Aspartate in the intestine: dual service as anaerobic electron acceptor and nitrogen source

Summary Fumarate was previously known to serve as an anaerobic electron acceptor by E . coli when colonizing the mammalian intestine, but the source of that fumarate was elusive. In this issue, Unden and coworkers demonstrate that l ‐aspartic acid is the source of fumarate that drives anaerobic respiration by colonized E . coli (Schubert et al ., 2021). Moreover, Schubert et al ., establish that E . coli is able to grow anaerobically by using aspartate as a sole source of nitrogen. These groundbreaking findings indicate that a single amino acid – aspartate – supports anaerobic respiration and acquisition of nitrogen by E . coli in the intestine.