Saccharomyces cerevisiae as anodic biocatalyst for power generation in biofuel cell: influence of redox condition and substrate load

Bio (microbial) fuel cell (microbial fuel cell) with Saccharomyces cerevisiae as anodic biocatalyst was evaluated in terms of power generation and substrate degradation at three redox conditions (5.0, 6.0 and 7.0). Fuel cell was operated in single chamber (open-air cathode) configuration without mediators using non-catalyzed graphite as electrodes. The performance was further studied with increasing loading rate (OLRI, 0.91 kg COD/m³-day; OLRII, 1.43 kg COD/m³). Higher current density was observed at pH 6.0 [160.36 mA/m² (OLRI); 282.83 mA/m² (OLRII)] than pH 5.0 (137.24 mA/m²) and pH 7.0 (129.25 mA/m²). Bio-electrochemical behavior of fuel cell was evaluated using cyclic voltammetry which showed the presence of redox mediators (NADH/NAD⁺; FADH/FAD⁺). Higher electron discharge was observed at pH 6.0, suggesting higher proton shuttling through the involvement of different redox mediators. The application of yeast based fuel cell can be extended to treat high strength wastewaters with simultaneous power generation.     

Morphological alterations of Pseudomonas aeruginosa and Escherichia coli by nocardicin A

Abstract Pseudomonas aeruginosa and Escherichia coli were exposed to nocardicin A, and were subsequently observed with transmission and scanning electron microscopes. Although the nocardicin A-induced morphological alterations such as bulges and spheroplast formations were observed both in P. aeruginosa and E. coli , their positions on the cell surface were different in the two species.     

Display of lipase on the cell surface of Escherichia coli using OprF as an anchor and its application to enantioselective resolution in organic solvent

We have developed a new cell surface display system using a major outer membrane protein of Pseudomonas aeruginosa OprF as an anchoring motif. Pseudomonas fluorescens SIK W1 lipase gene was fused to the truncated oprF gene by C-terminal deletion fusion strategy. The truncated OprF-lipase fusion protein was successfully displayed on the surface of Escherichia coli. Localization of the truncated OprF-lipase fusion protein was confirmed by western blot analysis, immunofluorescence microscopy, and whole-cell lipase activity. To examine the enzymatic characteristics of the cell surface displayed lipase, the whole-cell enzyme activity and stability were determined under various conditions. Cell surface displayed lipase showed the highest activity at 37 degrees C and pH 8.0. It retained over 80% of initial activity after incubation for a week in both aqueous solution and organic solvent. When the E. coli cells displaying lipases were used for enantioselective resolution of racemic 1-phenylethanol in hexane, (R)-phenyl ethyl acetate was successfully obtained with the enantiomeric excess of greater than 96% in 36 h of reaction. These results suggest that E. coli cells displaying lipases using OprF as an anchoring motif can be employed for various biotechnological applications both in aqueous and nonaqueous phases.     

Effects of inoculation strategy and cultivation approach on the performance of microbial fuel cell using marine sediment as bio-matrix

Aims: To investigate the effects of inoculation strategy and cultivation approach on the performance of microbial fuel cell (MFC). Methods and Results: A dual‐chamber sediment fuel cell was set up fed with glucose under batch condition. At day 30, the supernatant consortium was partly transferred and used as inoculum for the evaluation of cultivation approach. Power output gradually increased to 9·9 mW m^?2 over 180 days, corresponding to coulombic efficiency (CE) of 29·6%. Separated biofilms attached anode enabled power output and CE dramatically up to 100·9 mW m^?2 and over 50%, respectively, whereas the residual sediment catalysed MFC gave a poor performance. MFC catalysed by in situ supernatant consortium demonstrated more than twice higher power than MFC catalysed by the supernatant consortium after Fe(OH)₃ cultivation. However, the re‐generation of biofilms from the latter largely enhanced the cell performance. Conclusions: MFC exhibited a more efficient inducement of electroactive consortium than Fe(OH)₃ cultivation. MFC performance varied depending on different inoculation strategies. Significance and Impact of the Study: This is the first time to study cultivation approach affecting electricity generation. In addition, anodic limitations of mass and electron transfer were discussed through MFC catalysed by sediment‐based bio‐matrix.     

The antimicrobial mechanism of electrochemically activated water against Pseudomonas aeruginosa and Escherichia coli as determined by SDS-PAGE analysis

Aims:  To expose bacteria to anolyte and subsequently investigate the effect of anolyte on the protein profiles of treated bacteria.
Methods and Results:  Proteins were extracted from bacteria treated with different concentrations of anolyte and analysed using SDS-PAGE. Fewer and more faint protein bands were observed for concentrated halide anolyte treated bacteria when compared to untreated bacteria while extra protein bands were observed for bacteria exposed to dilute concentrations.
Conclusions:  The undiluted and the 10⁻¹ dilution of halide derived anolyte was effective in killing the test bacteria. Anolyte caused bacterial death by complete destruction of proteins or by causing oxidative stress which resulted in protein fragmentation.
Significance and Impact of the Study:  The results of this study provide information on the antimicrobial mechanism of anolyte on other bacteria for which the information is currently unavailable.     

Submersible microbial fuel cell sensor for monitoring microbial activity and BOD in groundwater: Focusing on impact of anodic biofilm on sensor applicability

A sensor, based on a submersible microbial fuel cell (SUMFC), was developed for in situ monitoring of microbial activity and biochemical oxygen demand (BOD) in groundwater. Presence or absence of a biofilm on the anode was a decisive factor for the applicability of the sensor. Fresh anode was required for application of the sensor for microbial activity measurement, while biofilm‐colonized anode was needed for utilizing the sensor for BOD content measurement. The current density of SUMFC sensor equipped with a biofilm‐colonized anode showed linear relationship with BOD content, to up to 250 mg/L (～233 ± 1 mA/m²), with a response time of <0.67 h. This sensor could, however, not measure microbial activity, as indicated by the indifferent current produced at varying active microorganisms concentration, which was expressed as microbial adenosine‐triphosphate (ATP) concentration. On the contrary, the current density (0.6 ± 0.1 to 12.4 ± 0.1 mA/m²) of the SUMFC sensor equipped with a fresh anode showed linear relationship, with active microorganism concentrations from 0 to 6.52 nmol‐ATP/L, while no correlation between the current and BOD was observed. It was found that temperature, pH, conductivity, and inorganic solid content were significantly affecting the sensitivity of the sensor. Lastly, the sensor was tested with real contaminated groundwater, where the microbial activity and BOD content could be detected in <3.1 h. The microbial activity and BOD concentration measured by SUMFC sensor fitted well with the one measured by the standard methods, with deviations ranging from 15% to 22% and 6% to 16%, respectively. The SUMFC sensor provides a new way for in situ and quantitative monitoring contaminants content and biological activity during bioremediation process in variety of anoxic aquifers. Biotechnol. Bioeng. 2011;108: 2339–2347. © 2011 Wiley Periodicals, Inc.     

Simultaneous analysis of physiological and electrical output changes in an operating microbial fuel cell with Shewanella oneidensis

Changes in metabolism and cellular physiology of facultative anaerobes during oxygen exposure can be substantial, but little is known about how these changes connect with electrical current output from an operating microbial fuel cell (MFC). A high‐throughput voltage based screening assay (VBSA) was used to correlate current output from a MFC containing Shewanella oneidensis MR‐1 to carbon source (glucose or lactate) utilization, culture conditions, and biofilm coverage over 250 h. Lactate induced an immediate current response from S. oneidensis MR‐1, with both air‐exposed and anaerobic anodes throughout the duration of the experiments. Glucose was initially utilized for current output by MR‐1 when cultured and maintained in the presence of air. However, after repeated additions of glucose, the current output from the MFC decreased substantially while viable planktonic cell counts and biofilm coverage remained constant suggesting that extracellular electron transfer pathways were being inhibited. Shewanella maintained under an anaerobic atmosphere did not utilize glucose consistent with literature precedents. Operation of the VBSA permitted data collection from nine simultaneous S. oneidensis MR‐1 MFC experiments in which each experiment was able to demonstrate organic carbon source utilization and oxygen dependent biofilm formation on a carbon electrode. These data provide the first direct evidence of complex cellular responses to electron donor and oxygen tension by Shewanella in an operating MFC at select time points. Biotechnol. Bioeng. 2009;103: 524–531. Published 2009 Wiley Periodicals, Inc.     

Integration of a microbial fuel cell with activated sludge process for energy-saving wastewater treatment: taking a sequencing batch reactor as an example

In the research and application of microbial fuel cell (MFC), how to incorporate MFCs into current wastewater infrastructure is an importance issue. Here, we report a novel strategy of integrating an MFC into a sequencing batch reactor (SBR) to test the energy production and the chemical oxygen demand (COD) removal. The membrane-less biocathode MFC is integrated with the SBR to recover energy from the aeration in the form of electricity and thus reduce the SBR operation costs. In a lab-scale integrated SBR-MFC system, the maximum power production of the MFC was 2.34 W/m(3) for one typical cycle and the current density reached up to 14 A/m(3) . As a result, the MFC contributed to the 18.7% COD consumption of the integrated system and also recovered energy from the aeration tank with a volume fraction of only 12% of the SBR. Our strategy provides a feasible and effective energy-saving and -recovering solution to upgrade the existing activated sludge processes.     

Immunoprotective oral whole cell vaccine for enterotoxigenic Escherichia coli diarrhea prepared by in situ destruction of chromosomal and plasmid DNA with colicin E2

Abstract Vaccine regimens which mimic actual infection with bacterial enteropathogens should offer the best opportunity for successful long-term immunoprotection against diarrheal disease caused by enterotoxigenic Escherichia coli (ETEC) or Vibrio cholerae . Based on this principle, we designed and tested an oral whole cell anti-ETEC vaccine consisting of intact cells of ETEC strain H-10407 (ST⁺LT⁺; O78: H11: CFA/I) which were rendered incapable of replication by treatment with a potent DNA endonuclease, colicin E2. Young healthy volunteers were administered two oral doses of either placebo or approx. 3 × 10¹⁰ vaccine cells. In a double-blind study, 9 of 10 vaccinees responded with an increase in CFA/I-specific intestinal IgA antibody, determined as percent of total IgA. Challenge with virulent strain H-10407 (5 × 10⁹ living cells) produced diarrhea in 8 of 9 (89%) of the placebo-treated volunteers and in 2 of 10 (20%) of the vaccinees. Thus, the colicin E2-killed whole cell vaccine afforded both a significant intestinal immune response and significant protection against challenge with the virulent organism. The data presented here suggest that for this vaccine preparation an intestinal anti-CFA/I IgA response is a good indicator of a protective immune response, which most likely involves antibody responses to a number of antigens in addition to CFA/I. We conclude that the colicin E2 method for preparing an oral anti-ETEC vaccine merits further study and that this method may also be applicable to other enteropathogens.