title: Acute Responses of Microorganisms from Membrane Bioreactors in the Presence of NaOCl: Protective Mechanisms of Extracellular Polymeric Substances.
abstract: Extracellular polymeric substances (EPS) are key foulants in membrane bioreactors (MBRs). However, their positive functions of protecting microorganisms from environmental stresses, e.g., during in situ hypochlorite chemical cleaning of membranes, have not been adequately elucidated. In this work, we investigated the response of microorganisms in an MBR to various dosages of NaOCl, with a particular emphasis on the mechanistic roles of EPS. Results showed that functional groups in EPS such as the hydroxyl and amino groups were attacked by NaOCl, causing the oxidation of polysaccharides, denaturation of amino acids, damage to protein secondary structure, and transformation of tryptophan protein-like substances to condensed aromatic ring substances. The presence of EPS alleviated the negative impacts on catalase and superoxide dismutase, which in turn reduced the concentration of reactive oxygen species (ROS) in microbial cells. The direct extracellular reaction and the mitigated intracellular oxidative responses facilitated the maintenance of microbial metabolism, as indicated by the quantity of adenosine triphosphate and the activity of dehydrogenase. The reaction with NaOCl also led to the changes of cell integrity and adhesion properties of EPS, which promoted the release of organic matter into bulk solution. Our results systematically demonstrate the protective roles of EPS and the underlying mechanisms in resisting the environmental stress caused by NaOCl, which provides important implications for in situ chemical cleaning in MBRs.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University , 1239 Siping Road, Shanghai 200092, China.|Shanghai Urban Water Resources Development and Utilization National Engineering Center Co. Ltd. , Shanghai 200082, China.
authors.forename: Xiaomeng
authors.initials: X
authors.lastname: Han
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University , 1239 Siping Road, Shanghai 200092, China.
authors.forename: Zhiwei
authors.identifier: 0000-0001-6729-2237
authors.initials: Z
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University , 1239 Siping Road, Shanghai 200092, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University , 1239 Siping Road, Shanghai 200092, China.
authors.forename: Xingran
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Civil Engineering, The University of Hong Kong , Pokfulam, Hong Kong China.
authors.forename: Chuyang Y
authors.initials: CY
authors.lastname: Tang
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University , 1239 Siping Road, Shanghai 200092, China.
authors.forename: Zhichao
authors.initials: Z
authors.lastname: Wu
mesh_terms: D019149:Bioreactors; D008567:Membranes, Artificial; D011108:Polymers
chemical_list: D008567:Membranes, Artificial; D011108:Polymers