5 - 8.5的条件下放置一个月后仍保持完整。研究表明，结构性胞外多糖的凝胶化机制不仅与聚合物的金属离子络合有关，还与结构性胞外多糖中存在的多个官能团的相互作用组合有关。这项研究有助于进一步了解和表征好氧颗粒污泥中的结构性胞外多糖，从而总体上了解其稳定性以及生物膜的稳定性。
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