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The aim of this study was to investigate the development of microbial community within the cathodic biofilm of single-chamber air-cathode microbial fuel cell (MFC). To analyze microbial community structures within cathodic biofilm, cathodic biofilm samples were stratified into three layers, i.e., the cathode-side layer (0-40 μm), the middle layer (40-80 μm), and the anolyte-side layer (80-120 μm). After four starting cycles (0-188 h), the maximum power densities of the MFC fed with 1 g/L acetate decreased from 1056 ± 110 to 410 ± 50 mW/m 2 within 15 cycles (~30 d) of operation. The relative abundance of Pseudomonas gradually increased from 18.9% in the 1st cycle to 50.2% in the 4th cycle. After 15 cycles, the relative abundance of Pseudomonas became 53.8%, 16.4%, and 8.90% in the middle, anolyte-side, and cathode-side layers, respectively. The aerobic bacteria within the cathodic biofilm increased from 24% in the anodyte-side layer to 43% in the cathode-side layer. The relative abundance of Methanobrevibacter was 42.1% and 37.2% after 3 and 15 cycles, respectively. The bacterial community structures were similar among cycles 2, 3, and 4, but significantly different in the 15th cycle. The results from this study should be useful to understand the mechanism of the cathodic biofilm formation and to develop strategies to enhance performance of the MFC., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The aim of this study was to investigate the development of cathodic biofilm and its effect on methane production in a single-chamber microbial electrolysis cell (MEC). The MEC with 1 g/L acetate was successfully operated within 31 cycles (∼2400 h). The maximum methane production rate and average current capture efficiency in the MEC reached 93 L/m 3 ·d and 82%, respectively. Distinct stratification of Methanobacteriaceae within cathodic biofilm was observed after 9 cycles of operation. The relative abundance of Methanobacteriaceae in the microbial community increased from 45.3% (0-15 μm), 57.6% (15-30 μm), 66.9% (30-45 μm) to 77.2% (45-60 μm) within the cathodic biofilm. The methane production rates were positively correlated with the mcrA gene copy numbers in the cathodic biofilm. Our results should be useful to understand the mechanism of methane and hydrogen production in the MEC., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The aim of this study was to investigate the microbial stratification structure within cathodic biofilm of the microbial fuel cell (MFC) using the freezing microtome method. Experiments were conducted in a single-chamber air-cathode MFC with 0.8g/L maltodextrin as substrate for ∼30d operation. The maximum power density was 945±10mW/m 2 in the MFC. Maltodextrin resulted in the relative abundance of Candidatus Saccharibacteria of 37.0% in the anodic biofilm. Different bacterial communities were identified in different layers within the cathodic biofilm. The relative abundance of Enterococcus was 3.7%, 10.5%, and 1.6% in the top (100-150μm), middle (50-100μm), and bottom (0-50μm) layers, respectively. Higher bacterial viability was observed within the top and bottom layers of the cathodic biofilm. Understanding the stratification of bacterial community in cathodic biofilm should be important to control the cathodic biofilm in the MFC., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The aim of this study is to investigate the effect of sulfate-reducing bacteria on performance of a mixed culture microbial electrosynthesis system (MES). The two-chamber MESs were operated under different cathode potentials (−0.5, −0.6, −0.7, and −0.8 V) with or without addition of 6 mM sulfate. At −0.7 V, acetate production and electrons harvesting in the MES with the sulfate addition were 31.81 mM and 5152 C, respectively, which improved by 2.7 and 2.4 times compared to that without sulfate. With sulfate, the biomass, proportion of live cells, and electrochemical activity of cathode biofilm were enhanced at all the potentials. At −0.7 V, the relative abundance of Acetobacterium and Desulfovibrionaceae was 14.2% and 36.7% with sulfate, respectively, compared to 17.4% and 7.3% without sulfate. At −0.7 and −0.8 V, the sulfate-reducing bacteria can promote the electron transfer of cathode biofilm and enhance the acetate production. [ABSTRACT FROM AUTHOR]

This study investigated how carbon dots (CDs) and N-doped CDs modification of acetogenic bacteria enhanced the extracellular electron transfer (EET) and the formation of electroactive biofilm, which subsequently improved acetate production from CO 2 in microbial electrosynthesis (MES). Characteristic fluorescence emission peaks of CDs and N-doped CDs were detected inside and outside of bacterial cells, respectively, suggesting that the CDs were successfully internalized by the cells. The (N-doped) CDs modified acetogens increased current output by 89–95%, and acetate production rate by 57–71%. The highest acetate production rate and electron recovery efficiency reached 2.1 mM d−1 and 91.3%, respectively. Acetoanaerobium and Sporomusa , which are considered to have different EET strategies, dominated the biocathodes modified with CDs and N-doped CDs, respectively. The CDs modification increased biofilm thickness by 86% and reached 41.0 ± 1.3 μm, which could be related to the increased secretion of flavins that enhanced the signal transduction interspecies. With the N-doped CDs modified, the biofilm was occupied with active pyrrolic N/graphitic N (52%), and the expression of functional genes encoding cytochrome (cydB , cybH, CcdA) were enhanced significantly. This study offers insights into the EET mechanisms by acetogens and a viable approach to increase acetate production from CO 2. [Display omitted] • CDs and N-doped CDs modified acetogens enhanced the MESs performance. • Electron recovery efficiency for acetate production was >89% with CDs modified. • Acetoanaerobium and Sporomusa dominated the biofilm with (N-doped) CDs modified. • CDs modification promoted the secretion of redox active substances such as flavins. • N-doped CDs enhanced the biofilm EET by introducing active pyrrolic N. [ABSTRACT FROM AUTHOR]

[Display omitted] • NH 4 +-N and TN removals were decreased with the external resistance decreasing. • NO 2 –-N accumulation of 4.4 ± 0.8 mg/L was observed within cycle 13 under 10 Ω. • The highest abundance of Glutamicibacter was 60.9% at layer 5 of cathodic biofilm. • AOB was closer to the cathode under lower external resistance. The aim of this study was to investigate the effect of external resistance on the physiological stratification of cathodic biofilms in the air–cathode single-chamber microbial fuel cell (MFC) during the nitrogen removal. The mature cathode biofilm of MFC after 13 cycles operation (∼900 h) was sliced into five layers, each with a thickness of 20 to 30 μm, to determine the physiological stratification of the cathode biofilm. With the external resistance decreasing from 1000 to 10 Ω, the NH 4 +-N and total nitrogen removals was decreased from 90.3 ± 9.0 % and 89.4 ± 9.0 % to 75.3 ± 8.0 % and 67.5 ± 7.0 %, respectively. Ammonia-oxidizing bacteria was closer to the cathode under lower external resistance, while denitrifying bacteria dominated the community far from the cathode under different external resistances. Results from this study should be useful for understanding the nitrogen removal in the cathodic biofilm of MFC. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate pH effect on stratification of bacterial community in cathodic biofilm of the microbial fuel cell (MFC) under alkaline conditions. A single-chamber MFC with air-cathode was operated with 0.8 g/L maltodextrin and bicarbonate buffer solutions under pH values of 8.5, 9.5, and 10.5, respectively. The cathodic biofilms were characterized by linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), confocal laser scanning microscopy (CLSM), freezing microtome and high-throughput sequencing analysis on bacterial communities, respectively. Results showed that the maximum power densities in the MFC increased with the pH values and reached 1221 ± 96 mW/m2 at pH = 10.5 during ∼30 d of operation. With different pH values, the composition and relative abundance of bacterial community significantly changed in the bottom (0–50 μm), middle (50–100 μm), and top (100–150 μm) layers of the cathodic biofilm. With pH = 10.5, aerobic bacteria accounted for 12%, 13%, and 34% of the bacterial community in the top, middle, and bottom layers, respectively. The amount of anaerobic bacteria in the top and middle layers (i.e., 52%, and 50% of the bacterial community, respectively) was higher than that in the bottom layer (22%). The distribution of aerobic and anaerobic bacteria showed a "valley-peak" structure within the layers. The high CO 3 2− concentration facilitates the hydroxyl transfer and the neutralization in the anode of the MFC under high alkali conditions. The results from this study should be useful to develop new catalyst and cathode in the MFC. Image 1 • The maximum power densities in the MFC increased with the pH values. • High alkalinity inhibited the bicarbonate working as the proton carrier. • pH had great effect on stratification of bacterial community in cathodic biofilm. • A "valley-peak" structure within the biofilm layers in the cathode was observed. [ABSTRACT FROM AUTHOR]