活性污泥微生物胞外多聚物生物合成途径与菌胶团形成的调控机制

Biosynthesis pathway of extracellular polymeric substance and regulatory mechanism underlying floc formation of activated sludge bacteria

摘要:

活性污泥法是借助活性污泥微生物菌胶团形成来实现泥水重力分离和部分污泥回用，辅以曝气供氧，在曝气池中高密度的微生物细胞可将溶解性有机污染物迅速降解、转化后为己所用，外排的剩余污泥带走大量有机质和氮磷，水质得以净化。活性污泥微生物所合成的胶质状胞外多聚物(extracellular polymeric substances，EPS)是污泥菌胶团形成必不可少的“黏合剂”，吸水性极高，这也造成剩余污泥难以处置和利用。我们初步总结了活性污泥微生物宏基因组研究概况，利用分子遗传学和基因组学手段，对活性污泥优势种动胶菌(Zoogloea)和其他菌胶团形成菌的EPS生物合成途径和菌胶团形成与调控机制加以研究，鉴定出一个约40 kb的胞外多糖生物合成大型基因簇和一个由7个基因组成的小型基因簇，该基因簇中除胞外多糖合成相关基因外，还编码组氨酸激酶PrsK和反应调节蛋白PrsR双组分系统，可激活RpoN σ因子共同调控一类称之为PEP-CTERM的新型胞外蛋白质的表达，参与菌胶团的形成。PEP-CTERM富含天冬酰胺(缩写为Asn或者N)残基，可能与胞外多糖通过N-连锁的糖基化形成复合物，包裹微生物细胞群体来介导菌胶团的形成。类似的PEP-CTERM基因和胞外多糖合成基因簇在许多重要的活性污泥细菌如聚磷菌和全程氨氧化菌中存在，说明这些细菌也是菌胶团形成菌，可通过污泥沉淀和回用在活性污泥中得以富集。这些研究结果可供活性污泥膨胀控制、污泥减量和剩余污泥资源和能源回收利用参考。

Abstract:

The activated sludge (AS) process has been widely applied for municipal sewage and industrial wastewater treatment for over a century. The microbial floc formation plays a central role in gravitational sludge-effluent separation and sludge recycling. However, very little was known about the mechanism underlying the floc formation of activated sludge bacteria. By summarizing the literature about AS microbiome, molecular biology of AS floc formation and comparative genomics analyses to reveal the molecular mechanism underlying bacterial floc formation. The extracellular polysaccharide biosynthesis gene cluster is widespread among floc-forming bacteria and is required for bacterial floc formation, which was experimentally confirmed in Zoogloea, Thauera, Mitsuaria and Aquincola strains. Furthermore, the prsK-prsR-prsT gene cluster and PEP-CTERM genes are also widely encoded in those floc-forming bacteria. and other genes. It is demonstrated that bacterial floc formation mediated by both exopolysaccharides and PEP-CTERM proteins might be well-conserved among AS bacteria and other floc-formers. These results could provide important implications for the control of sludge bulking, reduction of sludge, and resource and energy recovery from excess sludge.