Effects Of N-Acyl-L-Homoserine Lactone Signaling Molecules On The Electricigenic Respiration Of Electroactive Biofilm

Bioelectrochemical systems(BES)are promising technologies that use electroactive biofilm(EAB)as catalysts to drive oxidation and/or reduction reactions at electrodes.Such systems,with characteristics of low fabrication cost,Low energy consumption and environmental benignity,have great applications in environmental.And it perfectly couple microbial metabolism with electrochemical reactions,in which EAB play an important role.Biofilm formation and maturation can be regulated by distinct forms of communication factors.Generally,most of the gram-negative bacteria employ the class of N-acylhomoserine lactones(AHL)as chemical signals.To our knowledge,the impact of AHL on EAB especially the typical electroactive microorganism(Geobacter)has been paid less attention.In this study,we established the mixed-culture and pure-culture BES to investigate the electricigenic respiration in response to the AHL by characterizing the redox activities of EAB,electro-conductivities,biomass,the ratio of live/dead cells and the compactness of the entire biofilm,the electron-accepting capacities/electron-donating capacities and concentration of extracellular polymeric substance(EPS).And explore the inmost mechanisms from protein level.The main results and conclusions are as follows:(1)Three exogenous AHL(C4-HSL,C6-HSL and 30C12-HSL)and one acylase(for endogenous AHL)were taken to test effects on mixed-cultured BES.The results showed that,the start-up period of BES were accelerated by 6 days and 3 days with exogenous and endogenous AHL,respectively.The coulombic efficiency(CE) increased from 28.3 ± 4.1%to 35.5 ± 5.5%(C4-HSL),35.2 ± 5.8%(C6-HSL)and 36.2 ± 5.1%(30C12-HSL)and CE increased by?8%by endogenous AHL.The electricity generation of EAB was improved in presence of exogenous and/or endogenous AHL via increasing the redox activities of EAB,lectro-conductivities,biomass,the ratio of live/dead cells and the compactness of the entire biofilm,the electrochemical activities and concentration of EPS.Besides,endogenous AHL enhance the diversity of EPS components.(2)The results of high-throughput sequencing showed the relative abundance of typical Geboacter sp.increased from an average of 56%to a 71-78%,78 ± 6%(C6-HSL)and 71 ± 6%(30C12-HSL)with addition of exogenous AHL.It is reasonable to propose that all the above conspire to obtain superior mixed-culture EAB.While endogenous AHL have on response for the relative abundance of Geoboacter sp..(3)Based on conclusion(2),we established the pure-culture BES of Geobacter soli GSS01 to explore the electricigenic respiration and the formation of EAB.The most electricity generation was increased by 50%and 20%by exogenous and endogenous AHL,respectively and the set-up period of BES was shorted by 2 and 1 cycle.Same to mixed-culture EAB,the electricity generation of EAB was improved in presence of exogenous and/or endogenous AHL via increasing the redox activities of EAB,lectro-conductivities,biomass,the ratio of live/dead cells and the compactness of the entire biofilm,the electrochemical activities and concentration of EPS.Unlike the mixed-culture EAB,the film formation process of GSS01 was measured.(4)The in situ FTIR-2D and quantitative proteomics analysis were used to characterize the EAB.The results showed exogenous AHL have no response on individual GSS01 to expression the protein and the membrane protein group.COG with the largest number of up-regulated proteins were represented by "energy production and conversion","amino acid transport and metabolism" and "inorganic ion transport and metabolism" with addition acylase.This implied that endogenous AHL have greatest influence on these three functions.The response rate change sequence of outmost groups to the shifting potentials followed the order:amide ?(extended p-strand)? heme modes for control,heme modes ? amide ? with addition C6-HSL,and C-O stretching ? binding of CH2/CH3 ? amide ? amide ?(P-turn)in presence of acylase.It indicated that the distinct influence of endogenous chemical signals and the limited effect of exogenous chemical signals on individual Geobacter soli.