Enhancement of stress resistance of electroactive biofilms against hypersaline shock via exogenous electron mediator addition

[Display omitted] •AQDS addition enhanced the hypersaline tolerance of electroactive biofilms (EB).•Improved protein and Cyts-C in EPS improved electrochemical properties of EB.•AQDS addition builds complex microbial network to resist hypersaline shock.•EB developed under AQDS addition showed superior recovery post-hypersaline stress.•AQDS boosts the function abundance of pressure tolerance and biofilm formation. Unexpected hypersaline shock from saline wastewater poses a common challenge in the biological treatment processes of WWPTs. Bioelectrochemical systems (BESs) possess an inherent advantage for treating hypersaline wastewater. The elevated salinity enhances the wastewater’s conductivity, which in turn significantly accelerates the electron and proton transfer within the system. However, excessive increases in salinity can impede electron transport capacity, potentially resulting in cell plasmolysis and system failure in severe instances. Here, we investigated the impact of electron mediator (EM) addition on the resilience of electroactive biofilms (EB) to hypersaline environments in BESs. The EB developed under anthraquinone-2,6-disulphonic disodium salt (AQDS) addition obtained preferable electrochemical properties (e.g., current output, redox peak current, conductivity, electron transfer capacity) under hypersaline shock and showed superior recovery post-hypersaline stress. Partial least squares path modeling (PLS-PM) analysis indicated that the enhanced secretion of extracellular polymeric substances (EPS) and the elevated ratio of proteins to polysaccharides are likely pivotal in the formation of EB with high electrochemical activity. Meanwhile, AQDS addition constructed more complex microbial network and enriched halotolerant bacteria (e.g., Solibacillus). Higher mean function abundance of replication & repair, stress tolerance, and biofilm formation were achieved by EM addition. The results of this study present a promising approach to augment the pressure tolerance of EBs, thereby broadening the practical applications of BESs.