Potassium channel blocker selectively enriched Geobacter from mixed-cultured electroactive biofilm: Insights from microbial community, functional prediction and gene expressions

Quorum quenching inhibits the formation and electroactivity of electrogenic biofilm by weakening intracellular c-di-GMP and extracellular AHL-mediated signal communication

Electrogenic biofilm formation has been shown to be induced by intracellular c-di-GMP signaling and extracellular quorum sensing, but their interactions have been rarely explored. This study explored the effects of quorum quenching (induced by adding acylase) on electrogenic biofilm development and its underlying mechanisms. Quorum quenching impaired the electricity generation and electroactivity of electrogenic biofilms as indicated by dye decolorization rate. It significantly decreased the proportion of typical exoelectrogen Geobacter from 62.0% to 36.5% after 90 days of operation, and enriched some other functional genera (e.g., Dysgonomonas and Sphaerochaeta) to ensure normal physiological function. Moreover, metagenomic analysis revealed that the addition of acylase weakened the potential of chemical communication, as indicated by the decrease in the abundance of genes encoding the production of AHL and c-di-GMP, and the increase in the abundance of aiiA and pvdQ genes (encoding quorum quenching) and cdgC gene (responsible for c-di-GMP breakdown). Functional contribution analysis indicated that Geobacter was a major contributor to hdtS gene (encoding AHL synthesis). These findings demonstrated that quorum quenching adversely impaired not only quorum sensing but also intracellular c-di-GMP signaling, ultimately inhibiting the development of biofilm. This work lays the foundation for regulating electrogenic biofilm development and improving the performance of microbial electrochemical system using signal communication strategy.

Effects of potassium-mediated electrical communication inhibition on nitrogen removal in microbial fuel cells

Potassium ion signaling mediates microbial communication in electroactive biofilms within microbial fuel cells (MFCs), but its role in nitrogen removal remains unclear. This study investigated the impact of inhibiting potassium signaling on nitrogen removal in MFCs using tetraethylammonium chloride (TEA) as an inhibitor. Results demonstrated that 5 mM and 10 mM TEA reduced the maximum power generation of MFCs from 77.95 mW/cm2 to 57.18 mW/cm2 and 48.23 mW/cm2, respectively. Correspondingly, total nitrogen (TN) removal efficiency was decreased from 46.57 ± 1.01% to 35.93 ± 0.63% and 38.97 ± 0.74%, respectively. This decline was attributed to inhibited potassium ion signaling, which compromised the electrochemical performance of the MFC and hindered the nitrogen removal process. The relative abundance of exoelectrogen Geobactor decreased from 15.37% to 5.17% and 8.05%, while the relative abundance of cathodic nitrifying bacteria Nitrosomonas decreased from 17.87% to 4.92% and 3.63% under 5 mM and 10 mM TEA. These findings underscore the crucial role of potassium ion signaling in enhancing the bioelectrochemical nitrogen removal process in MFCs.

Enhanced thermophilic high-solids anaerobic digestion of organic fraction of municipal solid waste with spatial separation from conductive materials in a single reactor volume

Despite benefits such as lower water and working volume requirements, thermophilic high solids anaerobic digestion (THSAD) often fails due to the rapid build-up of volatile fatty acids (VFAs) and the associated drop in pH. Use of conductive materials (CM) can promote THSAD through stimulation of direct interspecies electron transfer (DIET), while the need for their constant dosing due to poor separation from effluent impairs economic feasibility. This study used an approach of spatially separating magnetite and granular activated carbon (GAC) from the organic fraction of municipal solid waste (OFMSW) in a single reactor for THSAD. GAC and magnetite addition could both mitigate the severe inhibition of methanogenesis after VFAs build-up to ∼28-30 g/L, while negligible methane production was observed in the control group. The highest methane yield (286 mL CH4/g volatile solids (VS)) was achieved in magnetite-added reactors, while the highest maximum CH4 production rates (26.38 mL CH4/g VS/d) and lowest lag-phase (2.83 days) were obtained in GAC-added reactors. The enrichment of GAC and magnetite biofilms with various syntrophic and potentially electroactive microbial groups (Ruminiclostridium 1, Clostridia MBA03, Defluviitoga, Lentimicrobiaceae) in different relative abundances indicates the existence of specific preferences of these groups for the nature of CM. According to predicted basic metabolic functions, CM can enhance cellular processes and signals, lipid transport and metabolism, and methane metabolism, resulting in improved methane production. Rearrangement of metabolic pathways, formation of pili-like structures, enrichment of biofilms with electroactive groups and a significant improvement in THSAD performance was attributed to the enhancement of the DIET pathway. Promising results obtained in this work due to the spatial separation of the bulk OFMSW and CM can be useful for modeling larger-scale THSAD systems with better recovery of CM and cost-effectiveness.

Electroactive properties of EABs in response to long-term exposure to polystyrene microplastics/nanoplastics and the underlying adaptive mechanisms

Given widespread presence of polystyrene (PS) microplastics/nanoplastics (MPs/NPs), the electroactive responses and adaptation mechanisms of electroactive biofilms (EABs) exposed long-term to PS-containing aquatic environments remain unclear. Therefore, this study investigated the impacts of PS MPs/NPs on electroactivity of EABs. Results found that EABs exhibited delayed formation upon initially exposure but displayed an increased maximum current density (Imax) after subsequent exposure for up to 55 days. Notably, EABs exposure to NH2PS NPs (EAB-NH2PSNPs) demonstrated a 50% higher Imax than the control, along with a 17.84% increase in viability and a 58.10% increase in biomass. The cytochrome c (c-Cyts) content in EAB-NH2PSNPs rose by 178.35%, benefiting the extracellular electron transfer (EET) of EABs. Moreover, bacterial community assembly indicated the relative abundance of electroactive bacteria increased to 87.56% in EAB-NH2PSNPs. The adaptability mechanisms of EABs under prolonged exposure to PS MPs/NPs predominantly operate by adjusting viability, EET, and bacterial community assembly, which were further confirmed a positive correlation with Imax through structural equation model. These findings provide deeper insights into long-term effects and mechanisms of MPs/NPs on the electroactive properties of EABs and even functional microorganisms in aquatic ecosystems.

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.