The diversity of terminal electron acceptors across eukaryotes

The flow of electrons is essential for life. To sustain metabolic flux, organisms efficiently transfer electrons to terminal electron acceptors, which range from inorganic nutrients to intracellularly derived organic metabolites. While the rise of atmospheric oxygen favored the expansion of high-yield aerobic respiration, the diversity of anaerobic electron acceptors remains important for organismal and ecological health, particularly in response to fluctuations in nutrient availability. This review summarizes respiratory and fermentative electron acceptors across eukaryotes, focusing on the evolution of anaerobic pathways. We highlight how ancient metabolic strategies have been conserved and modified to support organisms' adaptation to diverse environmental niches and to sustain biological resilience.