(718d) High-Throughput Characterization of Extracellular Electron Transfer (EET)

Extracellular electron transfer (EET) is a microbial anaerobic respiration process where the oxidation of carbon sources is coupled to the reduction of extracellular metal species. Microbes capable of performing EET are found across multiple environments including the soil and gut microbiomes. However, the role that these microbes play in these complex environments is still poorly understood. Identifying new organisms capable of EET is often challenging and low-throughput. This extracellular process can make study in a batch culture difficult, as it cannot trace reduction to a given microbe. In bulk enrichments, resource competition often results in the top performers outcompeting in microbial reduction screens. This inherently couples growth to the detection of an EET-capable organism and limits the scope by linking fitness to EET. Previously, we have coupled EET from the model electroactive organism S. oneidensis to a copper-redox catalysis to perform Cu(I)-catalyzed Alkyne-Azide Cycloadditon (CuAAC) and produce a fluorescent small molecule. Leveraging this, we retrofitted a benchtop microfluidic system to perform oxygen-limited CuAAC to screen for EET-activity. A droplet microfluidic system circumvents several drawbacks in traditional detection of EET by isolating individual microbes. This removes microbe-microbe resource competition as well as linking back specific extracellular reactions to an individual cell. We found this allowed us to selectively enrich for EET-capable organisms. When applying this system to examine a sediment sample gathered from Lake Austin, we discovered previously unreported EET-capable bacteria. In summary, we report a companion method for traditional EET screens which allow for the detection of low abundance, and non-growth related EET-capable microbes.