| Electroactive biofilms（EABs）oriented from mixed inoculum is attractive due to its unique nature of direct extracellular electron transfer and potential use in biotoxicity detection.Bioelectrochemical systems（BESs）is one of the most interesting biofilm systems treating wastewater with simultaneous electricity generation with less sludge production.In these systems,the quick formation of EABs from mixed inoculum was vital to the anode performance.Here we for the first time demonstrated a chemical that can be used for EABs regulation（both inhibition and promotion）.Tobramycin,an antibiotic previously demonstrated to inhibit the activity of EABs,is confirmed as an agonist at subminimal inhibitory concentration（sub-MIC）during EABs formation.At tobramycin concentrations of 0.05（1/80 MIC）and 0.1 mg/L（1/40 MIC）,the time needed to reach3 A/m2 was 9%shorter,and the limiting current densities based on cyclic voltammetry increased by 17%and 7%than the control.The enhanced EAB activity was primarily attributed to the 50%increase of biomass density from 289±21 to 434±12?g protein/cm2 and the increased biofilm thickness from 28±1 to 37±0.5?m.Geobacter in microbial community was selectively increased from 76%to 82%,and its population was estimated to increase by 1.63 times.Higher concentration of 0.3 mg/L inhibited the EAB activity.In addition,the regulation mechanism of 1/80 tobramycin was studied by G.sulfurreducens PCA.The control and the 1/80 tobramycin group showed the“S”type growth.After 72h,the biomass of 0.05 mg/L tobramycin sample increased by 29.5%compared to the control.0.3 mg/L of tobramycin completely inhibited the proliferation of G.sulfurreducens PCA.During the cultivation,the OD600 of this sample stabilized at 0.07±0.003.Sequencing analysis revealed that 1/80 inhibition concentration tobramycin resulted in a significant up-regulation of cytochrome omcB,omcT,omcS,omcC,omcE,ppcA,omcN and IV type pilus protein synthesis genes pilA-C,pilA-N,pilR,pilS and pilC.That illustrated that sub-MIC tobramycin have promoted electron transfer of G.sulfurreducens PCA.No matter in the mixed or pure cultures,sub-MIC of tobramycin were all shown to regulate the growth of EABs.Ceftazidime was not found to promote the formation of EAB biofilm.Nevertheless,the mature biofilm which was inoculated with 0.5 g/L ceftazidime have resistances to the secondary addition of the same concentration of antibiotics.The limited current densities based on CVs have no obvious attenuation,but under the same conditions,the control decreased by 32%.The electron transfer between the anode and biofilm plays an important role in the current output of BESs,the key factor affecting the electron transfer between EABs and anode is the activity of EABs.These findings provided a novel and effective way to regulate EAB formation,which is vital for the investigation of intercellular electron transfer especially in mixed microbial community in the future. |
