Potassium channel mediates electroactive biofilm formation via recruiting planktonic Geobacter cells

c-di-GMP and AHL signals-triggered chemical communication under electrical signaling disruption restores Geobacter sulfurreducens biofilm formation

Electrogenic biofilms, which have attracted considerable attention in simultaneous wastewater treatment and energy recovery in bioelectrochemical systems, are regulated by chemical communication and potassium channel-mediated electrical signaling. However, how these two communication pathways interact with each other has not been thoroughly investigated. This study first explored the roles of chemical communication, including intracellular bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) and extracellular N-acyl-homoserine lactone (AHL)-mediated quorum sensing, in electrogenic biofilm formation through an integrated analysis of transcriptomics and metabolomics. Electrical signaling disruption inhibited the formation and electroactivity of Geobacter sulfurreducens biofilm, which was mainly ascribed to the reduction in biofilm viability and extracellular protein/polysaccharide ratio. The upregulation of expression levels of genes encoding c-di-GMP and AHL synthesis by transcriptomic analysis, and the increased secretion of N-butanoyl-L-homoserine lactone by metabolomic analysis confirmed the enhancement of chemical communication under electrical signaling disruption, thus indicating a compensatory mechanism among different signaling pathways. Furthermore, protein-protein interaction network showed the convergence of different signaling pathways, with c-di-GMP-related genes acting as central bridges. This study highlights the interaction of different signaling pathways, especially the resilience of c-di-GMP signaling to adverse external stresses, thereby laying the foundation for facilitating electrogenic biofilm formation under adverse conditions in practical applications.

Revealing the roles of chemical communication in restoring the formation and electroactivity of electrogenic biofilm under electrical signaling disruption

Electrogenic biofilms in microbial electrochemical systems have played significant roles in simultaneous wastewater treatment and energy recovery owing to their unique extracellular electron transfer. Their formation has been shown to be regulated by electrical and chemical communication, but the interaction between these signal communication pathways has not been studied. This research investigated the coordination between intracellular c-di-GMP signaling and reinforced quorum sensing with or without exogenous HSL (a common quorum sensing molecule), on the formation of mixed-cultured electrogenic biofilm under electrical signaling disruption by tetraethylammonium (TEA, a broad-range potassium channel blocker). Intracellular c-di-GMP was spontaneously reinforced in response to TEA stress, and metagenomic analysis revealed that the dominant DGC (the genes for producing c-di-GMP) induced the eventual biofilm formation by mediating exopolysaccharide synthesis. Meanwhile, reinforced quorum sensing by exogenous HSL could also benefit the biofilm restoration, however, it alleviated the TEA-induced communication stress, resulting in the weakening of c-di-GMP dominance. Interestingly, suppressing electrical communication with or without HSL addition both induced selective enrichment of Geobacter of 85.5% or 30.1% respectively. Functional contribution analysis revealed the significant roles of Geobacter and Thauera in c-di-GMP signaling, especially Thauera in resistance to TEA stress. This study proposed a potential strategy for electrogenic biofilm regulation from the perspectives of cell-to-cell communication.

Transcriptome sequencing reveals the difference in the expression of biofilm and planktonic cells between two strains of Salmonella Typhimurium

Salmonela enterica serovar Typhimurium (S. Typhimurium) is a food-borne pathogen that can form biofilms to increase its resistance to the external environment. Through the detection of biofilm of several S. Typhimurium strains in this study, strain CDC3 with strong biofilm forming capacity and strain CVCC3384 with weak biofilm forming capacity were identified. The genes expressed in planktonic and biofilm cells of two S. Typhimurium strains were analysed by transcriptome sequencing. Results showed that the genes related to the signal transduction pathway were upregulated and genes related to motility were downregulated in strain CDC3. By comparing biofilms and planktonic cells of the two strains, we found that CDC3 regulates biofilm formation mainly through the two-component system kdpABC, while strain CVCC3384 does so mainly through motility and quorum sensing. This study revealed regulation mechanism of biofilms formation between different biofilm forming capacity strains, and provided a theoretical basis for subsequent research.