Stability improvement and the mechanism of a microbial electrolysis cell biocathode for treating wastewater containing sulfate by quorum sensing

Abstract

The treatment of sulfate-containing wastewater by microbial electrolysis cells (MEC) is a feasible method, but the biocathode suffers from poor microbial stability. The phenomenon of quorum sensing (QS) has offered the opportunity to overcome these weaknesses. Nevertheless, it has not been well evaluated how QS improves microbial stability performance and which enzymes and genes influence microbial activity. In this study, N-butyryl-l-Homoserine lactone (C4-HSL) was added as a typical QS signaling molecule to the biocathode in MEC. Sulfate reduction efficiency, microbial community structure, and related functional genes were analyzed comprehensively. The results showed that the sulfate reduction efficiency and biocathode stability were higher under the regulation of C4-HSL. Results indicated that the number of microorganisms on the electrode surface was more than that of the control group, and the percentage of live cells was 22% higher after the regulation by C4-HSL. In addition, the C4-HSL regulation stimulated the growth of the hydrogen producer (Desulfomicrobium), Homoacetogens (Acetoanaerobium), and part of Anaerobic fermentation bacteria (Macellibacteroides and Lentimicrobium). Metagenomic sequencing elucidated the phenomenon of QS mainly through an exponential increase in autoinducer-producer-related genes and cysteine/methionine metabolism pathways. The regulation by C4-HSL mainly affected genes controlling surface proteins and biofilm formation, which resulted in higher activity and more stability of biofilms. And the relative abundance of functional genes associated with sulfate reduction metabolism was increased, which positively affected the assimilatory sulfate reduction and dissimilatory sulfate reduction pathways. These findings reveal the potential and mechanisms of the QS signaling molecule in enhancing MEC for sulfate-containing wastewater treatment.