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Extracellular electron transfer explainedArpita Bose, PhD from Washington University in St. Louis, guides us through host-associated impacts and biotechnological applications of extracellular electron transfer in electrochemically active bacteria. Electron flow and oxidative and reductive reactions, referred to as “redox reactions,” collectively impact the outcomes of biochemical pathways essential for cell growth, energy conservation, and stress response throughout various organisms. An example of these organisms is electrochemically active bacteria (EAB), which can link internal redox reactions with external electron acceptors or donors via a process known as extracellular electron transfer (EET).
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This content will become publicly available on January 31, 2026
Single-cell phenotyping of extracellular electron transfer via microdroplet encapsulation
ABSTRACT Electroactive organisms contribute to metal cycling, pollutant removal, and other redox-driven environmental processes via extracellular electron transfer (EET). Unfortunately, developing genotype-phenotype relationships for electroactive organisms is challenging because EET is necessarily removed from the cell of origin. Microdroplet emulsions, which encapsulate individual cells in aqueous droplets, have been used to study a variety of extracellular phenotypes but have not been applied to investigate EET. Here, we describe the development of a microdroplet emulsion system to sort and enrich EET-capable organisms from complex populations. We validated our system using the model electrogenShewanella oneidensisand described the tooling of a benchtop microfluidic system for oxygen-limited conditions. We demonstrated the enrichment of strains exhibiting electroactive phenotypes from mixed wild-type and EET-deficient populations. As a proof-of-concept application, we collected samples from iron sedimentation in Town Lake (Austin, TX) and subjected them to microdroplet enrichment. We measured an increase in electroactive organisms in the sorted population that was distinct compared to a population growing in bulk culture with Fe(III) as the sole electron acceptor. Finally, two bacterial species not previously shown to be EET-capable,Cronobacter sakazakiiandVagococcus fessus, were further cultured and characterized for electroactivity. Our results demonstrate the utility of microdroplet emulsions for isolating and identifying EET-capable bacteria.IMPORTANCEThis work outlines a new high-throughput method for identifying electroactive bacteria from mixed populations. Electroactive bacteria play key roles in iron trafficking, soil remediation, and pollutant degradation. Many existing methods for identifying electroactive bacteria are coupled to microbial growth and fitness—as a result, the contributions from weak or poor-growing electrogens are often muted. However, extracellular electron transfer (EET) has historically been difficult to study in high-throughput in a mixed population since extracellular reduction is challenging to trace back to the parent cell and there are no suitable fluorescent readouts for EET. Our method circumvents these challenges by utilizing an aqueous microdroplet emulsion wherein a single cell is statistically isolated in a pico- to nano-liter-sized droplet. Then, via fluorescence obtained from copper reduction, the mixed population can be fluorescently sorted and gated by performance. Utilizing our technique, we characterize two previously unrecognized weak electrogensVagococcus fessusandCronobacter sakazakii.
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- Award ID(s):
- 1944334
- PAR ID:
- 10618301
- Editor(s):
- Nikel, Pablo Ivan
- Publisher / Repository:
- American Society for Microbiology
- Date Published:
- Journal Name:
- Applied and Environmental Microbiology
- Volume:
- 91
- Issue:
- 1
- ISSN:
- 0099-2240
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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