Microbiological aspects of microbial electrolysis cells: Isolation, screening, and electron transfer mechanisms

Biohydrogen is a leading candidate in the global shift toward renewable energy, offering a sustainable solution to reduce reliance on fossil fuels. This review underscores the use of microbial electrolysis cells (MECs) as a viable strategy to address increasing energy demands. In MECs, extracellular electron transfer (EET) is a vital mechanism that enables microorganisms to channel electrons (e⁻) from organic donors to external acceptors. Exo-electrogenic bacteria, viz., Geobacter, Shewanella, Pseudomonas, Nitrospira, and Desulfovibrio, are frequently reported for their ability to utilize Iron: Fe (III) and Manganese: Mn (III/IV) as electron acceptors, which can be replaced with electrodes to drive proton reduction and hydrogen (H2) generation. The use of renewable substrates in fermentation processes further strengthens the commercial feasibility of biohydrogen production, while the molecular traits of microbes provide insights into optimizing H2 production. Despite encouraging laboratory-scale demonstrations, challenges persist due to variability in recovery methods and the limited microbial diversity explored. Expanding the repertoire of exo-electrogens and refining MEC configurations are critical to achieving higher yields. Overall, biohydrogen stands out as a clean, eco-friendly energy resource, with microbial electrolysis offering a sustainable energy technology.