Quorum sensing-Fe metabolism interplay affects biofouling on reverse osmosis membrane: Evidences from microbial shift and structure alteration

Iron fouling induced by residual Fe(III) was frequently reported in reverse osmosis operation. However, previous studies mainly focused on inorganic precipitation or Fe-organics coupling, yet ignoring its potential effects on microbes. In this study, by using ultrafiltration effluent (~2.3 mg/L Fe(III)) as the feed, a long-term fouling experiment was conducted to investigate how excessive Fe influenced biofouling. Results showed, under continuous stresses of Fe-deposits (eventually >40 μg/cm 2 ), fouling development clearly exhibited a three-stage process, where Fe-metabolism, extracellular polymeric substance synthesis and quorum sensing (QS) were intricately intertwined. Compared to Early (3 h–2 d) and Developed (4 d–10 d) Stage, ecological interaction network in Mature Stage (12 d–30 d) was shifted and highly modularized, with iron-depositing genera (such as Leptothrix ) in emerging Fe-metabolic modules as the core nodes . Foulant structure was also more porous. Moreover, by detecting signal molecules, the upregulation of QS was unraveled. Functional gene co-occurrence analysis further revealed the profound involvement of QS in enhancing polysaccharides (PS) secretion and ferric-reduction, which were verified by the constantly rising PS proportion and Fe(II)/Fe(III) ratio on surface. Therefore, more attentions should be paid to residual Fe-issues, as it not only affected inorganic fouling, but also significantly altered biofouling behaviors.