| An electrochemically active bacterium(designated as P2-A-5)was isolated from the anodic biofilm of microbial fuel cells(MFCs)that was inoculated with sludge from TEDA Sewage Treatment Plant(Tianjin).Combined with its morphological characteristics,physiological and biochemical properties,16S rDNA sequence analysis,it was identified as Kocuria rhizophila.It is the first time that the strain belonging to K.rhizophila shows electrochemical activity and is applied in MFCs.The single chamber MFCs inoculated with this strain reached a maximum power density of 74.9 mW/m2 with the substrate of 1.0 g/L glucose.To gain insight to the extracellular electron transfer pathway of P2-A-5,the anode-coated MFCs was constructed,the anode solution was analyzed by cyclic voltammetric and GC-MS.And the extracellular electron transfer mechanism was confirmed to be biofilm mechanism.The power performance of strain P2-A-5 was further improved by modifying cells with chemical reagents,optimizing the type and concentration of the substrates.The results showed that strain K.rhizophila P2-A-5 treated with 0.5 mg/L lysozyme for 45 min achieved the highest power density of 314.8 mW/m2 using 2.0 g/L trehalose as substrate,which was 320.3%higher than the original level.The reasons for the increased power density of strain P2-A-5 in MFCs were analyzed by observing the ultramicroscope structure of bacteria,determining the internal resistance and total cell number on the anode of MFCs,determining the cell membrane properties,detecting the composition of fatty acids,measuring the content of key electronic carrier CoQ10 under the chemical treatment.It was found that the improvement of power density was contributed to the significant enhancement on cell adhesion efficiency on electrode,cell permeability and cell membrane fluidity induced by the modification on fatty acid composition,CoQ10 content(the key electron carrier).Different proportions of phenol and glucose mixed solution was further used as substrate of MFCs inoculated with strain P2-A-5.The results showed that,the phenol degradation rate was more than 74%within the concentration of 1000 mg/L.The MFCs achieved the highest voltage of 139 mV with 300 mg/L phenol and 700 mg/L glucose as substrate.The voltage of MFCs continually decreased with the increase of the phenol proportion.When 1000 mg/L phenol was used as the single substrate,the voltage was only 65 mV.These results showed that strain K.rhizophila P2-A-5 could effectively degrade phenol and produce electricity.In addition,the intracellular and extracellular electron transfer pathway of strain Tolumonas osonensis P2-A-1 was preliminary investigated.The results showed that,the extracellular electron transfer mechanism of strain P2-A-1 was confirmed to be dominantly biofilm mechanism and probably produced the electron transfer mediator to assist the electron transfer process.The intracellular electron transfer inhibitors experiments revealed that 9.0 mmol/L rotenone(inhibitor of NADH to CoQ electronic transfer)could inhibit the current generation of MFCs,which indicated that NADH and CoQ was used as the electron carrier of electron transfer approach,NADH and CoQ played an important role in the electron transfer process of strain P2-A-1.7.0 mmol/L NaN3(cytochrome oxidase inhibitor)did not affect the electricity production performance of MFCs,which indicated that cytochrome oxidase was not necessary for the intracellular electron transfer approach of strain P2-A-1.0.5 mmol/L 2,4-dinitrophenol(uncoupling agent),0.5 mmol/L dicyclohexylcarbodiimide(ATPase inhibitor)could also inhibit the current generation of MFCs,which indicated that fermentative metabolism played a certain role in MFCs.The research achievement is of important guidance for enriching the diversity of electricigens,discovering more microbes with high electrochemical activity,improving the electricity production performance and exploring the electron transfer pathway. |
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