Orianna Bretschger | J. Craig Venter Institute (original) (raw)

Papers by Orianna Bretschger

F1000 - Post-publication peer review of the biomedical literature, Feb 11, 2020

Users may view, print, copy, and download text and data-mine the content in such documents, for t... more Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Enzyme and microbial technology, 2011

Chitosan (CHIT) scaffolds doped with multi-walled carbon nanotubes (CNT) were fabricated and eval... more Chitosan (CHIT) scaffolds doped with multi-walled carbon nanotubes (CNT) were fabricated and evaluated for their utility as a microbial fuel cell (MFC) anodic material. High resolution microscopy verified the ability of Shewanella oneidensis MR-1 to directly colonize CHIT-CNT scaffolds. Cross-linking agents 1-ethyl-3-[3-dimethylaminopropyl] carbodimide hydrochloride (EDC), glutaraldehyde and glyoxal were independently studied for their ability to strengthen the CHIT-CNT matrix without disrupting the final pore structure. 2.5 vol% glyoxal was found to be the optimal cross-linker in terms of porosity (BET surface area = 30.2 m 2 g −1 ) and structural stability. Glyoxyl and EDC cross-linked CHIT-CNT scaffolds were then studied for their ability to transfer electrons to underlying glassy carbon. Results showed an open circuit cell voltage of 600 mV and a maximum power density of 4.75 W/m 3 at a current density of 16 A/m 3 was achieved in non stirred batch mode, which compares well with published data using carbon felt electrodes where a power density of 3.5 W/m 3 at a current density of 7 A/m 3 have been reported. Additionally, CHIT-CNT scaffolds were impregnated into carbon felt electrodes and these results suggest that CHIT-CNT scaffolds can be successfully integrated with multiple support materials to create hybrid electrode materials. Further, preliminary tests indicate that the integrated scaffolds offer a robust macroporous electrode material that can be used in flow-through configurations.

RSC Advances, 2012

Mediated electron transfer has been implicated as a primary mechanism of extracellular electron t... more Mediated electron transfer has been implicated as a primary mechanism of extracellular electron transfer to insoluble electron acceptors in anaerobic cultures of the facultative anaerobe Shewanella oneidensis. In this work, planktonic and biofilm cultures of S. oneidensis exposed to carbon-limited environments trigger an electrochemical response thought to be the signature of an electrochemically active metabolite. This metabolite was detected via cyclic voltammetry for S. oneidensis MR-1 biofilms. The observed electrochemical potentials correspond to redox potentials of flavin-containing molecules. Chromatographic techniques were then used to quantify concentrations of riboflavin by the carbon-limited environmental response of planktonic S. oneidensis. Further evidence of flavin redox chemistry was associated with biofilm formation on multi-walled carbon nanotube-modified Toray paper under carbon-starved environments. By encapsulating one such electrode in silica, the encapsulated biofilm exhibits riboflavin redox activity earlier than a non-encapsulated system after media replacement. This work explores the electrochemical nature of riboflavin interaction with an electrode after secretion from S. oneidensis and in comparison to abiotic systems.

Bioelectrochemistry (Amsterdam, Netherlands), Jan 6, 2015

Self-assembled monolayers (SAMs) modified gold anodes are used in single chamber microbial fuel c... more Self-assembled monolayers (SAMs) modified gold anodes are used in single chamber microbial fuel cells for organic removal and electricity generation. Hydrophilic (N(CH3)3(+), OH, COOH) and hydrophobic (CH3) SAMs are examined for their effect on bacterial attachment, current and power output. The different substratum chemistry affects the community composition of the electrochemically active biofilm formed and thus the current and power output. Of the four SAM-modified anodes tested, N(CH3)3(+) results in the shortest start up time (15days), highest current achieved (225μAcm(-2)) and highest MFC power density (40μWcm(-2)), followed by COOH (150μAcm(-2) and 37μWcm(-2)) and OH (83μAcm(-2) and 27μWcm(-2)) SAMs. Hydrophobic SAM decreases electrochemically active bacteria attachment and anode performance in comparison to hydrophilic SAMs (CH3 modified anodes 7μAcm(-2) anodic current and 1.2μWcm(-2) MFC's power density). A consortium of Clostridia and δ-Proteobacteria is found on all t...

Microbial fuel cells (MFCs) traditionally operate at pH values between 6 and 8. However, the effe... more 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 >8 W/m 3 and ∼400 A 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.

PLoS ONE, 2012

Microbial fuel cells (MFCs) are devices that exploit microorganisms as biocatalysts to recover en... more Microbial fuel cells (MFCs) are devices that exploit microorganisms as biocatalysts to recover energy from organic matter in the form of electricity. One of the goals of MFC research is to develop the technology for cost-effective wastewater treatment. However, before practical MFC applications are implemented it is important to gain fundamental knowledge about long-term system performance, reproducibility, and the formation and maintenance of functionally-stable microbial communities. Here we report findings from a MFC operated for over 300 days using only primary clarifier effluent collected from a municipal wastewater treatment plant as the microbial resource and substrate. The system was operated in a repeatbatch mode, where the reactor solution was replaced once every two weeks with new primary effluent that consisted of different microbial and chemical compositions with every batch exchange. The turbidity of the primary clarifier effluent solution notably decreased, and 97% of biological oxygen demand (BOD) was removed after an 8-13 day residence time for each batch cycle. On average, the limiting current density was 1000 mA/m 2 , the maximum power density was 13 mW/m 2 , and coulombic efficiency was 25%. Interestingly, the electrochemical performance and BOD removal rates were very reproducible throughout MFC operation regardless of the sample variability associated with each wastewater exchange. While MFC performance was very reproducible, the phylogenetic analyses of anode-associated electricity-generating biofilms showed that the microbial populations temporally fluctuated and maintained a high biodiversity throughout the year-long experiment. These results suggest that MFC communities are both self-selecting and self-optimizing, thereby able to develop and maintain functional stability regardless of fluctuations in carbon source(s) and regular introduction of microbial competitors. These results contribute significantly toward the practical application of MFC systems for long-term wastewater treatment as well as demonstrating MFC technology as a useful device to enrich for functionally stable microbial populations. Citation: Ishii S, Suzuki S, Norden-Krichmar TM, Nealson KH, Sekiguchi Y, et al. (2012) Functionally Stable and Phylogenetically Diverse Microbial Enrichments from Microbial Fuel Cells during Wastewater Treatment. PLoS ONE 7(2): e30495.

The ISME Journal, 2014

Microbial extracellular electron transfer (EET) to solid surfaces is an important reaction for me... more Microbial extracellular electron transfer (EET) to solid surfaces is an important reaction for metal reduction occurring in various anoxic environments. However, it is challenging to accurately characterize EET-active microbial communities and each member&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s contribution to EET reactions because of changes in composition and concentrations of electron donors and solid-phase acceptors. Here, we used bioelectrochemical systems to systematically evaluate the synergistic effects of carbon source and surface redox potential on EET-active microbial community development, metabolic networks and overall electron transfer rates. The results indicate that faster biocatalytic rates were observed under electropositive electrode surface potential conditions, and under fatty acid-fed conditions. Temporal 16S rRNA-based microbial community analyses showed that Geobacter phylotypes were highly diverse and apparently dependent on surface potentials. The well-known electrogenic microbes affiliated with the Geobacter metallireducens clade were associated with lower surface potentials and less current generation, whereas Geobacter subsurface clades 1 and 2 were associated with higher surface potentials and greater current generation. An association was also observed between specific fermentative phylotypes and Geobacter phylotypes at specific surface potentials. When sugars were present, Tolumonas and Aeromonas phylotypes were preferentially associated with lower surface potentials, whereas Lactococcus phylotypes were found to be closely associated with Geobacter subsurface clades 1 and 2 phylotypes under higher surface potential conditions. Collectively, these results suggest that surface potentials provide a strong selective pressure, at the species and strain level, for both solid surface respirators and fermentative microbes throughout the EET-active community development.

Physical Chemistry Chemical Physics, 2014

The last decade of research has made significant strides toward practical applications of Microbi... more The last decade of research has made significant strides toward practical applications of Microbial Fuel Cells (MFCs); however, design improvements and operational optimization cannot be realized without equally considering engineering designs and biological interfacial reactions. In this study, the main factors contributing to MFCs' overall performance and their influence on MFC reproducibility are discussed. Two statistical approaches were used to create a map of MFC components and their expanded uncertainties, principal component analysis (PCA) and uncertainty of measurement results (UMR). PCA was used to identify the major factors influencing MFCs and to determine their ascendency over MFC operational characteristics statistically. UMR was applied to evaluate the factors' uncertainties and estimate their level of contribution to the final irreproducibility. In order to simplify the presentation and concentrate on the MFC components, only results from Shewanella spp. were included; however, a similar analysis could be applied for any DMRB or microbial community. The performed PCA/UMR analyses suggest that better reproducibility of MFC performance can be achieved through improved design parameters. This approach is exactly opposite to the MFC optimization and scale up approach, which should start with improving the bacteria-electrode interactions and applying these findings to well-designed systems.

Journal of Bioscience and Bioengineering, 2013

We report the development of microbial populations and changes in their electrochemical productio... more We report the development of microbial populations and changes in their electrochemical production during a 2-month study of a two-chamber microbial fuel cell (MFC). The original inoculum was taken from anaerobic enrichment cultures with soil as the inoculum, and lactate as the exogenous electron donor. Power density (PD), coulombic production (CP), and coulombic efficiency (CE) increased rapidly, reaching high values (320 mW m L3 , 65 Q, and 12.5%, respectively) in 12e16 days. Under these conditions, several major microbial taxa dominated the anode population. The medium solution in the cathode chamber decreased with aeration, resulting in a decrease in PD to 55 mW m L3 at day 20. Refilling the cathode chamber around day 30 resulted in restoration of the PD, CP and CE to values equal to or greater than those previously observed. However, after the change in conditions, a marked change in community structure was observed, and high levels of acetate were seen in the anode chamber of the fuel cell for the first time. At day 35, a series of lactate concentrations were used, beginning with low levels and increasing to the 20 mM level originally used (day 46), the PD decreased but was stable at 150 mW m L3 and the acetate concentration in the anode stabilized at about 35 mM. Under these conditions, new major population structures, which were closely related to Propionibacterium, Clostridium, and uncultured bacteria, were observed in the anode. These results suggested that the flexibility of community structure was important for sustainable electricity production.

Biosensors and Bioelectronics, 2008

Applied and Environmental Microbiology, 2007

Journal of Power Sources, 2010

Membrane electrode assemblies were prepared following procedures adopted in the fabrication of po... more Membrane electrode assemblies were prepared following procedures adopted in the fabrication of polymer electrolyte membrane (PEM) fuel fells and used in microbial fuel cells (MFCs) with Shewanella oneidensis MR-1 as a single culture and sodium lactate as the electron donor. Improved inoculation procedures were developed and fuel cell performance with the biofilm density of microbes over the anode is discussed. A novel procedure to condition the membrane is also presented. Polarization measurements were carried out and power density plots were generated. Power density values of 300 mW m −2 are typically obtained while a maximum value of 600 mW m −2 is demonstrated indicating good performance for a single cell culture.

Enzyme and Microbial Technology, 2011

Environmental Science & Technology, 2010

Microbial fuel cell (MFC) technology has enabled new insights into the mechanisms of electron tra... more Microbial fuel cell (MFC) technology has enabled new insights into the mechanisms of electron transfer from dissimilatory metal reducing bacteria to a solid phase electron acceptor. Using solid electrodes as electron acceptors enables quantitative real-time measurements of electron transfer rates to these surfaces. We describe here an optically accessible, dual anode, continuous flow MFC that enables realtime microscopic imaging of anode populations as they develop from single attached cells to a mature biofilms. We used this system to characterize how differences in external resistance affect cellular electron transfer rates on a per cell basis and overall biofilm development in Shewanella oneidensis strain MR-1. When a low external resistance (100 Ω) was used, estimates of current per cell reached a maximum of 204 fA/cell (1.3 × 10 6 ecell -1 sec -1 ), while when a higher (1 MΩ) resistance was used, only 75 fA/cell (0.4 × 10 6 ecell -1 sec -1 ) was produced. The 1 MΩ anode biomass consistently developed into a mature thick biofilm with tower morphology (>50 µm thick), whereas only a thin biofilm (<5 µm thick) was observed on the 100 Ω anode. These data suggest a link between the ability of a surface to accept electrons and biofilm structure development.