High Power Density from a Miniature Microbial Fuel Cell Using \u3ci\u3eShewanella oneidensis\u3c/i\u3e DSP10

A miniature microbial fuel cell (mini-MFC) is described that demonstrates high output power per device crosssection (2.0 cm2) and volume (1.2 cm3). Shewanella oneidensis DSP10 in growth medium with lactate and buffered ferricyanide solutions were used as the anolyte and catholyte, respectively. Maximum power densities of 24 and 10 mW/m2 were measured using the true surface areas of reticulated vitreous carbon (RVC) and graphite felt (GF) electrodes without the addition of exogenous mediators in the anolyte. Current densities at maximum power were measured as 44 and 20 mA/m2 for RVC and GF, while short circuit current densities reached 32 mA/m2 for GF anodes and 100 mA/m2 for RVC. When the power density for GF was calculated using the cross sectional area of the device or the volume of the anode chamber, we found values (3 W/m2, 500 W/m3) similar to the maxima reported in the literature. The addition of electron mediators resulted in current and power increases of 30-100%. These power densities were surprisingly high considering a pure S. oneidensis culture was used. We found that the short diffusion lengths and high surface-area-to-chamber volume ratio utilized in the mini-MFC enhanced power density when compared to output from similar macroscopic MFCs

High Power Density from a Miniature Microbial Fuel Cell Using \u3ci\u3eShewanella oneidensis\u3c/i\u3e DSP10

A miniature microbial fuel cell (mini-MFC) is described that demonstrates high output power per device crosssection (2.0 cm2) and volume (1.2 cm3). Shewanella oneidensis DSP10 in growth medium with lactate and buffered ferricyanide solutions were used as the anolyte and catholyte, respectively. Maximum power densities of 24 and 10 mW/m2 were measured using the true surface areas of reticulated vitreous carbon (RVC) and graphite felt (GF) electrodes without the addition of exogenous mediators in the anolyte. Current densities at maximum power were measured as 44 and 20 mA/m2 for RVC and GF, while short circuit current densities reached 32 mA/m2 for GF anodes and 100 mA/m2 for RVC. When the power density for GF was calculated using the cross sectional area of the device or the volume of the anode chamber, we found values (3 W/m2, 500 W/m3) similar to the maxima reported in the literature. The addition of electron mediators resulted in current and power increases of 30-100%. These power densities were surprisingly high considering a pure S. oneidensis culture was used. We found that the short diffusion lengths and high surface-area-to-chamber volume ratio utilized in the mini-MFC enhanced power density when compared to output from similar macroscopic MFCs

Laboratory growth of denitrifying water column microbial consortia from deep-sea shipwrecks in the northern Gulf of Mexico [version 2; referees: 2 approved]

Background: Shipwrecks serve as a rich source for novel microbial populations that have largely remained undiscovered. Low temperatures, lack of sunlight, and the availability of substrates derived from the shipwreck’s hull and cargo may provide an environment in which microbes can develop unique metabolic adaptations.   Methods: To test our hypothesis that shipwrecks could influence the microbial population involved in denitrification when a consortium is grown in the laboratory, we collected samples proximate to two steel shipwrecks in the northern Gulf of Mexico. Then under laboratory conditions, we grew two independent denitrifying microbial consortia. Each consortium was grown by using the BART assay system and analyzed based on growth kinetics, ion chromatography and 16S amplicon sequencing. Results: Both denitrifying consortia were different from each other based on varied growth profiles, rates of nitrate utilization and 16S amplicon sequencing. Conclusions: Our observations conclude that the laboratory grown water column microbial consortia from deep-sea shipwrecks in the Gulf of Mexico are able to undergo aggressive denitrification

Laboratory growth of denitrifying water column microbial consortia from deep-sea shipwrecks in the northern Gulf of Mexico [version 3; referees: 2 approved]

Background: Shipwrecks serve as a rich source for novel microbial populations that have largely remained undiscovered. Low temperatures, lack of sunlight, and the availability of substrates derived from the shipwreck’s hull and cargo may provide an environment in which microbes can develop unique metabolic adaptations.   Methods: To test our hypothesis that shipwrecks could influence the microbial population involved in denitrification when a consortium is grown in the laboratory, we collected samples proximate to two steel shipwrecks in the northern Gulf of Mexico. Then under laboratory conditions, we grew two independent denitrifying microbial consortia. Each consortium was grown by using the BART assay system and analyzed based on growth kinetics, ion chromatography and 16S amplicon sequencing. Results: Both denitrifying consortia were different from each other based on varied growth profiles, rates of nitrate utilization and 16S amplicon sequencing. Conclusions: Our observations conclude that the laboratory grown water column microbial consortia from deep-sea shipwrecks in the Gulf of Mexico are able to undergo aggressive denitrification

Hydration dynamics at fluorinated protein surfaces

Water-protein interactions dictate many processes crucial to protein function including folding, dynamics, interactions with other biomolecules, and enzymatic catalysis. Here we examine the effect of surface fluorination on water-protein interactions. Modification of designed coiled-coil proteins by incorporation of 5,5,5-trifluoroleucine or (4S)-2-amino-4-methylhexanoic acid enables systematic examination of the effects of side-chain volume and fluorination on solvation dynamics. Using ultrafast fluorescence spectroscopy, we find that fluorinated side chains exert electrostatic drag on neighboring water molecules, slowing water motion at the protein surface

Evaluation of Two Models for Human Topoisomerase I Interaction with dsDNA and Camptothecin Derivatives

Human topoisomerase I (Top1) relaxes supercoiled DNA during cell division. Camptothecin stabilizes Top1/dsDNA covalent complexes which ultimately results in cell death, and this makes Top1 an anti-cancer target. There are two current models for how camptothecin and derivatives bind to Top1/dsDNA covalent complexes (Staker, et al., 2002, Proc Natl Acad Sci USA 99: 15387–15392; and Laco, et al., 2004, Bioorg Med Chem 12: 5225–5235). The interaction energies between bound camptothecin, and derivatives, and Top1/dsDNA in the two models were calculated. The published structure-activity-relationships for camptothecin and derivatives correlated with the interaction energies for camptothecin and derivatives in the Laco et al. model, however, this was not the case for several camptothecin derivatives in the Stacker et al. model. By defining the binding orientation of camptothecin and derivatives in the Top1/dsDNA active-site these results allow for the rational design of potentially more efficacious camptothecin derivatives

A biofilm enhanced miniature microbial fuel cell using \u3ci\u3eShewanella oneidensis\u3c/i\u3e DSP10 and oxygen reduction cathodes

Aminiature-microbial fuel cell (mini-MFC, chamber volume: 1.2 mL)was used to monitor biofilm development from a pure culture of Shewanella oneidensis DSP10 on graphite felt (GF) under minimal nutrient conditions. ESEM evidence of biofilm formation on GF is supported by substantial power density (per device cross-section) from the mini-MFC when using an acellular minimal media anolyte (1500mW/m2). These experiments demonstrate that power density per volume for a biofilm flow reactor MFC should be calculated using the anode chamber volume alone (250 W/m3), rather than with the full anolyte volume. Two oxygen reduction cathodes (uncoated GF or a Pt/vulcanized carbon coating on GF) were also compared to a cathode using uncoated GF and a 50mM ferricyanide catholyte solution. The Pt/C-GF (2–4% Pt by mass) electrodes with liquid cultures of DSP10 produced one order of magnitude larger power density (150 W/m3) than bare graphite felt (12 W/m3) in this design. These advances are some of the required modifications to enable the mini-MFC to be used in real-time, long-term environmental power generating situations

Simultaneous Analysis of Physiological and Electrical Output Changes in an Operating Microbial Fuel Cell With \u3ci\u3eShewanella oneidensis\u3c/i\u3e

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

The influence of acidity on microbial fuel cells containing \u3ci\u3eShewanella oneidensis\u3c/i\u3e

Microbial fuel cells (MFCs) traditionally operate at pH values between 6 and 8. However, the effect of pH on the growth and electron transfer abilities of Shewanella oneidensis MR-1 (wild-type) and DSP10 (spontaneous mutant), bacteria commonly used in MFCs, to electrodes has not been examined. Miniature MFCs using bare graphite felt electrodes and nanoporous polycarbonate membranes with MR-1 or DSP10 cultures generated \u3e8W/m3 and ∼400μA between pH 6–7. The DSP10 strain significantly outperformed MR-1 at neutral pH but underperformed at pH 5. Higher concentrations of DSP10 were sustained at pH 7 relative to that of MR-1, whereas at pH 5 this trend was reversed indicating that cell count was not solely responsible for the observed differences in current. S. oneidensis MR-1 was determined to be more suitable than DSP10 for MFCs with elevated acidity levels. The concentration of riboflavin in the bacterial cultures was reduced significantly at pH 5 for DSP10, as determined by high performance liquid chromatography (HPLC) of the filter sterilized growth media. In addition, these results suggest that mediator biosynthesis and not solely bacterial concentration plays a significant role in current output from S. oneidensis containing MFCs

Laboratory Growth of Denitrifying Water Column Microbia Consortia From Deep-Sea Shipwrecks in the Northern Gulf of Mexico

Background: Shipwrecks serve as a rich source for novel microbial populations that have largely remained undiscovered. Low temperatures, lack of sunlight, and the availability of substrates derived from the shipwreck’s hull and cargo may provide an environment in which microbes can develop unique metabolic adaptations. Methods: To test our hypothesis that shipwrecks could influence the microbial population involved in denitrification when a consortium is grown in the laboratory, we collected samples proximate to two steel shipwrecks in the northern Gulf of Mexico. Then under laboratory conditions, we grew two independent denitrifying microbial consortia. Each consortium was grown by using the BART assay system and analyzed based on growth kinetics, ion chromatography and 16S amplicon sequencing. Results: Both denitrifying consortia were different from each other based on varied growth profiles, rates of nitrate utilization and 16S amplicon sequencing. Conclusions: Our observations conclude that the laboratory grown water column microbial consortia from deep-sea shipwrecks in the Gulf of Mexico are able to undergo aggressive denitrification