Effects And Mechanisms Of Signal Communication On The Formation And Extracellular Electron Transfer Of Electroactive Biofilm

Bioelectrochemical systems(BESs)have the advantages of wastewater treatment and energy conversion,showing wide application prospects in environmental pollution treatment and energy recovery.Electroactive biofilm is an important functional component of BESs,and the efficiency of extracellular electron transfer(EET)between its interface with the electrode plays a decisive role in the performance of BESs.Therefore,the investigation of the mechanisms of electroactive biofilm formation and EET process is important for optimizing the performance of BESs.Electroactive biofilm formation is regulated by multiple signal communication pathways,including N-acylhomoserine lactone(AHL)-mediated quorum sensing and electrical communication mediated by the release of intracellular potassium and spatial propagation.However,most of the studies on signal communication have been based on the characterization of biofilm physicochemical properties and the regulation of microbial community structure,and in-depth analysis at the molecular mechanism level is still needed.Moreover,studies on the interaction among multiple signal communication pathways are still in the infancy.Herein,the effects and mechanisms of electrical communication and chemical communication on electroactive biofilm formation and EET process were investigated using electrochemistry,confocal laser scanning microscopy visualization and bioinformatics analysis.The main contents and conclusions are as follows:1.Effects of electrical communication disruption on the formation and community structure of electroactive biofilms.Mixed-cultured double-chambered microbial fuel cells(MFCs)were constructed,and a kind of potassium channel blocker(Tetraethylammonium,abbreviated as TEA)was added to the anodic chambers to inhibit the electrical communication.Results showed that electrical communication disruption decelerated the formation of anodic biofilms,but selectively enriched the exoelectrogen Geobacter(relative abundance up to 78.1% on Day90).Although electrical communication disruption reduced the EET efficiency of anodic biofilms during the domestication phase,the final EET efficiency was slightly higher than that of the control due to the selective enrichment of Geobacter by TEA.PICRUSt analysis indicated that there might be other forms of signal communication processes that ultimately contributed to the formation of anodic biofilms in MFC-TEA.2.Compensatory mechanism of chemical communication for electroactive biofilm formation under the disruption of electrical communication.Compensatory mechanism of chemical communication for electroactive biofilm formation was investigated by adding different concentrations of N-(3-oxododecanoyl)-Lhomoserine lactone(HSL for short)under the disruption of electrical communication.The addition of 50 μM HSL could restore anodic biofilm formation rate and EET efficiency to the level of the control.Moreover,the addition of both TEA and exogenous HSL contributed to the selective enrichment of Geobacter,resulting in the relative abundance of Geobacter in anodic biofilm up to 85.5%.Furthermore,the addition of TEA led to a possible predominant role of intracellular bis-(3’-5’)-cyclic dimeric guanosine monophosphate(c-di-GMP)-mediated signaling in anodic biofilms,while the co-addition of TEA and 50 μM HSL led to a possible predominant role of AHL-mediated quorum sensing.Therefore,these two modes of chemical communication could regulate the formation of anodic biofilms in response to changes in the external environment,and c-di-GMP signaling could be more conducive to the adaptation of anodic biofilms to unfavorable external environmental conditions.3.Effects and mechanism of electrical communication disruption on the formation and extracellular electron transfer of G.sulfurreducens biofilm.Pure G.sulfurreducens-based in situ single-chambered MFCs were constructed to investigated the effects of electrical communication disruption on the formation and extracellular electron transfer of G.sulfurreducens biofilm.Electrical communication disruption inhibited the formation and EET efficiency of G.sulfurreducens biofilm,mainly attributed to the decrease of cell viability and extracellular protein/polysaccharide ratio in extracellular polymeric substance(EPS).Transcriptomic results showed that electrical communication disruption resulted in the upregulation of the expression levels of genes associated with c-di-GMP and AHL synthesis.Metabolomic results showed that electrical communication disruption resulted in significant upregulation of N-butyryl-L-homoserine lactone and deoxyguanosine metabolites.Therefore,electrical communication disruption led to enhanced chemical communication,ultimately reinforcing biofilm formation and EET process.4.Signal communication mechanism underlying the effects of tetracycline on the formation and extracellular electron transfer of G.sulfurreducens biofilm.The effects and signal communication mechanisms of tetracycline on the formation and EET efficiency of pure G.sulfurreducens biofilm were investigated by adding different concentrations of tetracycline during biofilm formation.0.05 mg/L of tetracycline promoted biofilm formation,while 1 mg/L tetracycline induced negative effects.Transcriptomic results showed that 0.05 mg/L of tetracycline promoted biofilm formation and EET efficiency mainly by up-regulating the expression of c-di-GMP synthesis genes and thereby promoting intracellular c-di-GMP accumulation.Conversely,1 mg/L tetracycline adversely affected the accumulation of two chemical signal molecules,i.e.,intracellular c-di-GMP and extracellular AHLs,which consequently inhibited biofilm formation and EET efficiency.