Comprehensive Insights into the Role of Hydrogen Bonds in the Anaerobic Fermentation of Insoluble Exopolysaccharides in Waste Activated Sludge: Taking Chondroitin Sulfate as an Example

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Abstract
The hydrogen bond confers the structural recalcitrance of insoluble exopolysaccharides, but its role in the anaerobic fermentation of waste activated sludge (WAS) is seldom reported. As a typical high-molecular-weight exopolysaccharide with poor solubility, chondroitin sulfate (CS) was used to elucidate the role of hydrogen bonds in WAS fermentation. The chondroitin sulfate-degrading consortium (CSDC) was enriched for 180 days, but the methane production was limited (∼18%). The methane production was significantly improved by 88.2%, and extracellular enzyme activity increased by 11.8% after the fast acidic pretreatment of CS. The disruption of the hydrogen bond was confirmed by combining 41.6% reduction of particle size, 46.7% decrease of surface height, blue shifts in the O-H vibrational spectra, and 38.1% decline of interfacial free energy. The molecular dynamics simulation further showed that the hydrogen bond number after the fast acidic pretreatment was reduced from 51.4 ± 2.7 to 44.9 ± 2.1. Co-occurrence network analysis identified Thermovirga as a keystone taxon to facilitate microbial cooperation. The metagenomics and metaproteomics analyses revealed that Proteiniphilum and Mariniphaga served as key producers of extracellular CS-degrading enzymes, primarily CS lyase (EC 4.2.2.5). Above all, these findings demonstrate that the hydrogen bond represents a non-negligible structural constraint on the degradability of insoluble exopolysaccharides.
Funding Information
  • Natural Science Foundation of Fujian Province (2023J01281)
  • Science Fund for Distinguished Young Scholars of Fujian Province (2023J06021)
  • National Natural Science Foundation of China (22576034, 52170127, 52370130)

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