Orianna Bretschger

The functional and taxonomic microbial dynamics of duplicate electricity-consuming methanogenic communities were observed over a 6 months period to characterize the reproducibility, stability and recovery of electromethanogenic consortia. The highest rate of methanogenesis was 0.72 mg-CH4/L/day, which occurred during the third month of enrichment when multiple methanogenic phylotypes and associated Desulfovibrionaceae phylotypes were present in the electrode-associated microbial community… Show more

The functional and taxonomic microbial dynamics of duplicate electricity-consuming methanogenic communities were observed over a 6 months period to characterize the reproducibility, stability and recovery of electromethanogenic consortia. The highest rate of methanogenesis was 0.72 mg-CH4/L/day, which occurred during the third month of enrichment when multiple methanogenic phylotypes and associated Desulfovibrionaceae phylotypes were present in the electrode-associated microbial community. Results also suggest that electromethanogenic microbial communities are very sensitive to electron donor-limiting open-circuit conditions. A 45 min exposure to open-circuit conditions induced an 87% drop in volumetric methane production rates. Methanogenic performance recovered after 4 months to a maximum value of 0.30 mg-CH4/L/day under set potential operation (-700 mV vs Ag/AgCl); however, current consumption and biomass production was variable over time. Long-term functional and taxonomic analyses from experimental replicates provide new knowledge toward understanding how to enrich electromethanogenic communities and operate bioelectrochemical systems for stable and reproducible performance. Show less

Microorganisms almost always exist as mixed communities in nature. While the significance of
microbial community activities is well appreciated, a thorough understanding about how microbial
communities respond to environmental perturbations has not yet been achieved. Here we have
used a combination of metagenomic, genome binning, and stimulus-induced metatranscriptomic
approaches to estimate the metabolic network and stimuli-induced metabolic switches existing in
a complex… Show more

Microorganisms almost always exist as mixed communities in nature. While the significance of
microbial community activities is well appreciated, a thorough understanding about how microbial
communities respond to environmental perturbations has not yet been achieved. Here we have
used a combination of metagenomic, genome binning, and stimulus-induced metatranscriptomic
approaches to estimate the metabolic network and stimuli-induced metabolic switches existing in
a complex microbial biofilm that was producing electrical current via extracellular electron transfer
(EET) to a solid electrode surface. Two stimuli were employed: to increase EET and to stop EET. An analysis of cell activity marker genes after stimuli exposure revealed that only two strains within
eleven binned genomes had strong transcriptional responses to increased EET rates, with one
responding positively and the other responding negatively. Potential metabolic switches between
eleven dominant members were mainly observed for acetate, hydrogen, and ethanol metabolisms.
These results have enabled the estimation of a multi-species metabolic network and the associated
short-term responses to EET stimuli that induce changes to metabolic flow and cooperative or
competitive microbial interactions. This systematic meta-omics approach represents a next step
towards understanding complex microbial roles within a community and how community members
respond to specific environmental stimuli. Show less

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’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… Show 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’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. Show less

Microbial fuel cells (MFCs) are devices that exploit microorganisms as “biocatalysts” to
recover energy from organic matter in the form of electricity. MFCs have been explored as
possible energy neutral wastewater treatment systems; however, fundamental knowledge
is still required about how MFC-associated microbial communities are affected by different
operational conditions and can be optimized for accelerated wastewater treatment rates.
In this study, we explored how… Show more

Microbial fuel cells (MFCs) are devices that exploit microorganisms as “biocatalysts” to
recover energy from organic matter in the form of electricity. MFCs have been explored as
possible energy neutral wastewater treatment systems; however, fundamental knowledge
is still required about how MFC-associated microbial communities are affected by different
operational conditions and can be optimized for accelerated wastewater treatment rates.
In this study, we explored how electricity-generating microbial biofilms were established at
MFC anodes and responded to three different operational conditions during wastewater
treatment: 1) MFC operation using a 750 U external resistor (0.3 mA current production); 2)
set-potential (SP) operation with the anode electrode potentiostatically controlled to
þ100 mV vs SHE (4.0 mA current production); and 3) open circuit (OC) operation (zero
current generation). For all reactors, primary clarifier effluent collected from a municipal
wastewater plant was used as the sole carbon and microbial source. Batch operation
demonstrated nearly complete organic matter consumption after a residence time of 8e12
days for the MFC condition, 4e6 days for the SP condition, and 15e20 days for the OC
condition. These results indicate that higher current generation accelerates organic matter
degradation during MFC wastewater treatment. The microbial community analysis was
conducted for the three reactors using 16S rRNA gene sequencing. Although the inoculated
wastewater was dominated by members of Epsilonproteobacteria, Gammaproteobacteria, and
Bacteroidetes species, the electricity-generating biofilms in MFC and SP reactors were
dominated by Deltaproteobacteria and Bacteroidetes. Within Deltaproteobacteria, phylotypes
classified to family Desulfobulbaceae and Geobacteraceae increased significantly under the SP
condition with higher current generation; however those phylotypes were not found in the
OC reactor. Show less

Microbial respiration via extracellular electron transfer (EET) is a ubiquitous reaction that
occurs throughout anoxic environments and is a driving force behind global biogeochemical
cycling of metals. Here we identify specific EET-active microbes and genes in a diverse biofilm
using an innovative approach to analyse the dynamic community-wide response to changing
EET rates. We find that the most significant gene expression responses to applied EET stimuli
occur in only two… Show more

Microbial respiration via extracellular electron transfer (EET) is a ubiquitous reaction that
occurs throughout anoxic environments and is a driving force behind global biogeochemical
cycling of metals. Here we identify specific EET-active microbes and genes in a diverse biofilm
using an innovative approach to analyse the dynamic community-wide response to changing
EET rates. We find that the most significant gene expression responses to applied EET stimuli
occur in only two microbial groups, Desulfobulbaceae and Desulfuromonadales. Metagenomic
analyses reveal high coverage draft genomes of these abundant and active microbes. Our
metatranscriptomic results show known and unknown genes that are highly responsive to EET
stimuli and associated with our identified draft genomes. This new approach yields a comprehensive
image of functional microbes and genes related to EET activity in a diverse community, representing the next step towards unravelling complex microbial roles within a community and how microbes adapt to specific environmental stimuli. Show less

Microbial fuel cell (MFC) systems employ the catalytic activity of microbes to produce electricity from the oxidation of organic, and in some cases inorganic, substrates. MFC systems have been primarily explored for their use in bioremediation and bioenergy applications; however, these systems also offer a unique strategy for the cultivation of synergistic microbial communities. It has been hypothesized that the mechanism(s) of microbial electron transfer that enable electricity production in… Show more

Microbial fuel cell (MFC) systems employ the catalytic activity of microbes to produce electricity from the oxidation of organic, and in some cases inorganic, substrates. MFC systems have been primarily explored for their use in bioremediation and bioenergy applications; however, these systems also offer a unique strategy for the cultivation of synergistic microbial communities. It has been hypothesized that the mechanism(s) of microbial electron transfer that enable electricity production in MFCs may be a cooperative strategy within mixed microbial consortia that is associated with, or is an alternative to, interspecies hydrogen (H2) transfer. Microbial fermentation processes and methanogenesis in ruminant animals are highly dependent on the consumption and production of H2in the rumen. Given the crucial role that H2 plays in ruminant digestion, it is desirable to understand the microbial relationships that control H2 partial pressures within the rumen; MFCs may serve as unique tools for studying this complex ecological system. Further, MFC systems offer a novel approach to studying biofilms that form under different redox conditions and may be applied to achieve a greater understanding of how microbial biofilms impact animal health. Here, we present a brief summary of the efforts made towards understanding rumen microbial ecology, microbial biofilms related to animal health, and how MFCs may be further applied in ruminant research. Show less

To date several different strains of Shewanella have been sequenced; however, many of these isolates have not been evaluated in microbial fuel cell (MFC) systems. Here we present a summary of power densities, current densities, cell attachment, and coulombic efficiencies for eight different Shewanella strains in two different MFC configurations. Our results show that different Shewanella strains have unique characteristics as MFC biocatalysts and that strain S. putrefaciens W3-18-1… Show more

To date several different strains of Shewanella have been sequenced; however, many of these isolates have not been evaluated in microbial fuel cell (MFC) systems. Here we present a summary of power densities, current densities, cell attachment, and coulombic efficiencies for eight different Shewanella strains in two different MFC configurations. Our results show that different Shewanella strains have unique characteristics as MFC biocatalysts and that strain S. putrefaciens W3-18-1 significantly outperforms S. oneidensis MR-1. Further, these results suggest that Shewanella strain performance in MFCs is strongly impacted by system parameters such as buffer composition and ion exchange membrane selection. Show less

Shewanella oneidensis MR-1 is a gram-negative facultative anaerobe capable of utilizing a broad range of electron acceptors, including several solid substrates. S. oneidensis MR-1 can reduce Mn(IV) and Fe(III) oxides and can produce current in microbial fuel cells. The mechanisms that are employed by S. oneidensis MR-1 to execute these processes have not yet been fully elucidated. Several different S. oneidensis MR-1 deletion mutants were generated and tested for current production and metal… Show more

Shewanella oneidensis MR-1 is a gram-negative facultative anaerobe capable of utilizing a broad range of electron acceptors, including several solid substrates. S. oneidensis MR-1 can reduce Mn(IV) and Fe(III) oxides and can produce current in microbial fuel cells. The mechanisms that are employed by S. oneidensis MR-1 to execute these processes have not yet been fully elucidated. Several different S. oneidensis MR-1 deletion mutants were generated and tested for current production and metal oxide reduction. The results showed that a few key cytochromes play a role in all of the processes but that their degrees of participation in each process are very different. Overall, these data suggest a very complex picture of electron transfer to solid and soluble substrates by S. oneidensis MR-1. Show less